Tail-cuff Systolic Blood Pressure Research Articles

Tubular deficiency of ABCA1 augments cholesterol- and Na+-dependent effects on systemic blood pressure in male mice.

Dyslipidemia, with changes in plasma membrane (PM) composition, is associated with hypertension, while rising PM cholesterol induces Na+ channel activity. We hypothesize that ablation of renal tubular ABCA1, a cholesterol efflux protein, leads to cholesterol- and Na+-dependent changes in blood pressure (BP). Transgenic mice (TgPAX8rtTA;tetO-Cre/+) expressing a doxycycline (dox)-inducible CRE recombinase were bred with mice expressing floxed ABCA1 to generate renal tubules deficient in ABCA1 (ABCA1FF). Tail-cuff systolic BP (SBP) was measured in mice on specific diets. Immunoblotting was performed on whole and PM protein lysates of kidney from mice completing experimental diets. Cortical PM of ABCA1FF showed reduced ABCA1 (60 ± 28%; n = 10, P < 0.05) compared with wild-type littermates (WT; n = 9). Tail-cuff SBP of ABCA1FF (n = 11) was not only greater post dox, but also during cholesterol or high Na+ feeding (P < 0.05) compared with WT mice (n = 15). A Na+-deficient diet abolished the difference, while 6 wk of cholesterol diet raised SBP in ABCA1FF compared with mice before cholesterol feeding (P < 0.05). No difference in α-ENaC protein abundance was noted in kidney lysate; however, γ-ENaC increased in ABCA1FF mice versus WT mice. In kidney membranes, NKCC2 abundance was greater in ABCA1FF versus WT mice. Cortical lysates of ABCA1FF mouse kidneys expressed less renin and angiotensin I receptor than WT mouse kidneys. Furosemide injection induced a greater diuretic effect in ABCA1FF (n = 7; 45.2 ± 8.7 µL/g body wt) versus WT (n = 7; 33.1 ± 6.9 µL/g body wt; P < 0.05) but amiloride did not. Tubular ABCA1 deficiency induces cholesterol-dependent rise in SBP and modest Na+ sensitivity of SBP, which we speculate is partly related to Na+ transporters and channels.NEW & NOTEWORTHY Cholesterol has been linked to greater Na+ channel activity in kidney cells, which may predispose to systemic hypertension. We showed that when ABCA1, a protein that removes cholesterol from tissues, is ablated from mouse kidneys, systemic blood pressure is greater than normal mice. Dietary cholesterol further increases blood pressure in transgenic mice, whereas low dietary salt intake reduced blood pressure to that of normal mice. Thus, we speculate that diseases and pharmaceuticals that reduce renal ABCA1 expression, like diabetes and calcineurin inhibitors, respectively, contribute to the prominence of hypertension in their clinical presentation.

Differences and the impact of G protein-coupled estrogen receptor deletion in the vascular and renal response to aldosterone

We recently showed that the G protein-coupled estrogen receptor (GPER) protects female mice from arterial stiffening, an independent predictor of cardiovascular mortality. Previous work indicates that GPER may directly bind aldosterone and/or dimerize with the mineralocorticoid receptor. Therefore, we hypothesized that GPER may promote aldosterone-induced renal and vascular effects, particularly in male animals where less estrogen is available to activate GPER. Male (M) and female (F) wildtype (wt) and global GPER knockout (ko) mice were used between 6-7 months of age. Aldosterone was delivered to all mice subcutaneously via osmotic mini pumps at a dose of 600 μg/kg/day and drinking water was replaced with saline for 28 days. At the end of the study, tail-cuff systolic blood pressure (SBP) and metabolic cage data were collected. Data were analyzed by 2-way ANOVA followed by Sidak’s test and correlation analysis. In basal conditions, GPER ko increased systolic SBP in males but not females. After aldosterone-salt treatment, SBP was similar in Mwt versus Mko but was significantly higher in Fko versus Fwt (Pinteraction=0.002; 148 ± 12 vs. 108 ± 2 mmHg; P&lt;0.001). Similarly, proteinuria was similar in males but greater in Fko than Fwt (Pinteraction=0.01; 6.0 ± 1.5 vs. 2.4 ± 0.4 mg/day; P=0.04), indicating greater kidney injury. In summary, GPER deletion in females revealed enhanced blood pressure and renal damage in response to an aldosterone-salt challenge. These findings do not support a role for GPER in promoting the impact of aldosterone on vascular and renal damage in either sex. In contrast, GPER protected female mice from the negative impact of aldosterone-salt on blood pressure and kidney function. More studies are needed to understand the interactions of GPER and aldosterone in the kidney of both males and females. This work was supported by the National Institutes of Health (HL133619 and AG071746 to SL, HL155841 to BO) and the American Heart Association (BV and IK) 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.

