Maximal Vasodilation Research Articles

No impact of biological sex on nitric oxide contribution to cutaneous vascular response to 39ºC local heating

Purpose: The contribution of endothelial nitric oxide (NO) to vasodilation (%NO contribution) is a significant indicator of risk of cardiovascular disease development. Local skin heating to either 42 ºC or 39 ºC is used to determine mechanisms of vasodilation in health and disease, specifically to investigate %NO contribution. Women have lower %NO contribution in the cutaneous vasculature than men in the early follicular phase of the menstrual cycle, when the circulating vasoactive reproductive hormones are at their lowest concentration. However, this phase represents only a brief portion of the menstrual cycle. We aimed to determine the overall impact of biological sex on %NO contribution to cutaneous vasodilation utilizing a 39ºC local heating protocol, which better isolates the endothelial NO-synthase pathway. We tested women randomly during any phase of the menstrual cycle. We hypothesized that women would demonstrate greater NO-dependent cutaneous vasodilation than men in response to 39ºC local heating. Methods: Data are represented as mean(SD). An intradermal microdialysis fiber was placed in the ventral forearms of 12 men and 13 women [24.2(4.6) years]. Local heaters and laser-Doppler flowmetry probes were used to measure red blood cell flux (perfusion units, PU). Cutaneous vascular conductance (CVC) was calculated as laser-Doppler PU/mean arterial pressure. A standard 39ºC local heating protocol was conducted wherein PU was continuously collected at rest (10 minutes), then the local temperature was increased to 39ºC. After PU reached a steady plateau (~40 minutes), the NO synthase inhibitor 15 mM NG-nitro-L-arginine methyl ester (L-NAME) was perfused. Maximal vasodilation was induced by heating to 43ºC and perfusing 28 mM sodium nitroprusside and normalized to %CVCmax. %NO contribution was calculated as the absolute percentage difference between %CVCmax of 39ºC plateau and %CVCmax of L-NAME steady-state. We compared both CVC and %CVCmax between groups with two-way ANOVA and the %NO contribution with unpaired t-tests. Results: The %NO contribution was not different between sexes [men 48(23)%, women 39(17)%; P = 0.26]. There was no effect of sex on either absolute CVC [men 0.717(0.29) PU, women 0.73(0.48) PU at 39ºC phase] or %CVCmax [men 69(31)%, women 54(20)% at 39ºC phase] at any stage of the 39ºC local heating protocol (main effects P ≥ 0.08). Conclusion: These data indicate there is no impact of biological sex on the vasodilatory response of the cutaneous vasculature to 39ºC local heating in young healthy adults when women are tested at random across the menstrual cycle. Funding: National Institutes of Health Grant T-32-5T32AG049676 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

High antioxidant load impairs cutaneous microvascular function in healthy women

PURPOSE: Human cutaneous circulation is used as an in vivo bioassay to examine mechanisms of systemic vascular dysfunction in cohorts of patients with accelerated cardiovascular disease risk. Local drug infusions, including atorvastatin (statin; LOX inhibitor) and systemic interventions to investigate anti-inflammatory mechanisms (e.g., oral salsalate) have been used to elucidate mechanisms underlying microvascular dysfunction. However, in healthy cohorts, high antioxidant load can attenuate total vasodilation and nitric oxide (NO)-dependent vasodilation. Thus, we aimed to examine endothelial function during high antioxidant load from these localized and systemic treatments in healthy control groups. We hypothesized that combined localized and systemic treatments will attenuate endothelial function in healthy women. METHODS: In a randomized placebo control design, oral salsalate (1500mg/twice daily/5 days) was used to assess the impact of systemic inflammation on cutaneous vascular function. Four intradermal microdialysis fibers were placed into the intradermal space of the ventral forearm of six healthy women (32±7 years). Laser-Doppler flowmeter probes, used to measure cutaneous blood flow, were placed in local heating units set to 33°C. Increasing concentrations of acetylcholine (ACh; endothelium-dependent vasodilator) from 10 -10 to 10 -1 M were co-perfused with one of the following: Lactated Ringer’s (control), 0.02 mM statin, 15 mM N G -nitro-L-arginine methyl ester (L-NAME; nitric oxide synthase inhibitor), and statin + L-NAME (COMBO) sequentially for 5 min each. Following the dose-response protocol, maximal cutaneous vasodilation was induced by increasing local skin temperature to 43°C and perfusing 28 mM sodium nitroprusside. Cutaneous vascular conductance (CVC) was calculated as the quotient of red blood cell flux and mean arterial pressure and normalized as a percentage of the site-specific maximum (%CVC max ). Data at each intervention were compared with control using a two-way (dose x site) analysis of variance. Responses at each dosage were compared using paired t-tests and corrected for multiple comparisons. RESULTS: Following oral salsalate, there was no difference in the %CVC max response to ACh with local L-NAME (p=0.896) or COMBO interventions (p=0.617) as compared to the placebo. However, following oral salsalate, there was a significant reduction in %CVC max in the statin treated site at higher ACh concentrations (10 -5 M, 10 -4 M, 10 -3 M; all p<0.01). CONCLUSION: Endothelial function was attenuated when subjects were introduced to a combination of oral salsalate and statin localized treatments. Five-day oral salsalate intake and local statin may result in high antioxidant load in healthy women creating a shift in redox balance, thus leading to impaired endothelial function. Supported by NIH Grant R01 HL161000 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The effects of standard and soy-free chow on cerebral artery function in ovariectomized female mice

