Phenylephrine-mediated Vasoconstriction Research Articles

Corncob bedding alters fasting blood glucose and vascular function in mice

Rodent husbandry requires careful consideration of environmental factors that may impact colony performance and subsequent physiological studies. Of note, recent reports have suggested corncob bedding is potentially a confounding variable affecting a broad range of organ systems. As corncob bedding may contain digestible hemicelluloses, trace sugars, and fiber, we hypothesized that corncob bedding impacts murine vascular function and overnight fasting blood glucose. Here, we compared mice housed on corncob bedding, which were then fasted overnight on either corncob or ALPHA-dri bedding, a paper cellulose alternative. Male and female mice were used from two non-induced, endothelial-specific conditional knock-out strains (Cadherin 5-CreERT2, floxed hemoglobin alpha 1 [Hba1] or Cadherin 5-CreERT2, floxed cytochrome B5 reductase 3 [CyB5R3]) on a C57BL/6J genetic background. After fasting overnight, initial blood glucose was measured, and mice were anesthetized with isoflurane for measurement of blood perfusion via laser speckle contrast analysis using a PeriMed PeriCam PSI NR system. After a 15-minute equilibration, the mice were injected intraperitoneally with phenylephrine (5 mg/kg) or saline and monitored for changes in blood perfusion. After a 15-minute response period, blood glucose was remeasured post-procedure. Consistently, mice fasted on corncob bedding had higher blood glucose than the ALPHA-dri group. In the CyB5R3 strain, corncob bedding caused a reduction in phenylephrine-mediated vasoconstriction. In the Hba1 strain, phenylephrine-induced vasoconstriction was more variable in the corncob group. Altogether, this work suggests that corncob bedding could be a confounding variable for vascular measurements and fasting blood glucose in mice. To promote scientific rigor and improve reproducibility, bedding type should be included in published methods. NIH R01HL155618 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.

Old cells die hard - sympatholysis and the ageing erythrocyte.

Old cells die hard - sympatholysis and the ageing erythrocyte.

Hyperdynamic circulatory syndrome in a mouse model transgenic for SerpinB3

Introduction and objectivesSerpinB3 is a cysteine protease inhibitor involved in several biological activities. It is progressively expressed in chronic liver disease, but not in normal liver. The role in vascular reactivity of this serpin, belonging to the same family of Angiotensin II, is still unknown. Our aim was to evaluate the in vivo and in vitro effects of SerpinB3 on systemic and splanchnic hemodynamics. Material and methodsDifferent hemodynamic parameters were evaluated by ultrasonography in two colonies of mice (transgenic for human SerpinB3 and C57BL/6J controls) at baseline and after chronic carbon tetrachloride (CCl4) treatment. In vitro SerpinB3 effect on mesenteric microvessels of 5 Wistar-Kyoto rats was analyzed measuring its direct action on: (a) preconstricted arteries, (b) dose–response curves to phenylephrine, before and after inhibition of angiotensin II type 1 receptors with irbesartan. Hearts of SerpinB3 transgenic mice and of the corresponding controls were also analyzed by morphometric assessment. ResultsIn SerpinB3 transgenic mice, cardiac output (51.6±21.5 vs 30.1±10.8ml/min, p=0.003), hepatic artery pulsatility index (0.85±0.13 vs 0.65±0.11, p<0.001) and portal vein blood flow (5.3±3.2 vs 3.1±1.8ml/min, p=0.03) were significantly increased, compared to controls. In vitro, recombinant SerpinB3 had no direct hemodynamic effect on mesenteric arteries, but it increased their sensitivity to phenylephrine-mediated vasoconstriction (p<0.01). This effect was suppressed by inhibiting angiotensin II type-1 receptors. ConclusionsIn transgenic mice, SerpinB3 is associated with a hyperdynamic circulatory syndrome-like pattern, possibly mediated by angiotensin receptors.

Cucurbitacins extracted from Cucumis melo L. (CuEC) exert a hypotensive effect via regulating vascular tone.