Abstract 13462: Assessment of the Physiological and Pathological Structural Differences Along the Aorta in a Rat Model of Metabolic Syndrome

Introduction: Vascular geometry may vary along the aortic length in normal and chronic disease conditions such as metabolic syndrome. Aim: This study investigated regional structural changes in the aorta in a rodent model of metabolic syndrome, the high-fat diet streptozotocin-induced diabetes mellitus (HFD-D). Methods: Four-week-old male Wistar albino rats received a control diet (CD) or high fat diet (HFD) for 10 weeks. On week 6, 40 mg/kg streptozotocin and its buffer were injected intraperitoneally into the HFD and CD groups, respectively. Glucose and insulin tolerance tests (GTT and ITT) and tail-cuff systolic blood pressure (SBP) were measured. At the end of the study, rats were euthanized, and the thoracic and abdominal aortic segments collected for histomorphometric analysis of aortic media thickness, medial cross-sectional area (CSA), elastic lamellae number, interlamellar spacing, collagen density and lipid deposit density. Results: HFD-D rats showed elevated GTT, ITT and SBP. Abdominal aortic segments of both CD and HFD-D rats showed smaller media thickness and CSA, lower elastin lamellae number and higher collagen density compared with the thoracic segments, suggestive of physiological rather than pathological structural differences in both groups. Elastin interlamellar spacing and lipid plaque deposits were higher in the abdominal aorta of the HFD-D relative to controls, indicating that early vascular pathological changes favor the abdominal aorta in HFD-D rats. Conclusions: In this disease model of metabolic syndrome, vascular structural changes are differentially expressed along the aorta, with pathological features limited to the abdominal rather than the thoracic aorta. These structural abnormalities may underlie the elevated blood pressure seen in this model and potential progression to hypertensive cardiovascular disease.

DIFFERENTIAL EXPRESSION OF VASCULAR DYSFUNCTION OF SMALLER DIAMETER ARTERIES IN A RODENT MODEL OF METABOLIC SYNDROME

Objective: Metabolic syndrome, driven by obesity and diabetes, is a major contributor to cardiovascular disease. While large arteries vascular dysfunction is a well-documented phenomenon of metabolic syndrome, vascular disease of smaller diameter arteries, which are key contributors to peripheral vascular resistance and blood pressure control, remains uncertain. Using in-vitro organ-bath preparation, this study, therefore, investigated functional responses of the superior mesenteric and right iliac arteries in a high fat diet (HFD)/streptozotocin-induced diabetes mellitus rat model. Design and method: Five-week-old male Wistar Albino rats (n = 24) were fed with either HFD (45 kcal% fat) or control diet (10 kcal% fat) for 10 weeks. At 10 weeks of age, 40 mg/kg streptozotocin and saline were injected intraperitoneally into the HFD and control groups, respectively. Results: Diabetic HFD rats displayed a time-dependent increase (p &lt; 0.01) in water intake, urine output, fasting blood glucose and tailcuff systolic blood pressure compared to controls (154 ± 6 vs. 110 ± 4 mmHg). Both mesenteric and iliac vasoconstrictor responses (N/g) to norepinephrine (1E-9 – 3E-5 M), but not to the depolarizing signals of high potassium (5 – 120 mM), were greater (p &lt; 0.01) in the HFD group relative to controls. Mesenteric, but not iliac, endothelium-dependent vasorelaxation to acetylcholine (1E-10 – 1E-5 M) was blunted (p &lt; 0.05) in the HFD rats compared with controls. In contrast, mesenteric and iliac endothelium-independent vasorelaxation responses to sodium nitroprusside (1E-11 – 1E-6 M) remained comparable between groups. Conclusions: Vascular functional responses in smaller diameter arteries are differentially expressed in metabolic syndrome, demonstrating upregulated vasoconstriction to adrenergic stimuli and/or impaired endothelium-dependent relaxation. These vascular abnormalities align with those previously described in larger arteries and could therefore further promote the development of cardiovascular disease in metabolic syndrome.

Regional functional and structural abnormalities within the aorta as a potential driver of vascular disease in metabolic syndrome.

What is the central question of this study? Is aortic dysfunction, a significant contributor to cardiovascular disease in metabolic syndrome, expressed uniformly across both the thoracic and abdominal aorta? What is the main finding and its importance? Our study shows that, in the setting of metabolic syndrome, functional and structural deficits in the aorta are differentially expressed along its length, with the abdominal portion displaying more extensive vascular abnormalities. It is, therefore, likely that early interventional strategies targeting the abdominal aorta might alleviate cardiovascular pathologies driven by the metabolic syndrome. The extent of vascular dysfunction associated with metabolic syndrome might vary along the length of the aorta. In this study, we investigated regional functional and structural changes in the thoracic and abdominal aorta of a rat model of metabolic syndrome, namely, high-fat diet (HFD) streptozotocin-induced diabetes mellitus (HFD-D). Four-week-old male Wistar albino rats were fed with either HFD or control diet (CD) for 10weeks. At week6, 40mg/kg streptozotocin and its vehicle were injected i.p. into HFD and CD groups, respectively. At the end of the feeding period, rats were euthanised and aortic segments collected for assessment of vascular functional responses and histomorphometry. Tail-cuff systolic blood pressures (154±6vs. 110±4mmHg) and areas under the curve for oral glucose and i.p. insulin tolerance tests were greater in HFD-D versus CD rats. Abdominal aortic vasoconstriction in response to noradrenaline and KCl was greater in HFD-D compared with CD rats. Thoracic vasoconstrictor responses to noradrenaline, but not KCl, were greater in the HFD-D group. Abdominal, but not thoracic, endothelium-dependent vasorelaxation in response to acetylcholine was blunted in HFD-D relative to CD rats; however, nitric oxide-dependent vasorelaxation in HFD-D rats was impaired in both thoracic and abdominal segments. The abdominal aorta of HFD-D rats showed deranged interlamellar spacing and increased lipid plaque deposition. In conclusion, vascular dysfunction in metabolic syndrome is expressed differentially along the length of the aorta, with the abdominal aorta exhibiting increased susceptibility to vasoconstrictors and greater deficits in endothelium-dependent relaxation. These vascular functional abnormalities could potentially underlie the development of hypertensive cardiovascular disease associated with the metabolic syndrome.