As females age, they transition through menopause, experiencing a decrease in estrogen and an increase in cardiovascular and neurodegenerative disease risk. When studying the effects of menopause in mice, modeled by ovariectomy, it is important to consider the effects of diet. Most standard rodent chows contain phytoestrogen-rich soybean meal, which can mimic the effects of estrogen. Understanding the impact of this soybean meal on outcomes is crucial to proper experimental design. Thus, the aim of this study was to compare the effects of standard and soy-free chows on cerebral artery endothelial function and cognitive function. We studied young female C57Bl/6J mice (n=43; ~6 months) divided into three groups: sham-controls on a soy-free diet (sham-SF), ovariectomized on a soy-free diet (OVX-SF), or OVX on a standard chow diet (OVX-SC). We assessed endothelium-dependent and -independent vasodilation in isolated pressurized posterior cerebral arteries (PCAs). We measured gene expression in cerebral arteries by real-time PCR. To assess behavioral function, we measured instinctual behavior via nest building. Data are presented as mean±SD. Compared with sham-SF, OVX-SF mice had impaired PCA endothelium-dependent vasodilation as evidenced by a maximal response that was 21% lower to acetylcholine (ACh, 60±14% vs. 47±14%, p=0.002) and 27% lower to insulin (52±17% vs. 38±8%, p=0.005). OVX-SC mice had a 27% greater PCA maximal vasodilation to insulin compared with OVX-SF mice (52±11% vs. 38±8%, p=0.001). The PCA responses to ACh and insulin did not differ between sham-SF and OVX-SC (p>0.05). Additionally, the PCA response to ACh and insulin in the presence of nitric oxide synthase inhibitor L-NAME did not differ between groups (p>0.05). Endothelium-independent vasodilation, measured as the PCA response to sodium nitroprusside, also did not differ between groups (p>0.05). There was a trend for lower gene expression of superoxide dismutase 2 ( Sod2) in cerebral arteries from OVX-SF mice (0.7±0.2 AU) compared with OVX-SC (1.0±0.4 AU, p=0.14) but this difference did not reach statistical significance. Cerebral artery gene expression was not different between groups for Esr1 (estrogen receptor α), Insr (insulin receptor), Slca2 (GLUT1), Sod1, or Sod3 (all p>0.05). Lastly, nest building scores were higher in the OVX-SC (4.3±0.5 AU) compared with sham-SF (3.2±1.2 AU, p=0.02) and OVX-SF (3.2±1.0 AU, p=0.04) mice. In summary, we found that ovariectomy impairs endothelial function in cerebral arteries by reducing nitric oxide bioavailability, but a diet containing soy mitigates these effects of ovariectomy. In addition, a diet containing soy leads to better instinctual nest-building behavior in mice. These findings highlight the importance of considering dietary soy when performing vascular and behavior tests in mice, particularly when interested in the effects of sex hormones. Luvaas Family Fund This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Application of Multiscale Sample Entropy in Assessing Effects of Exercise Training on Skin Blood Flow Oscillations in People with Spinal Cord Injury

Spinal cord injury (SCI) causes a disruption of autonomic nervous regulation to the cardiovascular system, leading to various cardiovascular and microvascular diseases. Exercise training is an effective intervention for reducing risk for microvascular diseases in healthy people. However, the effectiveness of exercise training on improving microvascular function in people with SCI is largely unknown. The purpose of this study was to compare blood flow oscillations in people with spinal cord injury and different physical activity levels to determine if such a lifestyle might influence skin blood flow. A total of 37 participants were recruited for this study, including 12 athletes with SCI (ASCI), 9 participants with SCI and a sedentary lifestyle (SSCI), and 16 healthy able-bodied controls (AB). Sacral skin blood flow (SBF) in response to local heating at 42 °C for 50 min was measured using laser Doppler flowmetry. The degree of the regularity of blood flow oscillations (BFOs) was quantified using a multiscale entropy approach. The results showed that BFO was significantly more irregular in ASCI and AB compared to SSCI during the maximal vasodilation period. Our results also demonstrate that the difference in the regularity of BFOs between original SBF signal and phase-randomized surrogate time series was larger in ASCI and AB compared to SSCI. Our findings indicate that SCI causes a loss of complexity of BFOs and exercise training may improve complexity in people with SCI. This study demonstrates that multiscale entropy is a sensitive method for detecting differences between different categories of people with SCI and might be able to detect effects of exercise training related to skin blood flow.

Pharmacological modulation of adrenergic tone alters the vasodilatory response to passive leg movement in young but not in old adults.

The age-related increase in α-adrenergic tone may contribute to decreased leg vascular conductance (LVC) both at rest and during exercise in the old. However, the effect on passive leg movement (PLM)-induced LVC, a measure of vascular function, which is markedly attenuated in this population, is unknown. Thus, in eight young (25 ± 5 yr) and seven old (65 ± 7 yr) subjects, this investigation examined the impact of systemic β-adrenergic blockade (propanalol, PROP) alone, and PROP combined with either α1-adrenergic stimulation (phenylephrine, PE) or α-adrenergic inhibition (phentolamine, PHEN), on PLM-induced vasodilation. LVC, calculated from femoral artery blood flow and pressure, was determined and PLM-induced Δ peak (LVCΔpeak) and total vasodilation (LVCAUC, area under curve) were documented. PROP decreased LVCΔpeak (PROP: 4.8 ± 1.8, Saline: 7.7 ± 2.7 mL·mmHg-1, P < 0.001) and LVCAUC (PROP: 1.1 ± 0.7, Saline: 2.4 ± 1.6 mL·mmHg-1, P = 0.002) in the young, but not in the old (LVCΔpeak, P = 0.931; LVCAUC, P = 0.999). PE reduced baseline LVC (PE: 1.6 ± 0.4, PROP: 2.3 ± 0.4 mL·min-1·mmHg-1, P < 0.01), LVCΔpeak (PE: 3.2 ± 1.3, PROP: 4.8 ± 1.8 mL·min-1·mmHg-1, P = 0.004), and LVCAUC (PE: 0.5 ± 0.4, PROP: 1.1 ± 0.7 mL·mmHg-1, P = 0.011) in the young, but not in the old (baseline LVC, P = 0.199; LVCΔpeak, P = 0.904; LVCAUC, P = 0.823). PHEN increased LVC at rest and throughout PLM in both groups (drug effect: P < 0.05), however LVCΔpeak was only improved in the young (PHEN: 6.4 ± 3.1, PROP: 4.4 ± 1.5 mL·min-1·mmHg-1, P = 0.004), and not in the old (P = 0.904). Furthermore, the magnitude of α-adrenergic modulation (PHEN - PE) of LVCΔpeak was greater in the young compared with the old (Young: 3.35 ± 2.32, Old: 0.40 ± 1.59 mL·min-1·mmHg-1, P = 0.019). Therefore, elevated α-adrenergic tone does not appear to contribute to the attenuated vascular function with age identified by PLM.NEW & NOTEWORTHY Stimulation of α1-adrenergic receptors eliminated age-related differences in passive leg movement (PLM) by decreasing PLM-induced vasodilation in the young. Systemic β-blockade attenuated the central hemodynamic component of the PLM response in young individuals. Inhibition of α-adrenergic receptors did not improve the PLM response in older individuals, though withdrawal of α-adrenergic modulation augmented baseline and maximal vasodilation in both groups. Accordingly, α-adrenergic signaling plays a role in modulating the PLM vasodilatory response in young but not in old adults, and elevated α-adrenergic tone does not appear to contribute to the attenuated vascular function with age identified by PLM.