As an effective medicine for jaundice in traditional Chinese medicine, Cucumis melo L. has been widely used in China. However, its effect on vascular function is still unclear. In this study, we extracted the compounds of Cucumis melo L., and the major ingredients were identified as cucurbitacins (CuEC, cucurbitacins extracted from Cucumis melo L.), especially cucurbitacin B. We replicated the toxicity in mice by intraperitoneal injection of a high dose of CuEC (2 mg/kg) and demonstrated that the cause of death was CuEC-induced impairment of the endothelial barrier and, thus, increased vascular permeability via decreasing VE-cadherin conjunction. The administration of low doses of CuEC (1 mg/kg) led to a decline in systolic blood pressure (SBP) without causing toxicity in mice. More importantly, CuEC dramatically suppressed angiotensin II (Ang II)-induced SBP increase. Further studies demonstrated that CuEC facilitated acetylcholine-mediated vasodilation in mesenteric arteries of mice. In vitro studies showed that CuEC induced vasodilation in a dose-dependent manner in mesenteric arteries of both mice and rats. Pretreatment with CuEC inhibited phenylephrine-mediated vasoconstriction. In summary, a moderate dose of CuEC reduced SBP by improving blood vessel tension. Therefore, our study provides new experimental evidence for developing new antihypertensive drugs.

Wild blueberry consumption attenuates local inflammation in the perivascular adipose tissue of obese Zucker rats

Perivascular adipose tissue (PVAT) has been shown to play important roles in regulating vascular tone and linking local and systemic vascular inflammation. We examined the impact of PVAT on phenylephrine-mediated vasoconstriction in the aorta of obese Zucker rats (OZR) and their lean littermates (LZR) by comparing aortic rings with or without PVAT. Subsequently we placed OZR and LZR on a control (C) or an 8% wild blueberry (WB) diet and evaluated the effect of WB consumption on such response. PVAT-released adipokine concentrations were also measured as a function of WB diet. Maximal constrictor force (Fmax) in aortic rings without PVAT was significantly lower in OZR-C compared with LZR-C (0.41 ± 0.05 and 0.71 ± 0.06 g, respectively). Following WB diet, Fmax significantly increased in OZR (0.54 ± 0.06 g). In aortas with intact PVAT, Fmax was significantly lower in all groups (0.31 ± 0.06 OZR-C, 0.30 ± 0.05 OZR-WB, 0.29 ± 0.03 LZR-C, and 0.30 ± 0.04 g LZR-WB), but no difference was observed between treatments. PVAT concentrations of monocyte chemoactractant protein 1 (MCP-1), tumor necrosis factor alpha, and adiponectin were significantly higher in OZR compared with LZR (+102%, +108%, and +45%, respectively). Following WB diet, PVAT concentrations of interleukin-8 were significantly lower in both OZR (-37%) and LZR (-30%), while adiponectin concentrations significantly increased in both OZR (+11%) and LZR (+16%). MCP-1 concentrations significantly decreased (-31%) in the PVAT of OZR with the WB diet. WB consumption appears to attenuate local inflammation in PVAT, which may impact systemic vascular inflammation and endothelial function.

Genetic variation in the α1A-adrenergic receptor and phenylephrine-mediated venoconstriction.

There is large interindividual variability and ethnic differences in phenylephrine-mediated vasoconstriction. We tested the hypothesis that genetic variation in ADRA1A, the α1A adrenergic receptor gene, contributes to the variability and ethnic differences. We measured local dorsal hand vein responses to increasing doses of phenylephrine in 64 Caucasians and 42 African-Americans and genotyped for 32 ADRA1A SNPs. The ED50 ranged from 11 to 5442 ng/min, and the Emax ranged from 13.5% to 100%. The rs574647 variant was associated with a trend towards lower logED50 in each race and in the combined cohort (P=0.008). Additionally, rs1079078 was associated with a trend to higher logED50 in each race and in the combined cohort (P=0.011). Neither variant accounted for the ethnic differences in response. None of the ADRA1A haplotypes was associated with the outcomes. In conclusion, ADRA1A variants do not contribute substantially to the marked interindividual variability or ethnic differences in phenylephrine-mediated venoconstriction.

