Blood Pressure In Male Spontaneously Hypertensive Rats Research Articles

Sexual dimorphism in renal heme oxygenase-1 and arachidonic acid metabolizing enzymes in spontaneously hypertensive rats versus normotensive Wistar Kyoto rats

Numerous studies have demonstrated a sexual dimorphism in blood pressure (BP) control in spontaneously hypertensive rats (SHR), however the mechanisms remain to be further elucidated. Based on the established role of arachidonic acid metabolites and heme oxygenase (HO) in BP control, we hypothesize that higher BP in male SHR is associated with differential expression in renal HO and arachidonic acid metabolizing enzymes vs. female SHR. Higher BP in male SHR coincided with significant increases in renal cortical superoxide production and thiobarbituric acid reactive substances (TBARs) levels as measures of oxidative stress compared to normotensive female WKY and female SHR. The elevations in BP and oxidative stress in male SHR were also associated with a decrease in cortical heme oxygenase-1 (HO-1) expression when compared to normotensive female WKY. Although there was no sex or strain differences in cortical expression of the epoxyeicosatrienoic acids (EETs) producing enzyme, cytochrome P450 epoxygenase (CYP2C23), in male and female SHR and WKY, SHR had greater expression of the EETs metabolizing enzyme, soluble epoxide hydrolase (sEH) vs. WKY. Cortical expression of the 20–hydroxyeicosatetraenoic acid (20-HETE) producing enzyme, cytochrome P450 hydroxylase (CYP4A), was less in female WKY and SHR compared to strain-matched males and cortical 20-HETE levels were also less in female SHR vs. male SHR. Cortical cyclooxygenase-2 (COX-2) expression was significantly greater in female SHR and WKY vs. males and cortical prostaglandin E2 (PGE2) levels in female SHR was significantly greater than male WKY. In conclusion, our data suggest that sex differences in renal oxidative stress, HO-1 and arachidonic acid metabolizing enzymes could contribute to sexual dimorphism in hypertension in young SHR.

Inhibition of Necrosis Via Necrox‐5 Attenuates The Development Of Hypertension In Male, But Not Female Spontaneously Hypertensive Rats (SHR)

It is well established that hypertension is accompanied by cell death, however, less is known regarding the role of cell death in blood pressure (BP) control. Necrosis is an uncontrolled pathologic form of cell death that is associated with inflammation. Therefore, the goal of the current study was to test the hypothesis that necrosis contributes to the development of hypertension in SHR. Initial studies measured renal necrosis in 13 wk old male and female SHR (n=9) using flow cytometry. Male SHR had greater renal necrosis compared to female SHR (3.7±0.4% vs. 0.4±0.2% of total renal cells, respectively; p<0.0001). Additional male and female SHR were then randomized to receive vehicle or Necrox‐5 from 6–12 weeks of age (1 mg/kg via IP injection twice weekly; n=4); Necrox‐5 is a cell permeable inhibitor of necrosis that blocks oxidative stress induced necrotic cell death. BP was measured weekly via tail‐cuff analysis and via carotid catheter at sacrifice. Following 6 wks of treatment, kidneys were isolated and necrosis was measured by flow cytometry. Treatment with Necrox‐5 beginning at 6 wks of age attenuated maturation‐induced increases in BP in male SHR (Necrox‐5: 152±11 vs Control: 177±4 mmHg; p=0.07). BP in female SHR was not altered by chronic Necrox‐5 treatment (Necrox‐5: 152±14 vs. Control: 146±11 mmHg; p=0.72). In addition, the sex difference in BP apparent in control rats was abolished by Necrox‐5 treatment. Consistent with these results, Necrox‐5 treatment for 6 wks decreased renal necrosis only in males (Necrox‐5: 1.5±0.5% vs Control: 3±0% of total renal cells). Taken together, our data suggest that greater cell death in male SHR compared to female SHR contributes to sex differences in BP by exacerbating age‐related increases in BP in males.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

IL‐10 Supplementation Decreases BP in Male, But Not Female, Spontaneously Hypertensive Rats