Cell‐based hormone therapy prevents diastolic dysfunction after estrogen loss in the Spontaneously Hypertensive Rat (SHR)

Introduction. Preclinical left ventricular diastolic dysfunction (LVDD) is a forerunner to heart failure with preserved ejection fraction, which is seen more often in older women than men of the same age. While hormone therapy plays an important role in the management of vasomotor and genitourinary symptoms experienced by many women during the menopausal transition, its efficacy with regard to maintenance of cardiac structure and function and prevention of LVDD disease progression with aging has not been tested due to the concern for off‐target health risks (e.g., cancer, blood clots). We developed a cell‐based hormone therapy (cHT) approach that recapitulates native cell–cell interactions between ovarian granulosa and theca cells in a 3D bioengineered construct to mimic the dynamic release of sex hormones into the circulation. Our first report in ovariectomized rats shows that ovarian constructs are able to ameliorate various somatic adverse effects of hormone deficiency (e.g. bone loss). To extend these findings to cardiac health, we sought to determine the efficacy of cHT in preserving cardiac diastolic function after estrogen loss using a hypertensive rodent model.Methods14 SHR females underwent bilateral ovariectomy (OVX) while 5 SHRs received sham surgery at 12 weeks of age; 8 weeks post‐surgery, OVX rats were randomized (n=4–5/group) to vehicle, cHT, or pharmacologic hormone therapy (pHT: E2 (10mg/kg/day) and P4 (2mg/kg/day) subcutaneous pellets) and compared to gonad‐intact rats treated with vehicle (VEH). Body weights and tail cuff systolic blood pressure (SBP) were measured biweekly. Following 10 weeks of treatment, rats were lightly anesthetized (isoflurane) for Doppler measures of diastolic function. Data were analyzed by one‐way ANOVA. P&lt;0.05 was significant.ResultsOVX rats, irrespective of treatment, had higher body weights when compared to sham (P&lt;0.001). Uterine atrophy by OVX was minimized by pHT and cHT, reflecting modest E2‐related effects (Figure A). SBP increased progressively over time (P&lt;0.01), without overt differences across treatment groups. Even so, both cHT and pHT prevented adverse OVX‐related effects on myocardial relaxation (e') and Doppler‐derived filling pressures (E/e') when compared to vehicle (Figures B, C).ConclusionThese data show that novel cell‐based hormone therapy is effective in preventing diastolic dysfunction from surgically‐induced menopause in the SHR. Additional studies are underway to determine cHT’s long‐term (6 months) treatment efficacy in middle‐to‐advanced aged OVX rats.Support or Funding InformationNIH AG061588Figure 1

Abstract 40: Time Course of Cerebral Small Vessel Disease Lesions and Sensory Motor Changes in Spontaneously Hypertensive Stroke Prone Rats

Introduction: Animal models of human cerebral small vessel disease (CSVD) are important for the study of the disease underlying mechanisms and testing therapeutic interventions. Spontaneusly Hypertensive Rats - Stroke Prone (SHRSP) are used as an animal model of human CSVD. However, there is a lack of data regarding the time course of cognitive and motor impairment. Methods: Male age-matched SHRSP and Wistar Kyoto rats (WKY) were studied. Sensorimotor testing (open field test) and tail-cuff systolic blood pressure (SBP) measurements (Visitech Systems, Inc.) were performed weekly starting from 6 until 24 weeks of age. Brain MRI at 7 and 24 weeks was acquired using a 9.4T MRI system. Brain histology was completed at the same time points. Statistical analysis was performed using a linear mixed model with repeated measurements. P&lt; 0.05 was considered significant. Results: 20 SHRSP and 20 WKY male rats were studied. 10 per group were euthanized following brain MRI at 7 weeks and the rest were followed until 24 weeks. SHRSP weighed on average 30 grams less than WKY throughout the study (P=0.0003). At 7 weeks SBP was not different (WKY 106.6±5.4 vs SHRSP 120.8±5.4, P=0.06). SHRSP started to develop hypertension at 9-12 weeks and maintained hypertension until 24 weeks (average group difference across time P&lt;0.0001; SBP at 21 weeks WKY 134.8±5.4 vs SHRSP 168.9±5.4, P&lt;0.0001). Sensorimotor testing showed higher total distance travelled (TDT) at 7 weeks in SHRSP that trended down with ageing. Both groups became similar at 21 weeks (TDT: at 7 weeks WKY 3.78±1.3 vs SHRSP 7.8±1.3, P =0.037; at 21 weeks: WKY 4±1.3 vs SHRSP 4.4±1.3, P=0.83; average group difference across time P=0.014). Brain MRI was normal at 7 weeks, but small white matter hyperintensities were seen at 24 weeks. Brain Histology showed normal histology on hematoxylin &amp; eosin staining at 7 weeks in both groups, while at 24 weeks SHRSP showed CSVD histopathological changes including microbleed formation, homeostasis and vascular hyalinosis. Conclusions: SHRSP develops hypertension, sensorimotor deficits and CSVD pathology as they age suggesting their utility as human CSVD model. Intervention time points should be selected carefully in future therapeutic drug interventions.