Influence of nitro ruthenium isomerization on photochemically induced nitric oxide release: Vasorelaxant activities

We have synthesized cis-[Ru(bpy)2(NO2-κN)Ln-](n-1) and cis-[Ru(bpy)2(NO2-κO)L n-](n-1) (bpy = 2,2′-bipyridine; k = indication of the coordinated center to Ruthenium; L = pyridine type ligand) by reacting cis-[Ru(bpy)2(H2O)Ln-](n-2) with sodium nitrite or conducting basic cis-[Ru(bpy)2NO(Ln-)](n-3) hydrolysis. Photolysis at the metal-ligand charge transfer band (MLCT) of the isomers yielded nitric oxide (NO) as determined by NO measurement. The NO photorelease rates obtained upon 447 nm laser irradiation of the ruthenium complexes showed that cis-[Ru(bpy)2(NO2-κO)Ln-](n-1) released NO three times faster than cis-[Ru(bpy)2(NO2-κN)Ln-](n-1). We investigated endothelium-dependent vasodilation induced by cis-[Ru(bpy)2(4-pic)(NO2-κN)]+ and cis-[Ru(bpy)2(4-pic)(NO2-κO)]+ (4-pic = 4-picoline) in isolated 3 mm aortic rings precontracted with L-phenylephrine. Maximum vasodilation was achieved under 447 nm laser irradiation of 0.5 μMol.L−1 ruthenium complexes for 100 s.

Absent Right Coronary Artery in an Active Young Female

Absent Right Coronary Artery in an Active Young Female

Reliability of laser-Doppler flowmetry derived measurements of forearm and calf cutaneous vasodilation during gradual local heating in young adults.

Evaluate reliability of laser-Doppler flowmetry derived cutaneous vasodilation on the upper and lower limbs during gradual local heating. In twenty-eight young adults (21 (SD 3) years, 14 females), absolute cutaneous vascular conductance (CVCabs) and CVC normalized to maximum vasodilation at 44 °C (%CVCmax) were assessed at two adjacent sites on each of the forearm and calf during gradual local skin heating (33-42 °C at 1 °C·5 min-1) for two identical trials (~1 week apart). Responses were assessed for baseline, the steady-state heating plateau at 42 °C and the span (i.e. plateau-baseline). Between-day reliability was characterized as measurement consistency across trials. Within-day reliability was characterized as within-limb measurement consistency across adjacent skin sites. Between- and within-day absolute reliability (coefficient of variation) generally improved with heating, from poor (>25 %) at baseline to good (<10 %) for %CVCmax and moderate (10-25 %) for CVCabs for plateau and span. However, relative reliability (intraclass correlation coefficient) was generally not acceptable (≤0.70) for any condition. Responses were generally consistent for females and males and there were no major forearm and calf differences. Consistency of CVC estimates improved during gradual local heating with negligible limb and sex differences, which are important considerations for experimental design and interpretation.

Malperfusion in dilated cardiomyopathy: One more link in the pathologic chain?