Interleukin 10 (IL‐10) is an anti‐inflammatory cytokine that induces nitric oxide (NO) production. IL‐10 supplementation has previously been shown to lower blood pressure (BP) in male hypertensive mice, but the effect of exogenous IL‐10 in hypertensive females has not yet been studied. For the current study, we hypothesized that chronic infusion of IL‐10 in hypertensive rats would lower BP concomitant with an increase in NO synthase (NOS) activity. First, endogenous basal levels of renal IL‐10+ cells and the IL‐10 receptor were measured in a subset of male and female spontaneously hypertensive rats (SHR). In a second set of rats, baseline BP was recorded by tail cuff plethsmography, and rats were placed in metabolic cages for 24‐hr urine collection prior to initiating infusion of IL‐10. IL‐10 was infused by subcutaneous minipump (3.5 ug/kg/d) in half of the male and female SHR, with the remaining rats serving as sham controls (n=4–6 per treatment group per sex). After 2 weeks of treatment, final BP and metabolic cage timepoints were collected, and tissues were harvested. Female SHR had greater IL‐10+ renal cells than males (flow cytometry, 4.6±0.4 vs 1.9±0.4%, p=0.003, n=8) and greater expression of the IL‐10 receptor (Western blot, 0.4±0.1 vs 0.13±0.1 densitometric units, p=0.03, n=4). BP did not change in female SHR treated with IL‐10 (2‐way ANOVA, p=0.3), but BP significantly decreased following IL‐10 infusion in male rats (p=0.04, Table); BP was higher in males than females in both groups (p<0.001). Urinary protein excretion (Bradford assay) did not differ between treatment and control groups in either sex (Table); but excretion was higher in males than in females (p=<0.001). Contrary to our hypothesis, NOS enzymatic activity (measured by the conversion of radio‐labeled arginine to radio‐labeled citrulline) significantly decreased with IL‐10 treatment in both the inner medulla (p=0.004) and the renal cortex (p=0.003) of both sexes (Table). In conclusion, despite the finding that male SHR have less IL‐10 and IL‐10 receptor expression in the kidney compared to females, BP was selectively decreased in males. We hypothesize that the higher endogenous levels of IL‐10 in the female SHR contribute to the observed sex difference in BP and prevent further decreases in BP with exogenous IL‐10 infusion. Furthermore, our data suggests that decreases in BP in male SHR with IL‐10 is not dependent on upregulating NOS activity in the kidney, although the effect of IL‐10 on NO bioavailability was not assessed. Future studies will further explore the role of endogenous IL‐10 on BP control in female SHR. Baseline BP (mmHg) Final BP (mmHg) Baseline Proteinuria (mg/d) Final Proteinuria (mg/d) Inner Medulla NOS activity (pmol/mg) Cortex NOS activity (pmol/mg) Male CON 211±1 221±5 10±1 15±2 780±123 17287±42772 Male IL‐10 213±5 200±4* 12±1 16±2 284±29* 7316±1917* Female CON 160±8# 169±7# 2±0.4# 3±1# 1296±213# 20260±2207 Female IL‐10 163±2# 169±9# 1±0.3# 2±0# 650±65*# 8279±1215* p<0.05 vs CON same sex, p<0.05 vs male same treatment

Sex Differences in Lamina Terminalis and Hypothalamic Paraventicular Nucleus Activation in Aging Spontaneously Hypertensive Rats (SHR)

Blood pressure in male SHR remains at consistent levels after approximately 9 months of age. In females, however, blood pressure (BP) increases after 10-12 months of age to similar or even higher levels than males. The mechanism(s) for these sex differences are not clear. Although activation of the sympathetic nervous system (SNS) is known to contribute to BP control in both male and female SHR, the role of key brain areas that regulate SNS and cardiovascular activation, e.g. lamina terminalis (LT) and hypothalamic paraventricular nucleus (PVN), are incompletely understood, especially in aged animals. In the present study we tested the hypothesis that there are sex differences in the activation (Fos immunoreactivity, Fos-ir) of the LT and PVN. We also studied estrogen receptor alpha immunoreactivity (ER-α). Fos-ir (p<0.05) was increased in the LT (Organum vasculosum of the LT, subfornical organ (SFO), median preoptic nucleus (MnPO)) in females compared to males. There was also greater activation of the magnocellular hypothalamic neurons (p<0.05), and the parvocellular neurons within the PVN of females compared to males (p<0.005). There was also an increase in the number of ER-α positive cells in the SFO and MnPO (p<0.01), as well as in parvocellular neurons within the PVN (p<0.05) in females compared to males. In contrast to the higher BP in males in young SHR, there was no sex difference in mean arterial pressure (telemetry) at 16 months of age in SHR. These preliminary results suggest a sex difference in activation of brain mechanisms underlying the control of BP in aged animals. Supported by NIH-R01HL66072, PO1HL51971 (JFR), 14POST18640015 (ROM).