Oxidative stress induced by prenatal LPS leads to endothelial dysfunction and renal haemodynamic changes through angiotensin II/NADPH oxidase pathway: Prevention by early treatment with α-tocopherol

We investigated whether hypertension induced by maternal lipopolysaccharide (LPS) administration during gestation is linked to peripheral vascular and renal hemodynamic regulation, through angiotensin II → NADPH-oxidase signalling, and whether these changes are directly linked to intrauterine oxidative stress. Female Wistar rats were submitted to LPS, in the absence or presence of α-tocopherol during pregnancy. Malondialdehyde in placenta and in livers from dams and foetuses was enhanced by LPS. Tail-cuff systolic blood pressure (tcSBP) was elevated in the 16-week-old LPS offspring. Renal malondialdeyde and protein expression of NADPH oxidase isoform 2 were elevated in these animals at 20 weeks of age. Maternal α-tocopherol treatment prevented the elevation in malondialdehyde induced by LPS on placenta and livers from dams and foetuses, as well as prevented the elevation in tcSBP and the elevation in renal malondialdehyde in adult life. LPS offspring presented impairment of endothelium-dependent relaxation in aorta and mesenteric rings, which was blunted by angiotensin type 1 receptor (AT1R) blockade and NADPH oxidase inhibition. At age of 32 weeks, renal hemodynamic parameters were unchanged in anaesthetised LPS offspring, but angiotensin II infusion led to an increased glomerular filtration rate paralleled by filtration fraction elevation. The renal haemodynamic changes provoked by angiotensin II was prevented by early treatment with α-tocopherol and by late treatment with NADPH oxidase inhibitor. These results point to oxidative stress as a mediator of offspring hypertension programmed by maternal inflammation and to the angiotensin II → NADPH oxidase signalling pathway as accountable for vascular and renal dysfunctions that starts and maintains hypertension.

Dietary supplementation of vitamin D prevents the development of western diet-induced metabolic, hepatic and cardiovascular abnormalities in rats.

The western diet high in fat and fructose may cause metabolic disorders and cardiovascular diseases. To evaluate whether long-term daily vitamin D3 supplementation prevents hepatic steatosis and cardiovascular abnormalities and restores insulin sensitivity caused by fat diet in rats without vitamin D deficiency. Three groups of rats were fed for 6 months with standard diet (SD), western diet (WD) or WD containing 23 IU/day/rat vitamin D3, respectively. Tail-cuff systolic blood pressure (SBP)measurements in conscious rats and transthoracic echocardiography were performed in basal condition, and after 3 and 6 months of diet. Hepatic steatosis and myocardial fibrosis were assessed in liver and cardiac tissues using standard methods. Serum insulin and 25(OH)D3 concentrations were determined using rat-specific ELISA kits. Insulin resistance was determined according to the homeostasis model assessment of insulin resistance (HOMA-IR) method. Sixty-one per cent of hepatocytes in WD rats had steatotic vacuoles compared with just 27% in rats on a WD plus vitamin D3 (p < 0.05).HOMA-IR was reduced in rats with vitamin D supplementation compared with WD alone (19.4 ± 5.2 vs 41.9 ± 8.9, p < 0.05). Rat blood pressure and left ventricular mass were both reduced by vitamin D3 supplementation. In animal models of liver and cardiovascular metabolic damage, the supplementation of vitamin D3 shows liver and cardio-protective effects.

Abstract P228: Chronically Enhanced Fructose Intake Induces Salt Sensitive Hypertension in Mice and Increases NKCC2 Phosphorylation