Thiamine deficiency leads to reduced nitric oxide production and vascular dysfunction in rats

Background and aimsThiamine deficiency is a condition that is known to cause damage to the nervous and cardiovascular systems because it interferes with cellular metabolism. It is well known that the control of vascular function is highly dependent on the production of nitric oxide (NO) by NO synthases. Studies exploring the physiological relevance of NO signaling under conditions of thiamine deficiency are scarce. The present study sought to investigate whether chronic metabolic changes would cause alterations in vascular responsiveness. Methods and resultsBy removing thiamine from the diet, we observed a reduced acetylcholine-mediated relaxation and an increased phenylephrine-mediated vasoconstriction in the aortas containing functional endothelium. Removal of the endothelium or the pre-treatment of vessels with l-NAME restored the contractile responses to the level of controls. Conversely, indomethacin did not modify phenylephrine-mediated contractions. We also used carbon microsensors to continually measure NO production in situ while simultaneously measuring the vascular tone. The results revealed a significant decrease in NO production. Western blot analysis showed a decreased expression of the total eNOS in the thiamine-deficient aorta compared to the control. Concentration–response curves for phenylephrine indicated no difference between the control and deficient groups in the presence and absence of SOD or Tyron. The NO donor DEA-NONOate produced a concentration-dependent relaxation response in the endothelium-denuded vessels that did not differ between the control and thiamine-deficient rats. ConclusionThiamine deficiency modulates eNOS-dependent NO production, leading to a decreased vasorelaxation and an increased contractile response in the rat aorta.

Androgen-Sensitive Hypertension Associates with Upregulated Vascular CYP4A12–20-HETE Synthase

Although the mechanism underlying the effect of androgen on BP and cardiovascular disease is not well understood, recent studies suggest that 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE), a primary cytochrome P450 4 (Cyp4)-derived eicosanoid, may mediate androgen-induced hypertension. Here, treatment of normotensive mice with 5α-dihydrotestosterone increased BP and induced both Cyp4a12 expression and 20-HETE levels in preglomerular microvessels. Administration of a 20-HETE antagonist prevented and reversed the effects of dihydrotestosterone on BP. Cyp4a14(-/-) mice, which exhibit androgen-sensitive hypertension in the male mice, produced increased levels of vascular 20-HETE; furthermore, administration of a 20-HETE antagonist normalized BP. To examine whether androgen-independent increases in 20-HETE are sufficient to cause hypertension, we studied Cyp4a12-transgenic mice, which express the CYP4A12-20-HETE synthase under the control of a doxycycline-sensitive promoter. Administration of doxycycline increased BP by 40%, and administration of a 20-HETE antagonist prevented this increase. Levels of CYP4A12 and 20-HETE in preglomerular microvessels of doxycycline-treated transgenic mice approximately doubled, correlating with increased 20-HETE-dependent sensitivity to phenylephrine-mediated vasoconstriction and with decreased acetylcholine-mediated vasodilation in the renal microvasculature. We observed a similar contribution of 20-HETE to myogenic tone in the mesenteric microvasculature. Taken together, these results suggest that 20-HETE both mediates androgen-induced hypertension and can cause hypertension independent of androgen.

Abstract 324: Tumor Necrosis Factor-a (TNF-a) Mediates Microvascular Dysfunction Induced by High-fat Diet and Murine Cytomegalovirus (mCMV) Infection in a Mouse Model