Blood Pressure and Mesenteric Vascular Reactivity in Spontaneously Hypertensive Rats 7 Months After Gonadectomy

Sexual dimorphism in the degree of high blood pressure (BP) has been observed in both animal and human hypertension. However, the mechanisms are still poorly understood. We tested the hypothesis that long-term loss of sex steroids promotes changes in mesenteric vascular reactivity that impact the maintenance of hypertension in the spontaneously hypertensive rats (SHR). Male SHR were sham operated (M-SHAM) or castrated (M-CX), and female SHR were sham-operated (F-SHAM) or ovariectomized (F-OVX) at 3 weeks of age. Seven months later, BP was measured in anesthetized rats, and vascular responsiveness was evaluated in the isolated perfused mesentery. Mean arterial BP (mm Hg) was significantly greater in M-SHAM (186 ± 6) compared with F-SHAM (159 ± 5). Gonadectomy reduced BP in male SHR (M-CX: 160 ± 4) but had no significant effect in female SHR (F-OVX: 153 ± 7). Norepinephrine-induced constriction was similar in all groups. Gonadectomy attenuated serotonin-induced vasoconstriction in the mesentery. Acetylcholine (ACh)- and isoproterenol (ISO)-induced vasodilation was greater in female than male SHR. Ovariectomy of female SHR blunted ACh and ISO dilatory responses. ISO dose-response curves were shifted to the left in castrated male SHR. Gonadectomy exerts long-term effects on mesenteric vascular reactivity and hypertension in the SHR.

SEX DIFFERENCES IN OXIDATIVE STRESS AND THE IMPACT ON BLOOD PRESSURE CONTROL AND CARDIOVASCULAR DISEASE

1. In the present review, we addressed studies in humans and rats to determine the role that oxidative stress may play in mediating cardiovascular outcomes. 2. Biochemical evaluation of oxidative stress in both humans and spontaneously hypertensive rats gives equivocal results as to the relative levels in males versus females. Clinical trials with anti-oxidants in humans have not shown consistent results in protecting against detrimental cardiovascular outcomes. In spontaneously hypertensive rats (SHR), blockade studies using tempol or apocynin reduce renal oxidative stress and blood pressure in male SHR, but not in female rats. In addition, increasing oxidative stress with molsidomine increases blood pressure in male, but not female, SHR. Treatment with vitamins E and C reduces blood pressure in young male, but not aged, animals. Furthermore tempol is unable to reduce blood pressure in young male SHR in the absence of a functional nitric oxide system. 3. Neither human nor animal studies are consistent in terms of whether oxidative stress levels are higher in males or females. Furthermore, anti-oxidant therapy in humans often does not ameliorate, or even attenuate, the negative cardiovascular consequences of increased oxidative stress. Our studies in SHR shed light on why these outcomes occur.

Treatment with tetrahydrobiopterin reduces blood pressure in male SHR by reducing testosterone synthesis

Treatment with tetrahydrobiopterin (BH(4)) reduces blood pressure in spontaneously hypertensive rats (SHR). In the present study, we tested the hypothesis that chronic BH(4) reduces blood pressure in male SHR by reducing testosterone biosynthesis mediated by increasing nitric oxide (NO). Male SHR, aged 17-18 wk, intact or castrated, were treated for 1 wk with BH(4) (20 mg.kg(-1).day(-1) ip). After 1 wk, mean arterial pressure (MAP), serum testosterone, and nitrate/nitrite excretion (NO(x)) were measured. MAP was significantly higher in intact males than castrated males (179 +/- 2 vs. 155 +/- 4 mmHg, P < 0.001). In intact males, BH(4) caused a 17% reduction in MAP (148 +/- 2 mmHg), had no effect on NO(x), and reduced serum testosterone by 85% (24.09 +/- 2.37 vs. 3.72 +/- 0.73 ng/dl; P < 0.001). In castrated males, BH(4) had no effect on MAP (152 +/- 5 mmHg) but increased NO(x) by 38%. When castrated males were supplemented with testosterone, MAP increased to the same level as in intact males (180 +/- 7 mmHg), and BH(4) had no effect on MAP (182 +/- 7 mmHg) or NO(x). NO has been shown to decrease testosterone biosynthesis. Chronic sodium nitrite (70 mg.kg(-1).day(-1) x 1 wk) decreased MAP in intact males (150 +/- 4 mmHg) but had no effect on serum testosterone (21.46 +/- 3.08 ng/dl). The data suggest that BH(4) reduces testosterone synthesis and thereby reduces MAP in male SHR, an androgen-dependent model of hypertension. The mechanism(s) by which BH(4) reduces serum testosterone levels are not clear, but the data do not support a role for NO as a mediator.

