Licy L. Yanes

Role of Androgens in Mediating Renal Injury in Aging SHR

Abstract—Men have an increased risk of cardiovascular and renal diseases and develop greater renal injury despite similar levels of blood pressure when compared with women. The mechanisms responsible for this predisposition are unknown. Using the spontaneously hypertensive rat (SHR), we have found that androgens play an important role in the development of hypertension in young male SHR. However, the role that androgens play in age-related renal injury and dysfunction in SHR is unknown. Our hypothesis was that despite reductions in serum testosterone with age, androgens mediate renal injury and dysfunction in male SHR. Male SHR were castrated at 8 months of age, studied at 18 months of age, and compared with age-matched, intact males and young intact males (4 months). Serum testosterone was reduced by 30% in aging males compared with young SHR. With castration, blood pressure (mean arterial pressure [MAP]) was decreased by >20 mm Hg compared with old males, glomerular filtration rate (GFR) was increased by >35%, and renal vascular resistance (RVR) was reduced by >40%. MAP, GFR, and RVR in castrated, old males were similar to values in young males. With castration, glomerular sclerosis was reversed and proteinuria was also decreased by >80% when compared with old intact males. In addition, in castrated old males, plasma renin activity was decreased by 30% compared with old males and by 60% compared with young rats. The data support the hypothesis that despite a reduction in testosterone with age, androgens play an important role in age-related renal injury and dysfunction in 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.

Sex Differences in the Pressor Response to Angiotensin II When the Endogenous Renin-Angiotensin System Is Blocked

The present study determined whether there are sex differences in the pressor response to angiotensin II (Ang II) when the endogenous renin-angiotensin system (RAS) is blocked by enalapril (ACEI), and whether this pressor response is changed in the presence of high salt (HS). Telemetry BP was measured in rats treated with ACEI (250 mg/L drinking water) (n=6 to 7/grp), or with ACEI and Ang II (150 ng/kg/min, sc; n=5 to 6/grp), for 3 wk. For the last 2 wk of the study, rats received HS (4% NaCl). MAP was lower in females during baseline (100.8±1.1 versus 105.2±1.3; P<0.05), and with ACEI the last 3 days on normal salt diet (78.8±1.2 versus 88.5±0.9; P<0.05), but increased to higher levels than in males on day 6 of Ang II (129.0±2.2 versus 117.3±2.9; P<0.05). One week of Ang II increased albuminuria in males, but not females, and urinary 8-iso-PGF2&agr; (F2-isoP) was not increased in either males or females. MAP was salt-sensitive in both sexes receiving ACEI, but was only salt-sensitive in males with Ang II (129.3±3.7 versus 145.1±5.7; P<0.05). Albuminuria continued to increase with HS and Ang II in males, but not in females. F2-isoP excretion increased with MAP during the last week of HS and Ang II in males but was independent of MAP in females. With ACEI, MAP in females on normal salt is more responsive to Ang II but is independent of oxidative stress or renal injury. MAP in males is salt-sensitive with Ang II, which may be mediated by oxidative stress and renal injury.

Sex differences in control of blood pressure: role of oxidative stress in hypertension in females.

In general, blood pressure is higher in normotensive men than in age-matched women, and the prevalence of hypertension in men is also higher until after menopause, when the prevalence of hypertension increases for women. It is likely then that the mechanisms by which blood pressure increases in men and women with aging may be different. Although clinical trials to reduce blood pressure with antioxidants have typically not been successful in human cohorts, studies in male rats suggest that oxidative stress plays an important role in mediating hypertension. The exact mechanisms by which oxidative stress increases blood pressure have not been completely elucidated. There may be several reasons for the discrepancies between clinical and animal studies. In this review, the data obtained in selected clinical and animal studies are discussed, and the hypothesis is put forward that oxidative stress may not be as important in mediating hypertension in females as has been shown previously in male rats. Furthermore, it is likely that differences in genetics, age, length of time with hypertension, endothelial dysfunction, and sex are all factored in to modulate the responses to antioxidants in humans. As such, future clinical trials should be designed and powered to evaluate the effects of oxidative stress on blood pressure separately in men and women.

Cardiovascular-renal and metabolic characterization of a rat model of polycystic ovary syndrome