Cardiovascular diseases are mediated by a variety of risk factors, e.g. obesity and infections. Complicated obesity and mCMV each induce microvascular dysfunction in mouse models. However, the impact of mild obesity on microvascular homeostasis and its possible synergism with cytomegalovirus infection remain unclear. We have shown that 8 wks high-fat diet (HFD) increases leukocyte recruitment in cremasteric post-capillary venules, and mCMV accelerates and sustains this response. We hypothesized that HFD and/or mCMV impair phenylephrine-mediated vasoconstriction in arterioles, and that the arteriolar and venular responses are mediated by an imbalance between TNF-α and leptin, vs. adiponectin. Mice were inoculated with mock or mCMV and at 4 wks post-infection (pi) started on HFD or left on normal diet (ND). At 12 wks pi, leukocyte recruitment and arteriolar vasoconstriction were assessed by intravital microscopy. Adiponectin and leptin were measured by ELISA. Some mice were treated with anti-TNF-α antibodies 2 days prior to observation. mCMV infection alone did not alter any parameter when compared to Mock-ND. Arteriolar vasoconstriction to phenylephrine was impaired in both HFD groups vs. Mock-ND mice. TNF-α inhibition partially restored this impaired vasoconstriction. Leukocyte adhesion was increased in both HFD groups vs. ND mice, and was ameliorated by anti-TNF-α antibody treatment in mCMV-HFD, but not Mock-HFD mice. Adiponectin levels in HFD vs. ND groups were slightly increased, and leptin levels were ~5-6-fold higher. Our results suggest that HFD-/+mCMV infection impairs arteriolar vasoconstriction via a TNF-α dependent mechanism. TNF-α independent HFD-induced leukocyte adhesion in venules is changed to a TNF-α dependent pathway by mCMV infection. Increased leptin levels in HFD groups correlate with previous findings linking obesity and increased leptin. Increased adiponectin levels in HFD animals are contrary to responses previously reported for complicated obesity and may represent an initial compensatory role for adiponectin in the response to HFD-induced weight gain and inflammation. However, the roles for leptin and adiponectin require future investigation.

Rapid Aldosterone Signaling and Vascular Reactivity: Relax or Don't Do It

Rapid Aldosterone Signaling and Vascular Reactivity: Relax or Don't Do It

Vascular Insulin-Like Growth Factor-I Resistance and Diet-Induced Obesity

Obesity and type 2 diabetes mellitus are characterized by insulin resistance, reduced bioavailability of the antiatherosclerotic signaling molecule nitric oxide (NO), and accelerated atherosclerosis. IGF-I, the principal growth-stimulating peptide, which shares many of the effects of insulin, may, like insulin, also be involved in metabolic and vascular homeostasis. We examined the effects of IGF-I on NO bioavailability and the effect of obesity/type 2 diabetes mellitus on IGF-I actions at a whole-body level and in the vasculature. In aortic rings IGF-I blunted phenylephrine-mediated vasoconstriction and relaxed rings preconstricted with phenylephrine, an effect blocked by N(G)-monomethyl L-arginine. IGF-I increased NO synthase activity to an extent similar to that seen with insulin and in-vivo IGF-I led to serine phosphorylation of endothelial NO synthase (eNOS). Mice rendered obese using a high-fat diet were less sensitive to the glucose-lowering effects of insulin and IGF-I. IGF-I increased aortic phospho-eNOS levels in lean mice, an effect that was blunted in obese mice. eNOS activity in aortae of lean mice increased 1.6-fold in response to IGF-I compared with obese mice. IGF-I-mediated vasorelaxation was blunted in obese mice. These data demonstrate that IGF-I increases eNOS phosphorylation in-vivo, increases eNOS activity, and leads to NO-dependent relaxation of conduit vessels. Obesity is associated with resistance to IGF-I at a whole-body level and in the endothelium. Vascular IGF-I resistance may represent a novel therapeutic target to prevent or slow the accelerated vasculopathy seen in humans with obesity or type 2 diabetes mellitus.

Phenylephrine-Induced Microvascular Occlusion Syndrome in a Patient With a Heterozygous Factor V Leiden Mutation

Cutaneous microvascular occlusion syndromes (MOS) present with noninflammatory retiform purpura with variable outcomes that are dependent on the severity, duration, and specific underlying cause. Transient cases are often associated with few sequelae, while severe forms such as symmetrical peripheral gangrene may be associated with amputation and death. A middle-aged man developed MOS after exposure to phenylephrine hydrochloride and experienced complete resolution when treatment with the vasopressor was discontinued. Further evaluation detected a previously subclinical heterozygous factor V Leiden mutation. We propose that phenylephrine-mediated vasoconstriction superimposed on an underlying thrombotic predisposition precipitated the transient MOS. The role of vasopressors in the development of cutaneous MOS is well documented in the critical care literature; however, it is underrepresented in the dermatologic literature, and, to our knowledge, there are no reports of phenylephrine use inducing MOS. We hope to raise awareness of the potential role of vasopressor medications in causing MOS.