Dilated cardiomyopathy (DCM) is considered the primary non-ischemic heart disease, but there are controversial data regarding the microcirculatory disturbance in these patients. While the major epicardial vessels are always intact in these patients, the malperfusion of the myocardium of the left ventricle (LV) may be present, and the role of this malperfusion in the progression of the disease is not clear. The non-invasive echocardiographic assessment of the coronary blood flow reveals that it may be increased at rest and decreased during pharmacological stress, leading to a decreased coronary flow reserve.1 Beyond echocardiographic studies, microvascular dysfunction in DCM has been previously investigated with various imaging modalities. Bietenbeck M. et al. performed the quantitative myocardial first-pass perfusion cardiovascular magnetic resonance (CMR) imaging and coronary sinus flow measurements at rest and during maximal vasodilatation which is a well-validated approach for the quantification of global myocardial blood flow in CMR. The blood flow parameters were reduced at rest and during stress in both groups of patients with DCM and hypertrophic cardiomyopathy.2 Interestingly, in another study, it was shown that myocardial blood flow assessed by the CMR in DCM could be elevated at rest with a substantial decrease during the stress-test with adenosine. This corresponds well with the previous echocardiographic findings and also can reflect the possible stress-induced stunning instead of chronic hypoperfusion in DCM.3 Another promising in microcirculation evaluation, though not a fully available modality, is PET. In a study by Yamaguchi et al., the authors observed the regional 18-fluorodesoxiglucose uptake in all patients with ischemic cardiomyopathy in the fasting state, while patients with DCM showed variable patterns of uptake. Nevertheless, when going to glucose loading state, the DCM patients demonstrated mostly non-reversing patterns of uptake, which allows PET to distinguish DCM from ischemic cardiomyopathy.4 (99 m)Tc-methoxy-isobutyl-isonitrile and (123)I-15-(p-iodophenyl)-3(R,S)-methylpentadecanoic acid dual single photon emission computed tomography also provides valuable data on perfusion-metabolism mismatches, which carry the prognostic role in DCM.5 Myocardial contrast echocardiography (MCE) being a more simple, bedside method has been previously found to be helpful in differentiating the DCM and ischemic heart disease in patients with acute onset of heart failure.6 However, another group of authors has the confronting results: the contrast replenishment rate was similar in patients with coronary artery disease and without it.7 In this issue of the Journal of Clinical Ultrasound Sha Tang et al, for the first time the MCE was combined with speckle tracking strain analysis in a layer-specific manner in patients with DCM and compared with the same parameters in healthy volunteers.8 While the poor global and regional LV systolic function assessed by speckle tracking strain in DCM patients in comparison to healthy subjects is awaited, the authors performed the comprehensive analysis of the interaction between segmental parameters by dividing the myocardium into standard segments plus three layers in each segment. Therefore, the data on gradients in strain and perfusion parameters becomes the mainstay of this study. The idea of layer-specific strain analysis is not new, but still can be regarded as a pure experimental method with no clinical implication. For example, in the work by Nagata Y et al. the authors offer Endo/Epi strain ratio for gradient assessment.9 Therefore, the authors demonstrated an interesting correlation between MCE perfusion and longitudinal function at rest in DCM patients with the diffuse pattern of impairment in all segments and layers. Considering the aforementioned CMR-based and PET-based studies, which showed a substantial decrease in coronary flow reserve between rest and stress, the MCE with pharmacological stress could be the rational development of basic ideas, presented in this study. Moreover, the dynamic nature of MCE can give the opportunity for dynamic malperfusion assessment in patients with DCM during stress. In addition, new insights into the pathophysiology of DCM may provide the basis for new clinical trials of various agents, intended to restore the damaged microcirculatory link in the chain of global LV deterioration. The authors have nothing to disclosure. Open Access funding enabled and organized by Projekt DEAL. Not applicable.

PS-B01-2: ASSOCIATION BETWEEN IMPAIRED METABOLIC FUNCTION AND VASCULAR DYSFUNCTION IN METABOLIC SYNDROME

Objectives: Metabolic syndrome is a leading cause for vascular dysfunction and cardiovascular diseases. We have previously shown that vascular functional responses in metabolic syndrome exhibit exaggerated vasocontractility and impaired endothelium-dependent relaxation. However, it remains unclear if a correlation between vascular abnormalities and metabolic disturbances exists. Accordingly, we aimed to explore the association between vascular dysfunction and changes in metabolic parameters in a rodent model of metabolic syndrome, the high fat diet (HFD)-streptozotocin (STZ)-induced diabetes mellitus rat (HFD-D). Design and method: Five weeks old male Wistar albino rats (n = 24) were fed with either HFD (45 kcal% fat) or control diet (10 kcal% fat) for 10 weeks. On week 6, 40 mg/kg STZ and saline were injected intraperitoneally into the HFD and control groups, respectively. At the end of the treatment, metabolic data were collected then rats were euthanized for blood and kidney collection and to measure maximal vasoconstrictor and vasodilator responses of the abdominal aortic rings. Recorded measures also included fasting blood glucose (FBG), plasma total cholesterol (TC), plasma triglyceride (TG), plasma high density lipoprotein (HDL), plasma creatinine (Cr), urinary protein: urinary creatinine (UPC) and kidney index (KI). Results: HFD-D rats had higher FBG, TG, Cr, UPC, and KI compared with controls. HDL was lower in HFD-D while TC remained unchanged. Maximal vasoconstriction to norepinephrine (NE Rmax) was greater in the HFD group compared with controls. Maximal endothelium-dependent vasorelaxation to acetylcholine (ACh Rmax) was blunted in the HFD group relative to controls. A positive correlation between NE Rmax and FBG was found, whereas ACh Rmax was negatively correlated with FBG, KI, UPC and TG. Conclusions: Impaired glucose metabolism, lipid profile and renal function are likely key contributors to vascular dysfunction in metabolic syndrome; however, further mechanistic investigations are required to verify these assumptions.

Effects of sensory nerve blockade on cutaneous microvascular responses to ischemia-reperfusion injury.

Examine the effects of sensory nerve blockade on cutaneous post-occlusive reactive hyperemia (PORH) and local thermal hyperemia (LTH) following prolonged upper limb ischemia. In nine males [28years (standard deviation:6)], volar forearm skin blood flux normalized to maximum vasodilation (%SkBFmax) was assessed at control (CTRL) and sensory nerve blockade (EMLA) treated sites during the PORH response following 20-min of complete arm ischemia and during rapid LTH (33-42°C, 1°C·20s-1, held for ~30-min+20-min at 44°C) before and after ischemia-reperfusion (IR) injury. EMLA increased mean [95% confidence-interval] PORH amplitude by 21%SkBFmax ([9,33]; p=0.003), delayed time to peak by 111s ([40,182]; p=0.007) and increased area under the curve by 19,462%SkBFmax·s ([11,346,27,579]; p<0.001) compared to CTRL. For LTH, EMLA delayed onset time by 76s ([46,106]; p<0.001) Pre-IR and by 46s ([27,65]; p<0.001) Post-IR compared to CTRL. Post-IR onset time was delayed for CTRL by 26s ([8,43]; p=0.007), but was not different for EMLA (p>0.050) compared to Pre-IR. EMLA delayed time to initial peak by 24s ([4,43]; p=0.022, Main time effect) and it attenuated the initial peak by 27%SkBFmax ([12,43]; p=0.002) Pre-IR and by 16%SkBFmax ([3,29]; p=0.020) post-IR compared to CTRL. Post-IR, the initial peak was not different for CTRL (p>0.050), but it was increased by 16%SkBFmax ([5,26]; p=0.005) for EMLA compared to Pre-IR. Neither EMLA nor IR altered the steady-state heating plateau (all p>0.050). For the current model of IR injury, sensory nerves appear to have a negligible influence on the LTH response in non-glabrous forearm skin once vasodilation has been initiated.