High fructose consumption is implicated in hypertension and renal damage in humans. The mechanisms for the renal effects of fructose are not clear. In normal rats, a high fructose diet (20%) does not increase blood pressure, but rapidly (one week) induces a salt sensitive increase in blood pressure. NaCl reabsorption by the thick ascending limb (TAL) is mediated by the NKCC2 cotransporter. Higher NKCC2 activity is involved in salt sensitive hypertension, and its phosphorylation is increased by fructose in rats. We hypothesized that high fructose (20% drinking water), would induce NKCC2 phosphorylation and induce salt sensitive hypertension in normal C57/Bl6J mice. To test this, mice were given 20% fructose in drinking water and after two weeks they were treated for 10 more weeks with either fructose alone or fructose plus 4% Na diet. Tail cuff systolic blood pressure (SBP) was measured after 3 weeks of training. Total NKCC2 expression, GAPDH and NKCC2 phosphorylation at Thre96/101 (P-NKCC2) were measured by Western blot in freshly isolated TALs. Baseline SBP was 112 ± 3 mmHg. A transient increase to 125± 4 mmHg ( p &lt;0.05) was observed after 1 week on fructose which later decreased to 119 ± 3 mmHg ( p =0.14) by week 2. At the end of week 2, high salt chow was added. BP remained normal for 3 weeks and then increased to 137 ± 11 mmHg ( p &lt;0.05) by week 4 on high salt, but not in fructose alone mice. After 10 weeks SBP remained elevated in the fructose plus high salt diet group (124 ± 3 vs 110 ± 5 mmHg; p &lt;0.05). Water intake and urine volume was similar between the two high fructose groups. After 10 weeks, fasting glucose was higher in all mice with fructose (fructose + HS: 231± 8, fructose: 218 ± 7, normal diet: 122 ± 4 mg/dL, p &lt;0.001). A fructose diet increased P-NKCC2 by 248 ± 82% (n=5, p &lt;0.01) by one week and by 61 ± 21% ( p &lt;0.05) at week 12. The combination of high-fructose high salt diet increased P-NKCC2 by 226 ± 75% ( p &lt;0.05) at 12 weeks. Transcriptome profiling of isolated mouse TALs showed that 20% fructose (7 days) increased the expression of genes upstream of the SPAK and AMPK pathway. We conclude that 20% fructose in drinking water leads to a salt dependent increase in SBP, which appears to occur after mice develop abnormalities in glucose metabolism.

OP.1C.01] HIGH SALT DIET INCREASES AORTIC STIFFNESS AND PRESSURE PULSE AMPLIFICATION IN RAT

Objective: High salt consumption is associated with increased blood pressure and vascular changes in humans. This association is confounded by other lifestyle factors that could equally influence cardiovascular function. This study examines effects of high salt diet on aortic function in a controlled animal study. Design and method: Sprague-Dawley rats were fed either high salt (8% sodium chloride, n = 6) or normal chow (0.26% sodium chloride, n = 5) from weaning. Body weight (BW), nose-to-rump length, tail-cuff systolic blood pressure (SBP), water and food intake, and urine output were measured. At 14 to 17 weeks, rats were anaesthetised and thoracic and abdominal aortic pressure (invasive solid-state catheters) recorded over a physiological mean arterial pressure (MAP) range (60 to 150 mmHg, induced via intra-venous infusion of phenylephrine and sodium nitroprusside, 30 μg/kg/min). Aortic pulse wave velocity (aPWV) and thoracic to abdominal aortic pulse pressure amplification (PPA) were calculated. Left ventricular (LV) and kidney mass were recorded post-mortem. Results Results: High salt diet rats had lower BW (average across all age: 451 ± 57 g, control 498 ± 68 g, p = 0.03), body mass index (0.79 ± 0.08 g/cm2, control 0.82 ± 0.10 g/cm2, p < 0.001) and kidney mass (kidney/BW 0.50 ± 0.09%, control 0.39 ± 0.05%, p = 0.01) without LV hypertrophy (LV/BW 0.24 ± 0.04%, control 0.22 ± 0.03%, p = 0.16). Food intake was similar (high salt 20 ± 3 g/day, control 19 ± 5 g/day, p = 0.36). High salt diet rats drank more (65 ± 10 ml/day, control 22 ± 6 ml/day, p < 0.001) with correspondingly higher urine output (55 ± 9 ml/day, control 15 ± 6 ml/day p < 0.001); conscious SBP was greater (125 ± 12 mmHg, control 117 ± 13 mmHg, p < 0.05). High salt diet resulted in higher aPWV (high salt aPWV across MAP range 60 to 150 mmHg, 4.3 ± 0.2 to 5.4 ± 0.2 m/s, control 3.6 ± 0.3 to 3.9 ± 1.1 m/s, p < 0.001 at each 5 mmHg MAP interval). PPA was greater in high salt diet rats (high salt PPA across MAP range 60 to 150 mmHg, 0.78 ± 0.04 to 1.53 ± 0.27, control 0.62 ± 0.14 to 1.25 ± 0.17, p < 0.001 at each 5 mmHg MAP interval). Conclusions: A high salt diet induced moderately higher arterial blood pressure, greater aortic stiffness and higher PPA, indicating marked changes in transmission characteristics of the aorta, including altered stiffness gradient across the aorta and changed peripheral wave reflection characteristics.