Chronic alcohol-induced oxidative endothelial injury relates to angiotensin II levels in the rat

The link between chronic alcohol consumption and cardiovascular injury including hypertension is well known. However, molecular mediators implicated with alcohol-induced elevation in blood pressure (BP) remain elusive. The aim of this study was to investigate the relationship of chronic ethanol-induced endothelial injury and elevation in BP with angiotensin II levels in rats. Male Fisher rats were divided into two groups of seven animals each and treated as follows: (1) Control (5% sucrose, orally) daily for 12 weeks and (2) ethanol (4 g kg(-1), orally) daily for 12 weeks. The BP (systolic, diastolic, and mean) was recorded every week. The animals were anesthetized with pentobarbital after 12 weeks; blood and thoracic aorta were isolated and analyzed for aortic reactivity response, angiotensin II levels, and oxidative endothelial injury. The results show that the systolic, diastolic, and mean BP were significantly elevated 12 weeks after ethanol ingestion. The increased BP was related to elevated angiotensin II levels in the plasma and aorta of alcohol treated group compared to control. The aortic NADPH oxidase activity, ratio of oxidized to reduced glutathione (GSSG/GSH) and lipid peroxidation significantly increased, whereas nitric oxide (NO), endothelial NO synthase (eNOS), and vascular endothelial growth factor (VEGF) protein expressions were depressed in alcohol group compared to control. The phenylephrine-mediated vasoconstriction response was not altered, while acetylcholine-mediated vasorelaxation response was depressed in the aorta of ethanol treated rats compared to control. It is concluded that chronic ethanol ingestion induces hypertension which is correlated with elevated tissue angiotensin II levels, activation of NADPH oxidase activity causing endothelial injury, depletion of endothelial NO generating system, and impaired vascular relaxation in rats.

Selective α2-adrenergic properties of dexmedetomidine over clonidine in the human forearm

We tested the hypothesis that dexmedetomidine (Dex) has greater alpha(2)- vs. alpha(1) selectivity than clonidine and causes more alpha(2)-selective vasoconstriction in the human forearm. After local beta-adrenergic blockade with propranolol, forearm blood flow (plethysmography) responses to brachial artery administration of Dex, clonidine, and phenylephrine (alpha(1)-agonist) were determined in healthy young adults before and after alpha(2)-blockade with yohimbine (n = 10) or alpha(1)-blockade with prazosin (n = 9). Yohimbine had no effect on phenylephrine-mediated vasoconstriction but blunted Dex-mediated vasoconstriction (mean +/- SE: -41 +/- 5 vs. -11 +/- 2%; before vs. after yohimbine) more than clonidine-mediated vasoconstriction (-39 +/- 5 vs. -28 +/- 4%; before vs. after yohimbine) (P < 0.02). Prazosin blunted phenylephrine-mediated vasoconstriction (-39 +/- 4 vs. -8 +/- 2%; before vs. after prazosin) but had similar effects on both Dex- (-30 +/- 4 vs. -39 +/- 6%; before vs. after prazosin) and clonidine-mediated vasoconstriction (-29 +/- 3 vs. -41 +/- 7%; before vs. after prazosin) (P > 0.7). Both Dex and clonidine reduced deep forearm venous norepinephrine concentrations to a similar extent (-59 +/- 12 vs. -55 +/- 10 pg/ml; Dex vs. clonidine, P > 0.6); this effect was abolished by yohimbine and blunted by prazosin. These results suggest that Dex causes more alpha(2)-selective vasoconstriction in the forearm than clonidine. The similar vasoconstrictor responses to both drugs after prazosin might be explained by the presynaptic effects on norepinephrine release.