Saline-induced coronary hyperemia with continuous intracoronary thermodilution is mediated by intravascular hemolysis

Abstract Objectives To test whether local hemolysis is a potential mechanism of saline-induced coronary hyperemia. Background Absolute coronary flow can be measured by intracoronary continuous thermodilution of saline through the lateral side holes of a dedicated infusion cathete. A saline infusion rate at 15–20 mL/min induces an immediate, steady-state, maximal microvascular vasodilation. The mechanism of this hyperemic response remains unclear. Methods Twelve patients undergoing left and right catheterization were included. The left coronary artery and the coronary sinus were selectively cannulated. Absolute resting and hyperemic coronary flow were measured by continuous intracoronary thermodilution. Arterial and venous samples were collected from the coronary artery and the coronary sinus in five phases: baseline (BL); resting flow measurement (Rest, saline infusion at 10 mL/min); hyperemia (Hyperemia,saline infusion at 20 mL/min); post-hyperemia (Post-Hyperemia, two minutes after the cessation of saline infusion); and control phase (Control, during infusion of saline through the guide catheter at 30 mL/min). Results Hemolysis was visually detected only in the centrifugated venous blood samples collected during the Hyperemia phase. As compared to Rest, during Hyperemia both LDH (131.50±21.89 U/dL [Rest] and 258.33±57.40 U/dL [Hyperemia], p&amp;lt;0.001) and plasma free hemoglobin (PFHb, 4.92±3.82 mg/dL [Rest] and 108.42±46.58 mg/dL [Hyperemia], p&amp;lt;0.001) significantly increased in the coronary sinus. The percentage of hemolysis was significantly higher during the Hyperemia phase (0.04±0.02% [Rest] vs 0.89±0.34% [Hyperemia], p&amp;lt;0.001). Conclusions Saline-induced hyperemia through a dedicated intracoronary infusion catheter is associated with hemolysis. Vasodilatory compounds released locally, like ATP, are likely ultimately responsible for localized microvascular vasodilation. Funding Acknowledgement Type of funding sources: None.

Sustained vasodilation after cold pressor test is an independent predictor of poor survival in primary AL amyloidosis

Abstract Background Primary AL amyloidosis is a rare yet lethal systemic disorder. Dysfunction of the autonomous nervous system due to disease-related nerve infiltration is a common manifestation of AL amyloidosis. Previously published own work indicated that AL patients present sustained paradoxical vasodilation in response to sympathetic stimulus, as assessed by cold pressor test (CPT). The clinical relevance of this finding is unknown. Purpose We sought to investigate the relationship between CPT-induced vascular response and mortality in AL amyloidosis. Methods We consecutively recruited 97 newly diagnosed patients with AL amyloidosis. CPT of the brachial artery was performed before treatment initiation. All measurements were assessed using high resolution ultrasonography (14.0Mhz multifrequency linear array probe, Vivid 7 Pro; General Electric Healthcare, Milwaukee, Wisconsin, USA). The maximum vasodilation of the brachial artery was measured during the sympathetic stimulus and 3 minutes after withdrawal (sustained response). All-cause mortality was defined as the primary end-point of the study. Results Mean age was 66 years with prevalence of male gender. Sustained vasodilation (but not vasodilation during CPT) was associated with heart failure, NYHA stage, BNP and peripheral vascular involvement (p&amp;lt;0.05 for all). Sustained vasodilation after withdrawal of the sympathetic stimulus was significantly associated with mortality as assessed by Cox regression analysis (HR: 1.149, 95% CI 1.042–1.269, p=0.005). This association remained significant after adjustment for age, sex, systolic blood pressure (SBP), nerve involvement and Mayo stage (HR: 1.123, 95% CI 1.014–1.243, p=0.026). A sustained vasodilation ≥3.35% from pre-stimulus diameter was associated with shorter survival (log-rank test, p=0.022, Figure 1). No association between vasodilation during sympathetic stress and mortality was observed. Conclusions In AL amyloidosis, sustained paradoxical vasodilation in response to sympathetic stimulus was associated with poor survival. The clinical utility of this index of vascular autonomic dysfunction as a potential prognostic and therapeutic biomarker in AL amyloidosis merits further investigation. Funding Acknowledgement Type of funding sources: None.

The predominance of endothelium-derived relaxing factors and beta-adrenergic receptor pathways in strong vasorelaxation induced by 4-hydroxybenzaldehyde in the rat aorta.

4-hydroxybenzaldehyde (4HB), known as ρ-hydroxybenzaldehyde, is commonly present in traditional Chinese medicine herb, most frequently used for hypertension treatment. This research aims to determine the potency of 4HB's vasorelaxant action. In the study, the vasodilation effect of 4HB was evaluated using in vitro isolated rat aortic rings assay. The aortic rings were pre-incubated with respective antagonists before being pre-contracted with phenylephrine (PE) and challenged with various concentrations of 4HB for mechanistic action studies. Rmax (maximal vasodilation) and pEC50 (negative logarithm of half-maximal effective concentration) values of each experiment were determined for comparison purposes. 4HB caused vasodilation on endothelium-intact aortic rings which pre-contracted with PE (pEC50 = 3.53±0.05, Rmax = 100.95±4.25%) or potassium chloride (pEC50 = 2.96±0.13, Rmax = 72.13±4.93%). The vasodilation effect of 4HB was significantly decreased in the absence of an endothelium (pEC50 = 2.21±0.25, Rmax = 47.96±4.16%). The atropine, 4-aminopyridine, Nω-nitro-L-arginine methyl ester, glibenclamide, and propranolol significantly reduced the vasorelaxation effect of 4HB. Besides that, 4HB blocked the voltage-operated calcium channel (VOCC) and regulated the intracellular Ca2+ release from the sarcoplasmic reticulum (SR) in the aortic ring. Thus, the results indicated that 4HB exerted its vasodilatory effect via cGMP and β2 pathways, M3-dependent PLC/IP3 pathways, and potassium and calcium channels.