The Effect of Alpha-Lipoic Acid on Mitochondrial Superoxide and Glucocorticoid-Induced Hypertension

Aims. To examine the effect of alpha-lipoic acid, an antioxidant with mitochondrial superoxide inhibitory properties, on adrenocorticotrophic hormone- (ACTH-HT) and dexamethasone-induced hypertensions (DEX-HT) in rats and if any antihypertensive effect is mediated via mitochondrial superoxide inhibition. Methods. In a prevention study, rats received ground food or alpha-lipoic-acid-laced food (10 mg/rat/day) for 15 nights. Saline, adrenocorticotrophic hormone (ACTH, 0.2 mg/kg/day), or dexamethasone (DEX, 10 μg/rat/day) was injected subcutaneously from day 5 to day 11. In a reversal study, rats received alpha-lipoic-acid-laced food 4 days after commencement of saline or DEX. Tail-cuff systolic blood pressure (SBP) was measured second daily. Kidney mitochondrial superoxide was examined using (MitoSOX) Red (MitoSOX) via flow cytometry. Results. SBP was increased by ACTH (P < 0.0005) and DEX (P < 0.0005). Alpha-lipoic acid alone did not alter SBP. With alpha-lipoic acid pretreatment, SBP was increased by ACTH (P′ < 0.005) but not by DEX. Alpha-lipoic partially prevented ACTH-HT (P′ < 0.0005) and fully prevented DEX-HT (P′ < 0.0005) but failed to reverse DEX-HT. ACTH and DEX did not increase MitoSOX signal. In ACTH-hypertensive rats, high-dose alpha-lipoic acid (100 mg/rat/day) did not decrease SBP further but raised MitoSOX signal (P < 0.001), suggesting prooxidant activity. Conclusion. Glucocorticoid-induced hypertension in rats is prevented by alpha-lipoic acid via mechanisms other than mitochondrial superoxide reduction.

Abstract 60: Reduced Macrophage-dependent Inflammation Improves Endothelial Function and Vascular Remodeling, Oxidative Stress and Inflammation in a Model Of Endothelin-1 Induced Vascular Injury

Background: Transgenic mice with endothelium specific preproendothelin-1 overexpression (eET-1) exhibit endothelial dysfunction and vascular remodeling, oxidative stress and inflammation independently of hemodynamic effects. However, it is unclear whether vascular inflammation is causally implicated in adverse vascular effects of endothelin-1 (ET-1). We hypothesized that ET-1-induced vascular injury is decreased in a model of reduced macrophage-dependent inflammation, macrophage colony stimulating factor ( mCsf ) mice heterozygote for the osteopetrosis (Op) mutation. Methods and Results: Wild type (WT), eET-1, mCsf Op/+ and eET-1/ mCsf Op/+ mice were studied. There was no difference in tail-cuff systolic blood pressure between groups. Endothelial function and vascular structure were determined on a pressurized myograph. Endothelium-dependent relaxation in response to acetylcholine was similar in eET-1 and eET-1/ mCsf Op/+ . However, in the presence of L-NAME, the magnitude of NO-independent relaxation was greater in eET-1/ mCsf Op/+ compared to eET-1 (72.4±6.7% vs. 40.8±14.4%, P &lt;0.001). Media-to-lumen ratio was greater in eET-1 than WT (0.13±0.01 vs. 0.08±0.01, P &lt;0.01) and unchanged in eET-1/ mCsf Op/+ (0.10±0.01). Media cross-sectional area (μm 2 ) was greater in eET-1 than WT (13521±2106 vs. 8112±381, P &lt;0.05) and unchanged in eET-1/ mCsf Op/+ (8966±1125). Dihydroethidium staining revealed that reactive oxygen species production in aorta was 4-fold higher in eET-1 than WT ( P &lt;0.01) and unchanged in eET-1/mCsf Op/+ . Aortic monocyte/macrophage infiltration was increased 2.6-fold in eET-1 ( P &lt;0.01) and tended to decrease by 45% in eET-1/mCsf Op/+ compared to WT. Conclusion: Reduction of macrophage-dependent inflammation in mice overexpressing ET-1 in endothelium results in improved vascular relaxation and reduced vascular remodeling, oxidative stress and inflammation, providing evidence for a role of macrophages and innate immunity in ET-1-induced vascular damage.

Discrepant Regulation of QT (QTc) Interval Duration by Calcium Channel Blockade and Angiotensin Converting Enzyme Inhibition in Experimental Hypertension

Antihypertensive treatment may reduce prolonged QT duration in hypertension. Generally, the reductions of blood pressure and/or of cardiac mass are believed to be the responsible factors. However, drugs are not equivalent in QT modulation despite similar antihypertensive and antihypertrophic action. We investigated the effect of a calcium channel blocker, lacidipine and an angiotensin-converting enzyme inhibitor, enalapril on QT duration in rats. Normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were treated with lacidipine (at the dose of 1.5 mg/kg per day for WKY and 3 mg/kg per day for SHR) or enalapril (5 mg/kg per day for WKY and 10 mg/kg per day for SHR) during 8 weeks. Tail-cuff systolic blood pressure (sBP), left ventricular weight (LVW), vascular function of isolated aorta and mesenteric artery and duration of QT (and QTc) interval on Frank electrocardiograms were evaluated. As expected, untreated SHR showed elevated sBP, impaired vascular reactivity, increased LVW and prolonged QT when compared with WKY (p < 0.05). After treatment, both agents markedly improved vascular reactivity and reduced sBP in SHR (p < 0.05). Additionally, enalapril reduced LVW in both hypertensive (by 17%; p < 0.05) and normotensive rats (by 13%; p < 0.05) and, consequently, corrected QT duration in SHR. Interestingly, lacidipine also reduced LVW in SHR (by 9%; p < 0.05), but without influence on prolonged QT. Moreover, lacidipine had no effect on LVW in WKYs but prolonged their QT interval (by 10%; p < 0.05). In conclusion, lacidipine did not reverse a progressive prolongation of QT in SHR, despite sBP lowering and LVW reduction. Thus, the lowering of blood pressure and/or reduction of LVW are not sufficient per se to normalize ventricular repolarization in hypertensive cardiac disease. More likely, modulation of QT prolongation by antihypertensive drugs is a function of their complex action on blood pressure, vascular function, cardiac mass and on reflex neurohumoral activation.