Sexual dimorphism in the response of thoracic aorta from SHRs to losartan

1. We compared the endothelium-dependent responses of thoracic aortic rings obtained from male and female spontaneously hypertensive rats (SHR) in order to explore gender differences in the normalization of the high blood pressure by antihypertensive drug therapy and in the correction of the endothelial dysfunction found in these animals. 2. Concentration–effect curves to acetylcholine (ACh) and sodium nitroprusside (SNP) were obtained using aortic rings isolated from male and female rats pretreated or not with losartan for 24 h or 15 d. The responses achieved and the EC50s were determined. 3. Losartan, AT 1 receptor antagonist, normalized (around 125 mmHg) the high blood pressure levels in 100% of the females and in 53.3% of males SHR within 24 h of initiating the treatment and remained normal during the remainder of the treatment period (15 d). 4. Losartan (15 d) corrected the decreased response to ACh in male and female SHR, independently of the normalization of blood pressure in male SHR. 5. An increased sensitivity to SNP was observed after chronic treatment with losartan in aortic rings from female SHR. 6. Ridogrel, a TXA 2/PGH 2 receptor antagonist, restored the decreased response to ACh in aortic rings from male and female SHR. 7. These results suggest that there are gender-related differences in the normalization of the high blood pressure levels by losartan in SHR. The decreased response to ACh observed in male and female is corrected after sustained (15 d) reduction of high blood pressure. In female but not in male SHR, correction seems to involve an increased sensitivity of the smooth muscle to nitric oxide.

Attenuation of genetic hypertension after short-term vasopressin V1A receptor antagonism.

Abnormalities of the vasopressin system are found in genetic hypertension. This study compares the delayed effects of a brief period of vasopressin V1A receptor blockade and angiotensin-converting enzyme inhibition in young female and male spontaneously hypertensive rats (SHR) on the development of hypertension in adult life. In a separate study, the role of vasopressin in the maintenance of blood pressure in adult SHR was assessed. Young SHR received either the nonpeptide vasopressin V1A receptor antagonist OPC-21268, the angiotensin-converting enzyme inhibitor ramipril, or vehicle from 6 to 10 weeks of age. During the treatment period, OPC-21268 and ramipril reduced systolic blood pressure compared with control SHR (P < .001). Blood pressure in male SHR 7 weeks after treatment withdrawal was 178 +/- 1 mm Hg in ramipril-treated, 184 +/- 1 mm Hg in OPC-21268-treated, and 200 +/- 2 mm Hg in control SHR (P < .001). Similar results were seen in female SHR, although both OPC-21268 and ramipril were less effective antihypertensive agents in female compared with male SHR. The sustained attenuation in blood pressure was not associated with significant cardiovascular structural changes (left ventricular-to-body weight ratio, renal weight-to-body weight ratio, mesenteric resistance artery media-to-lumen ratio). Results of vasopressin V1A receptor binding kinetics and plasma renin or aldosterone concentrations did not suggest a lasting effect of OPC-21268 on the vasopressin system or of ramipril on the renin-angiotensin system following treatment withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex influence on renal alpha 2-adrenergic receptor density in the spontaneously hypertensive rat.

Male spontaneously hypertensive rats (SHR) have higher blood pressure than females. We compared renal alpha 2-adrenergic receptor density among intact SHR and Wistar-Kyoto (WKY) rats of both sexes, male and female SHR gonadectomized at 4 weeks of age, and gonadectomized SHR supplemented with testosterone. Additional groups of SHR were treated with enalapril (30 mg/kg per day), an angiotensin-converting enzyme inhibitor, from 5 to 14 weeks of age. Renal alpha 2-adrenergic receptor density was higher in males than females in both SHR and WKY rats. Female SHR and WKY rats had identical low renal alpha 2-adrenergic receptor density. Castration of male SHR reduced the male-female differences in blood pressure and renal alpha 2-adrenergic receptor density by 60%. Treatment with testosterone raised blood pressure and renal alpha 2-adrenergic receptor density to the intact male levels in both gonadectomized males and females. Treatment with enalapril decreased blood pressure but not renal alpha 2-adrenergic receptor density in both male and female SHR. We conclude that (1) both renal alpha 2-adrenergic receptor density and blood pressure are influenced by sex in SHR and WKY, (2) renal alpha 2-adrenergic receptor density like blood pressure is regulated by androgens, and (3) increased renal alpha 2-adrenergic receptor density is not a consequence of high blood pressure in male SHR.

Preventive effects of whey mineral concentrate on the development of hypertension in SHR.

Preventive effects of whey mineral concentrate which contained most of the milk minerals and low molecular weight whey protein on the development of hypertension in spontaneously hypertensive rats (SHR) were investigated. SHR after weaning were fed the experimental regimen (whey mineral diet or control diet) and maintained on these diets for approx. 10 weeks. A significant inhibition of development of hypertension was observed in the 4th week with male SHR fed the whey mineral diet compared with sex-matched SHR fed the control diet supplemented with a NaCl equivalent. The decrease in blood pressure became more pronounced as the period proceeded. The average blood pressure in male SHR at the end of the experiment was 213mmHg (whey mineral group) and 236mmHg in the control group. A similar result was obtained with female SHR. Accompanying attenuation of blood pressure, urinary excretion of Na and retention of Ca were enhanced by ingestion of the whey mineral concentrate. Blood pressure correlated inversely with urinary Na excretion (r=-0.62), and positively with urinary Ca excretion (r=0.78). Which factor in whey mineral concentrate mainly contributes to these effects, remains unclarified.