Saline-induced coronary hyperemia with continuous intracoronary thermodilution is mediated by intravascular hemolysis

Background and aimsAbsolute coronary flow can be measured by intracoronary continuous thermodilution of saline through a dedicated infusion catheter (RayFlow®). A saline infusion rate at 15–20 mL/min induces an immediate, steady-state, maximal microvascular vasodilation. The mechanism of this hyperemic response remains unclear. We aimed to test whether local hemolysis is a potential mechanism of saline-induced coronary hyperemia. MethodsTwelve patients undergoing left and right catheterization were included. The left coronary artery and the coronary sinus were selectively cannulated. Absolute resting and hyperemic coronary flow were measured by continuous intracoronary thermodilution. Arterial and venous samples were collected from the coronary artery and the coronary sinus in five phases: baseline (BL); resting flow measurement (Rest, saline infusion at 10 mL/min); hyperemia (Hyperemia, saline infusion at 20 mL/min); post-hyperemia (Post-Hyperemia, 2 min after the cessation of saline infusion); and control phase (Control, during infusion of saline through the guide catheter at 30 mL/min). ResultsHemolysis was visually detected only in the centrifugated venous blood samples collected during the Hyperemia phase. As compared to Rest, during Hyperemia both LDH (131.50 ± 21.89 U/dL [Rest] and 258.33 ± 57.40 U/dL [Hyperemia], p < 0.001) and plasma free hemoglobin (PFHb, 4.92 ± 3.82 mg/dL [Rest] and 108.42 ± 46.58 mg/dL [Hyperemia], p < 0.001) significantly increased in the coronary sinus. The percentage of hemolysis was significantly higher during the Hyperemia phase (0.04 ± 0.02% [Rest] vs 0.89 ± 0.34% [Hyperemia], p < 0.001). ConclusionsSaline-induced hyperemia through a dedicated intracoronary infusion catheter is associated with hemolysis. Vasodilatory compounds released locally, like ATP, are likely ultimately responsible for localized microvascular vasodilation.

Effect of Oral Contraceptive Phase on Mechanisms of Cutaneous Microvascular Function

While the effect of oral contraceptive (OC) use on endothelial function has been previously studied, precise mechanisms of endothelial function in this group of women remains unclear. The purpose of this study was to investigate the contribution of cyclooxygenase (COX), endothelial‐derived hyperpolarizing factors (EDHF), and nitric oxide (NO) to cutaneous microvascular function in women during the low hormone (LH) and high hormone (HH) phases of OC. Five young, healthy women taking monophasic, combined OC of any generation visited the lab twice: once during the LH (d 1‐2 of placebo pills) and once during the HH phase (d 3‐6+ of active pills). Participants were instrumented with three microdialysis fibers, and each site was randomized as control (lactated Ringer's), COX inhibition (10 mM ketorolac), or EDHF inhibition (50 mM tetraethylammonium, TEA). Laser‐Doppler flowmetry and local heaters were used to measure skin blood flow and induce local thermal hyperemia, respectively. Each site was heated from 33°C to 39°C at a rate of 0.1°C/sec. Once a plateau to local heating was established, 20 mM L‐NAME, a NO synthase inhibitor, was infused at each site to quantify NO‐dependent vasodilation. Maximal vasodilation was induced by heating the skin to 43°C and infusing 28 mM sodium nitroprusside. Data are mean ± SD. For baseline, there was a main effect of OC phase (p = 0.03) and treatment (p &lt; 0.001) but no interaction effect (p = 0.21) such that baseline was increased at COX‐inhibited sites (23 ± 3 %CVCmax) compared with control (14 ± 6 %CVCmax; p = 0.03) during the HH phase. For initial peak, there was a main effect of treatment (p &lt; 0.001) but no effect of OC phase (p = 0.99) or interaction effect (p = 0.59) such that initial peak was decreased at EDHF‐inhibited sites during the HH phase (17 ± 6 %CVCmax) compared with control (51 ± 23 %CVCmax; p = 0.02). For local heating plateau, there was a main effect of treatment (p &lt; 0.001) but no effect of OC phase (p = 0.28) or interaction effect (p = 0.21) such that plateau was decreased at EDHF‐inhibited sites during both phases (LH: 18 ± 12 %CVCmax; HH: 20 ± 9 %CVCmax) compared with respective control (LH: 63 ± 13 %CVCmax; HH: 67 ± 23 %CVCmax) and ketorolac sites (LH: 58 ± 21 %CVCmax; HH: 71 ± 12 %CVCmax; all comparisons: p &lt; 0.01). For %NO, there was no observed effect of OC phase (p = 0.77), treatment (p = 0.21), or interaction (p = 0.09). While not statistically significant, there was a large effect size for %NO between LH and HH phases at control sites (LH: 72 ± 15 %NO; HH: 50 ± 23 %NO; Cohen’s d = 1.05). During the LH phase, large effect sizes were observed between control and TEA (48 ± 14 %NO; d = 1.65) sites and control and ketorolac (54 ± 22 %NO; d = 0.96) sites. During the HH phase, a large effect size was observed between control and ketorolac (69 ± 17 %NO; d = 0.94) sites. These preliminary data suggest mechanisms underlying endothelial function vary across OC phase in women. While overall endothelial function (i.e., magnitude of local heating plateau) is similar between OC phases, there may be basal constriction (i.e., increased baseline with COX inhibition) and reduced NO‐dependent dilation during the HH phase. This shift in mechanisms underlying endothelial function in women using OC may contribute to cardiovascular health outcomes.