Cardiac remodeling and function following exercise and angiotensin II receptor antagonism

The purpose of this study was to test the impact of chronic exercise training combined with selective angiotensin II receptor (AT1) antagonism on systolic blood pressure (SBP) and the left-ventricular pressure-volume relationship in normotensive, non-infarcted rat hearts. Wistar rats (N=19) were randomly assigned to either a sedentary control group (N=8) or an exercise-trained group (N=11). Losartan was administered to individually caged rats via the drinking water (10mg/kg/d). Exercise training consisted of running on a motorized driven treadmill for 6weeks at 30m/min, 60min/day, 5 days/week. Tail cuff SBP was measured weekly. Left ventricular performance was assessed in an ex vivo Langendorff isovolumic mode. One week of losartan treatment significantly reduced SBP in both groups by 13% relative to baseline (P<0.05). SBP was lower in exercise-trained animals versus sedentary animals in the later weeks of the protocol (P<0.05) Body weight was significantly lower in exercise-trained animals versus sedentary animals, but heart weight, heart to body weight ratio, atrial weight, and absolute left ventricular mass and length were similar between groups. The LV systolic pressure-volume relationship (PV) and systolic elastance were significantly greater in exercise-trained animals versus sedentary controls (P<0.05). The left ventricular end-diastolic PV and diastolic stiffness were similar between exercise-trained and sedentary animals. These data suggest that chronic aerobic exercise training can improve the Starling response in the presence of AT1 receptor blockade without altering absolute cardiac size.

Regulation of angiotensin-converting enzyme 2 and Mas receptor by Ang-(1–7) in heart and kidney of spontaneously hypertensive rats

Inter-regulation between components of the renin-angiotensin system is common, but little is known about the direct regulatory effects of Ang-(1-7) on expression of tissue ACE2 and the Mas receptor. Eighteen male spontaneously hypertensive rats (SHR) and 20 normotensive Wistar-Kyoto rats were randomly allocated to four groups of 9-10 rats each and received either 24 µg/kg per hour of Ang-(1-7) in saline or saline alone (5 ml/h) by infusion for 14 consecutive days. Tail-cuff systolic blood pressures were recorded and ACE2 and Mas expression was measured using quantitative real-time PCR (QRT-PCR) and Western blotting. Cardiac and renal ACE2 mRNA was decreased in SHR. Although having no effects on blood pressure, Ang-(1-7) down-regulated cardiac ACE2 mRNA in normotensive rats (1.80 ± 0.27 vs. 5.89 ± 0.62, p < 0.05) but did not change renal ACE2. Ang(1-7) down-regulated cardiac Mas mRNA of Wistar rats only (2.50 ± 0.44 vs. 8.10 ± 1.33, p < 0.05), and renal Mas mRNA of SHR receiving Ang-(1-7) was decreased (0.44 ± 0.09 vs. 1.00 ± 0.17, p < 0.05). Results from Western blot tests were consistent with those from QRT-PCR tests. These results suggest organ-specific regulation of local ACE2 and Mas expression by continuous infusion of Ang-(1-7) which did not alter blood pressure of either SHR or Wistar rats.

High Tail-Cuff Blood Pressure in Mice 1 Week After Shipping: The Need For Longer Acclimation

For vendor-derived mice, an acclimation period of 1 week is usually recommended before blood pressure measurements are started. However, we observed hypertension in wild-type vendor-derived mice 1 week after shipping. The index group (n = 12, BALB/c, age 3 months, weight 26-28 g) was shipped overnight (by truck, duration 13 h). Tail-cuff systolic blood pressures (SBPs) of the index group were compared to two control groups (n = 6/group), one acclimated for 3 weeks after shipping, and one derived from an in-house colony. One week after shipping, SBP in the index group was 141 ± 3 mm Hg. Because this was much higher than reported previously for this strain, acclimation was prolonged. Six weeks after shipping, SBP had fallen to 124 ± 3 mm Hg (P < 0.005). During this time, heart rate also fell from 721 ± 15 to 665 ± 13 bpm (P < 0.01). SBP in the two control groups was also lower than in the index group 1 week after shipping, including the group acclimated for 3 weeks (129 ± 3 vs. 141 ± 3 mm Hg, P < 0.05) and the in-house mice (124 ± 3 vs. 141 ± 3 mm Hg, P < 0.005). Vendor-derived mice are hypertensive 1 week after shipping, become normotensive after 3 weeks, but do not return to levels of in-house mice until after 6 weeks. Acclimation periods of at least 3 weeks are required when measuring blood pressure in mice.