Moderate dietary salt restriction increases vascular and systemic insulin resistance

Our recent studies have indicated that severe salt restriction aggravates vascular insulin resistance in younger normotensive and hypertensive subjects. However, whether the extent of dietary salt restriction commonly advocated adversely affects vascular insulin resistance is unknown. To determine whether moderate dietary salt restriction might affect vascular and systemic sensitivity to insulin, we studied eight subjects after 1 week of a normal sodium diet (235 mEq/day) and 1 week of a moderate salt restriction (75 meq/day). Systemic insulin resistance as assessed by the fasting plasma glucose-to-insulin ratio was aggravated by dietary sodium restriction (normal sodium: 1.2 ± 0.1 mmol/mIU; low sodium 0.6 ± 0.1, P < .05). Salt restriction significantly reduced maximal insulin-mediated vasodilation (normal sodium: 51% ± 5% of maximum nitroglycerin-mediated response; low sodium: 28% ± 6%, P < .01). In contrast, no alterations in nitroglycerin-mediated vasodilation nor phenylephrine-mediated vasoconstriction were noted. These studies demonstrate that moderate salt restriction aggravates both systemic and vascular insulin resistance. This impairment of the vasodilating effect of insulin could be a factor attenuating the blood pressure lowering effect of a low sodium diet.

Vascular alpha-adrenergic responsiveness is reduced in cirrhosis.

Cirrhosis of the liver is associated with altered cardiovascular regulation. Patients with cirrhosis often have decreased total peripheral vascular resistance despite increased sympathetic activity. To determine whether this reduction in effective sympathetic activity may be caused by an alteration in vascular adrenergic responsiveness, we studied nine patients with biopsy-proven cirrhosis and 12 age-matched control subjects. To assess human vascular adrenergic responsiveness, we used dorsal hand vein linear variable differential transformer techniques. Sensitivity for phenylephrine-mediated vasoconstriction was significantly reduced in patients with cirrhosis (median effective dose [ED50] for phenylephrine: cirrhosis, 1514 ng/min; control subjects, 282 ng/min; p = 0.026). In contrast, the effect of isoproterenol did not differ (cirrhosis: 89% +/- 15% of maximal nitroglycerin effect; control subjects 79% +/- 6%; ED50 for isoproterenol: cirrhosis, 38 ng/min; control subjects, 20 ng/min). These studies indicate that vascular alpha-adrenergic responsiveness in patients with cirrhosis is decreased, whereas beta-adrenergic responsiveness remains intact. A selective decrease in vascular alpha-adrenergic responsiveness may contribute to the decreased peripheral vascular resistance in cirrhosis.

Defective venous beta-adrenergic response in borderline hypertensive subjects is corrected by a low sodium diet.

Hypertensive patients have reduced lymphocyte beta-adrenergic responsiveness which is corrected by a low sodium (Na) diet. To determine if this represents a more generalized abnormality in beta adrenoceptor response, we studied beta adrenergic-mediated vasodilation in hand veins of borderline hypertensive subjects and controls. Subjects received a 5-d diet containing high Na/low potassium (K), high Na/high K, or low Na/high K. Venous distension, as evaluated by a linear variable differential transformer, was measured in relation to infusion of phenylephrine followed by isoproterenol and nitroglycerin. On both the high Na/high K and high Na/low K diets, hypertensive subjects had significantly decreased isoproterenol-mediated vasodilation (47% decrease, P less than 0.01 and 36% decrease, P less than 0.01, respectively). On the low Na/high K diet, isoproterenol-mediated vasodilation in hypertensive subjects increased 41% (P less than 0.01) to a level not different from controls. Nitroglycerin-mediated vasodilation was not different in normotensive and hypertensive subjects, nor was it altered with Na intake. Phenylephrine-mediated vasoconstriction did not differ between normotensive and hypertensive groups. Venous beta-adrenergic response correlated with lymphocyte beta adrenoceptor density in normotensive (r = 0.53, P less than 0.005) but not hypertensive subjects. This study demonstrates that beta-adrenergic responsiveness is selectively reduced in peripheral veins of borderline hypertensive subjects, and this is corrected by a low Na diet. In view of our previous findings of reduced lymphocyte beta-adrenergic responsiveness in borderline hypertension, these studies suggest a generalized defect of beta adrenoceptor responsiveness in human hypertension. Further, dietary Na may play an important role in regulating this abnormality.