Monocrotaline‐induced Pulmonary Hypertension Impairs Diaphragm Vasomotor Function

INTRODUCTIONPulmonary hypertension (PH) is a chronic and progressive disease characterized by high arterial blood pressure and compensatory vascular remodeling in the pulmonary circulation. Mounting evidence suggests that the effects of PH extend beyond the pulmonary circulation. In humans and animals, PH induces diaphragm contractile dysfunction and diaphragm muscle atrophy. While the mechanistic bases for the PH‐induced diaphragm dysfunction is relatively unknown, alterations in the vasomotor control of the diaphragm resistance vasculature (i.e. arterioles) may play a key role. Therefore, we tested the hypothesis that PH increases the vasoconstrictor responsiveness and impairs the vasorelaxation of diaphragm arterioles.METHODSAdult female Sprague‐Dawley rats (n=8) were divided into healthy control (HC; n=2), ovariectomized (OVX; n=3), and PH + OVX (n=3). PH + OVX animals were given a single intraperitoneal injection of monocrotaline (MCT; 50mg/kg) to induce PH. Disease progression was then monitored via echocardiography. Once animals developed PH (~3 weeks post injection), the diaphragm was removed and first‐order arterioles (1A) from the medial costal diaphragm were isolated, cannulated, and pressurized at 90 cmH2O. After a 60 min equilibration period and spontaneous tone development, vasoconstrictor responses to potassium chloride (KCl) (10‐100 mM) and endothelium‐dependent and ‐independent vasorelaxation responses to cumulative doses of acetylcholine (ACh) and sodium nitroprusside (SNP) (10‐9 to 10‐4 M) were determined.RESULTSSpontaneous tone (%) development was not different across all three groups (HC: 36 ± 9%; OVX: 33 ± 9%; PH + OVX: 39 ± 2%; P&gt;0.05). Compared to control vessels, maximal percent vasoconstriction with KCl was decreased with OVX (67 ± 2 versus 50 ± 1%; P&lt;0.05). Maximal vasoconstriction (%) was reduced with PH + OVX (36 ± 4%) compared to vessels from both healthy control and OVX groups (P&lt;0.05). Ovariectomy had no effect on endothelium‐dependent vasodilation responses to ACh versus intact control animals (P&gt;0.05). The maximal ACh‐mediated vasodilation with PH + OVX (29 ± 9%) was decreased versus both healthy (45 ± 6%; P&lt;0.05) and OVX animals (41 ± 4%; P&lt;0.05). Across all three groups, there were no differences in percent relaxation with SNP (P&gt;0.05).CONCLUSIONThese findings suggest that estrogen plays a role in the maintenance of K+ channel activity and/or the contribution of K+ channels to diaphragm vasomotor tone, and that PH further disrupts K+ channel function in diaphragm arterioles. In addition, the absence of estrogen in OVX animals had no effect on endothelial function whereas PH + OVX impaired endothelium‐dependent vasorelaxation of diaphragm resistance vessels. These findings suggest that PH, at least in the rodent model utilized herein, elicits endothelial dysfunction in the diaphragm vasculature and provide a potential mechanism for the impaired diaphragm contractile dysfunction in PH patients.

Estradiol Augments Sensory Nerve‐Mediated Vasodilation in Young Women

Local heating of the skin elicits biphasic vasodilation: a sensory nerve‐mediated initial peak (axon reflex) and an endothelial‐dependent plateau. We have previously shown that sex hormones, particularly estradiol (E2), improves cutaneous endothelial‐dependent vasodilation, but less is known about the effects of E2 on cutaneous sensory nerve‐mediated vasodilation.PURPOSEWe tested the hypothesis that E2 enhances sensory‐nerve mediated vasodilation in response to local heating of the skin in young women.METHODSWe retrospectively analyzed data in 15 healthy young women (age 24 ± 4 yr; MAP 84 ± 6 mmHg; BMI 24 ± 3 kg/m2). Endogenous sex hormone production was suppressed with daily administration of a gonadotropin‐releasing hormone antagonist (GnRHant; Ganirelix) for 10 days. E2 (0.1 mg/day, Vivelle‐Dot) was added back via transdermal patch on days 4–10. Cutaneous vasodilatory responses to local heating were measured on days 4 and 10 using laser Doppler flowmetry during microdialysis perfusions of lactated Ringer’s (control), and in a subset of women (n=6), L‐NAME (non‐selective nitric oxide synthase inhibition). Cutaneous vascular conductance (CVC) was calculated during the initial peak of the axon reflex during local heating (42°C) and normalized to maximal vasodilation achieved by perfusion of sodium nitroprusside (28mM) and heating to 43°C.RESULTSSensory nerve‐mediated vasodilation increased during E2 administration compared to GnRHant (E2: 71 ± 15, GnRHant: 57 ± 18 %CVCmax; p=0.046). Blockade of nitric oxide with L‐NAME did not blunt the axon reflex during GnRHant (control: 57 ± 18 vs. L‐NAME: 50 ± 17 %CVCmax; p=0.401) or E2 administration (control: 71 ± 15 vs. L‐NAME: 52 ± 19 %CVCmax; p=0.152).CONCLUSIONThese preliminary findings suggest that E2 enhances sensory nerve‐mediated vasodilation in young women, and that this may occur through mechanisms independent of nitric oxide. Future mechanistic studies isolating the nitric oxide component and other pathways could help elucidate the role of E2 in sensory nerve‐mediated vasodilation.