Activation of TRPV1 inhibits angiotensin II induced vasoconstriction in mice

Objective We investigated the long-term effect of capsaicin, a transient receptor potential vanilloid 1 (TRPV1) agonist, on vascular reactivity in C57BL/6J mice. Design and methods Two-month-old male C57BL/6J mice were fed with regular diet (control group, n=12) and capsaicin-containing diet (capsaicin group, n=12). Tail-cuff systolic blood pressure (SBP) was examined at the baseline and at the end of the intervention. After 6-month treatment with capsaicin, invasive carotid artery blood pressure and heart rate were measured, and the aortic contraction was examined using isometric myograph (Danish Myotech Technology, Denmark). Plasma levels of renin, angiotensinII (AngII) and aldosterone were determined. Vascular smooth muscle cells (VSMCs) were obtained from thoracic aorta of mice and cultured by tissue explant method. AngiotensinII type 1 receptor (AT1R) protein expression was detected by western blotting. Cytosolic calcium level was detected in VSMCs using the fluorescent dye technique. Results SBP, invasive carotid artery blood pressure and heart rate had no difference between two groups. Norepinephrine-induced contraction response in thoracic aorta was not different; while AngII-induced contraction of aortic ring was lower in the capsaicin group than control group (P<0.05). Plasma levels of renin, AngII and aldosterone were not different between the two groups. Treatment with capsaicin significantly decreased AT1R protein expression and AngII-induced calcium entry in cultured VSMCs (P<0.05). Conclusion Long term activation of TRPV1 with dietary capsaicin significantly blunted AngII-induced contraction response in aortic segments, which was related to the down-regulation of AT1R expression and reduction of AngII-induced calcium entry in VSMCs. Objective We investigated the long-term effect of capsaicin, a transient receptor potential vanilloid 1 (TRPV1) agonist, on vascular reactivity in C57BL/6J mice. Design and methods Two-month-old male C57BL/6J mice were fed with regular diet (control group, n=12) and capsaicin-containing diet (capsaicin group, n=12). Tail-cuff systolic blood pressure (SBP) was examined at the baseline and at the end of the intervention. After 6-month treatment with capsaicin, invasive carotid artery blood pressure and heart rate were measured, and the aortic contraction was examined using isometric myograph (Danish Myotech Technology, Denmark). Plasma levels of renin, angiotensinII (AngII) and aldosterone were determined. Vascular smooth muscle cells (VSMCs) were obtained from thoracic aorta of mice and cultured by tissue explant method. AngiotensinII type 1 receptor (AT1R) protein expression was detected by western blotting. Cytosolic calcium level was detected in VSMCs using the fluorescent dye technique. Results SBP, invasive carotid artery blood pressure and heart rate had no difference between two groups. Norepinephrine-induced contraction response in thoracic aorta was not different; while AngII-induced contraction of aortic ring was lower in the capsaicin group than control group (P<0.05). Plasma levels of renin, AngII and aldosterone were not different between the two groups. Treatment with capsaicin significantly decreased AT1R protein expression and AngII-induced calcium entry in cultured VSMCs (P<0.05). Conclusion Long term activation of TRPV1 with dietary capsaicin significantly blunted AngII-induced contraction response in aortic segments, which was related to the down-regulation of AT1R expression and reduction of AngII-induced calcium entry in VSMCs.

Hemodynamics of dexamethasone-induced hypertension in the rat

Although dexamethasone (DEX) is known to cause hypertension in humans and in animals, the hemodynamic characteristics of DEX-induced hypertension (DEX-HT) in the rat remain unclear. This study evaluated central and regional hemodynamics, and the role of total peripheral resistance (TPR) using a vasodilator minoxidil. Rats were divided into four groups, namely saline (n=20), DEX (n=21), minoxidil+saline (n=10) and minoxidil+DEX (n=10). Tail-cuff systolic blood pressure was recorded every second day. After 10-14 days of treatment, central (saline: n=9, DEX: n=10) and regional (saline: n=11, DEX: n=11) hemodynamic parameters were measured. Central hemodynamic data were also obtained from minoxidil-treated rats. DEX increased blood pressure (P<0.0005) in association with an increase in TPR (P<0.05). However, individual assessments of renal, mesenteric and hindquarter circulations did not detect any significant increase in resistance in these beds. Minoxidil increased cardiac output (P'<0.01) and cardiac index (P'<0.005) as well as decreased TPR (P'<0.05) without affecting DEX-HT. DEX prevented weight gain and decreased thymus weight. The increase in TPR in DEX-HT in rats was not simply explained by isolated alterations to resistance in the renal, mesenteric or hindquarter circulations. Minoxidil effectively prevented the increase in TPR but not the increase in blood pressure, suggesting that an increase in TPR is not essential for DEX-induced blood pressure increase.

Unravelling perinatal programming of the kidney

to the editor: I read with great interest the paper of Baserga et al. ([1][1]), which describes the effect of uterine artery ligation in the pregnant rat on fetal cyclooxygenase-2 (COX-2) expression and blood pressure. This is an important subject and the study presents interesting results, but I