Effect of Short‐Term Estradiol Exposure on Endothelin‐B Receptor‐Mediated Vasodilation in Postmenopausal Women

Endothelin (ET)‐1 contributes to endothelial dysfunction in postmenopausal women (PMW) via the ETB receptor. We have previously shown that the ETB receptor mediates vasodilation in young women, an effect that is lost in PMW. However, it is unclear if ETB receptor‐mediated dilation can be restored in PMW exposed to E2.PURPOSETo test the hypothesis that E2 exposure restores ETB receptor‐mediated vasodilation in PMW.METHODSWe tested 9 PMW (55±2 yrs, 24±3 kg/m2, 91±5 mmHg) who self‐reported natural menopause and were at least 1 year without menses. We measured vasodilation in the cutaneous microcirculation via local heating using laser Doppler flowmetry coupled with intradermal microdialysis during perfusions of lactated Ringer’s (control), ETB receptor antagonist (BQ‐788, 300nM) and ETA receptor antagonist (BQ‐123, 500nM). Cutaneous vascular conductance (CVC) was calculated during the plateau phase of local heating (42°C), and normalized to maximal vasodilation achieved by perfusion of sodium nitroprusside (28mM) and heating to 43°C. All women were tested at baseline (BL) and after 7 days of E2 (Vivelle‐Dot, 0.1mg/day, transdermal patch) administration (+E2). A two‐way repeated measures ANOVA was performed to compare %CVCmax in PMW before and after E2 exposure. Data presented are mean ± standard deviation.RESULTSE2 administration increased serum estradiol (BL: 45±29 vs +E2: 71±42 pg/mL, P&lt;0.01) and reduced follicle stimulating hormone (BL: 71±13 vs +E2: 57±17 pg/mL, P&lt;0.01), but there were no changes in serum progesterone (BL: 0.57±0.93 vs +E2: 0.53±0.88 pg/mL, P=0.14) nor plasma ET‐1 (BL: 1.62±0.66 vs +E2: 1.54±0.54 pg/mL, P=0.42). E2 administration had no effect on cutaneous microvascular responses (Time P=0.41, Drug P=0.17, Interaction P=0.71). At BL, vasodilatory responses to local heating were not different during control and ETB receptor antagonism (control: 83±8 vs. BQ‐788: 88±6 %CVCmax). Similarly, vasodilation was not altered at BL during ETA receptor antagonism in a subset of women (n=6, control: 83±8 vs. BQ‐123: 87±8 %CVCmax). E2 administration did not improve vasodilation in the control site (BL: 83±8 vs. +E2 85±13 %CVCmax). Furthermore, there was no effect of E2 exposure on cutaneous vasodilatory responses during perfusion of ETB (BL: 88±6 vs. +E2: 89±6 %CVCmax) nor ETA (n=6, BL: 87±8 vs +E2: 92±7 %CVCmax) receptor antagonists.CONCLUSIONThese preliminary data suggest that short‐term E2 exposure does not modulate ETB receptor function in PMW. These findings are in contrast to our observations in young women demonstrating that ETB receptors mediate vasodilation in the presence of E2. The role of alternative therapies to modulate ETB receptor function should be considered in future studies.

Home‐Based Leg Heat Therapy Does Not Improve Vascular Function in Patients with Symptomatic Peripheral Artery Disease

INTRODUCTIONPatients with peripheral artery disease (PAD) suffer from severe exercise intolerance and accelerated rates of functional decline, resulting, in part, from significant endothelial cell dysfunction and the consequent impairment in leg blood flow. Unfortunately, few non‐invasive therapeutic interventions have been shown to ameliorate the microvascular dysfunction in patients with PAD. Repeated exposure to heat therapy (HT) improves endothelial function in sedentary young individuals, but the effects of this therapy on vascular function in patients with PAD remain poorly defined. The objective of the present study was to test the hypothesis that 8 weeks of home‐based leg HT would improve leg vascular function in patients with symptomatic PAD.METHODSThirty‐four patients with symptomatic PAD (66 ± 8 years, ankle‐brachial index: 0.68 ± 0.12) were randomized into one of two groups: home‐based leg HT (HT, n=18) or a control treatment (CON, n=16). Patients in both groups were provided with identical water‐circulating trousers and a portable heating pump and were asked to apply the therapy daily (7 days/week, 90 min per session) for 8 consecutive weeks. The pump issued to participants circulated water through the trousers at 43ºC in the HT group and 33ºC in the control group. Laser‐Doppler flowmetry was used to measure red blood cell flux, an index of skin blood flow, during local skin heating to 39°C for 40 min, followed by 43ºC for 20 min. Cutaneous vascular conductance (CVC) was calculated as red blood cell flux divided by mean arterial pressure and expressed as a percentage of maximal vasodilation (%CVCmax). Calf skeletal muscle perfusion was assessed using arterial spin labeling magnetic resonance imaging (MRI) following circulatory occlusion of the thigh for 5 min.RESULTSFive participants were either withdrawn prior to study completion or failed to complete the 8‐week follow‐up visit. The remaining 29 participants were included in the final analysis (CON: n=14, HT: n=15). Two participants from CON and 4 from HT were unable to undergo the MRI scans. At baseline, local skin heating to 39ºC increased %CVCmax to 55.8 ± 12.9% in CON and 52.5 ± 18.7% in the HT group. The change from baseline to 8 weeks in %CVCmax was similar between CON and HT (CON: ‐2.6 ± 13.9%, HT: ‐0.7 ± 16.3%, p=0.74). Peak calf blood flow during reactive hyperemia was comparable between groups at baseline (CON: 48.0 ± 24.6 ml/min/100g, HT: 43.8 ± 20.4 ml/min/100g, p=0.76). The change from baseline to 8 weeks in peak calf perfusion was also similar between CON and HT (CON: ‐4.8±21.9 ml/min/100g, HT: ‐2.8±11.0 ml/min/100g, p=0.84).CONCLUSIONEight weeks of home‐based leg HT does not improve leg vascular function in patients with symptomatic PAD.