BACKGROUND Polycystic ovary syndrome (PCOS) is the most common reproductive dysfunction in premenopausal women. PCOS is also associated with increased risk of cardiovascular disease when PCOS first occurs and later in life. Hypertension, a common finding in women with PCOS, is a leading risk factor for cardiovascular disease. The mechanisms responsible for hypertension in women with PCOS have not been elucidated. OBJECTIVE This study characterized the cardiovascular-renal consequences of hyperandrogenemia in a female rat model. METHODS Female Sprague-Dawley rats (aged 4-6 weeks) were implanted with dihydrotestosterone or placebo pellets lasting 90 days. After 10 to 12 weeks, blood pressure (by radiotelemetry), renal function (glomerular filtration rate, morphology, protein, and albumin excretion), metabolic parameters (plasma insulin, glucose, leptin, cholesterol, and oral glucose tolerance test), inflammation (plasma tumor necrosis factor-α), oxidative stress (mRNA expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, p22(phox), p47(phox), gp91(phox), and NOX4), nitrate/nitrite excretion and mRNA expression of components of the renin-angiotensin system (angiotensinogen, angiotensin-I-converting enzyme [ACE], and AT1 receptor) were determined. RESULTS Plasma dihydrotestosterone increased 3-fold in hyperandrogenemic female (HAF) rats, whereas plasma estradiol levels did not differ compared with control females. HAF rats exhibited estrus cycle dysfunction. They also had increased food intake and body weight, increased visceral fat, glomerular filtration rate, renal injury, insulin resistance and metabolic dysfunction, oxidative stress, and increased expression of angiotensinogen and ACE and reduced AT1 receptor expression. CONCLUSIONS The HAF rat is a unique model that exhibits many of the characteristics of PCOS in women and is a useful model to study the mechanisms responsible for PCOS-mediated hypertension.

Postmenopausal Hypertension Role of the Renin-Angiotensin System

After menopause, blood pressure increases in women. However, the underlying mechanisms responsible for postmenopausal hypertension are not completely understood. This study was conducted to determine the role that the renin-angiotensin system (RAS) plays in post-menopausal hypertension. Post-estrous cycling (postmenopausal) spontaneously hypertensive rats or young female controls were treated with losartan, an angiotensin (Ang) II type 1 receptor blocker, for 25 days. Mean arterial pressure was recorded continuously by radiotelemetry. Losartan significantly decreased blood pressure in postmenopausal rats and young female controls but failed to normalize blood pressure in postmenopausal rats to levels found in young controls. Plasma renin activity and plasma angiotensinogen were significantly elevated, and intrarenal Ang II type 1 receptor and renin mRNA expression were significantly downregulated in postmenopausal rats. Therefore, RAS only partially contributes to hypertension in postcycling spontaneously hypertensive rats, whereas hypertension in young females is mediated mainly by the RAS. The data suggest that other mechanisms besides activation of the RAS are likely involved in postmenopausal hypertension.

Sex Steroids and Renal Disease: Lessons From Animal Studies

Epidemiological studies have shown that male sex is an independent risk factor for the development and progression of renal disease, and men progress to end stage renal disease (ESRD) faster than premenopausal women in such diseases as autoimmune glomerulonephritis, hypertensive glomerulosclerosis, and polycystic kidney disease.1–3 Although the age-related decline in renal function is also faster in men, women become more susceptible to renal diseases after menopause.4 Insight from in vitro studies and animal models suggest that sex steroids play pivotal roles in modifying the progression to ESRD. Because there is a paucity of data in humans showing the mechanisms by which sex steroids impact renal disease, most of the studies discussed this review will be in animals, mainly rats. Furthermore, determining the roles of sex steroids in various diseases has been done using gonedectomized animals; however, although gonadectomy removes more than sex steroids and most studies only replace the sex steroid of interest, these are still the best studies in which to evaluate mechanisms responsible for sex differences in renal disease. Studies in postmenopausal women will also be kept to a minimum in this review because it is likely that sex steroids change action with aging, as suggested by the Women’s Health Initiative study. Estrogen receptors (ER) are present in the kidney, although their localization in nephron segments has not been fully elucidated. Mesangial cells contain both ERα and ERβ,5 as do endothelium and vascular smooth muscle cells.5–7 Whether the newly described transmembrane estrogen receptor, GPR30,8 is present in kidneys has not been determined. Ovariectomy (ovx) of Dahl salt sensitive rats (DS) caused decreases in ERα but increases in ERβ expression in the renal cortex and medulla,9 whereas ovx in salt resistant (DR) rats caused decreases in cortical and increases in medullary ERα, and …

Postmenopausal hypertension: role of 20-HETE

Blood pressure (BP) increases after menopause. However, the mechanisms responsible have not been elucidated. In this study we tested the hypothesis that 20-hydroxyeicosatetraenoic acids (20-HETE), produced by cytochrome P-450 (CYP450) ω-hydroxylase, contributes to the hypertension in a model of postmenopausal hypertension, aged female spontaneously hypertensive rats (PMR). 1-Aminobenzotriazole, a nonselective inhibitor of arachidonic acid metabolism, for 7 days, reduced BP in PMR but had no effect in young females. Acute intravenous infusion of HET-0016, a specific inhibitor of 20-HETE, over 3 h, also reduced BP in PMR. CYP4A isoform mRNA expression showed no difference in renal CYP4A1 or CYP4A3 but increases in CYP4A2 and decreases in CYP4A8. CYP4A protein expression was decreased in kidney of PMR compared with young females. Endogenous 20-HETE was significantly higher in cerebral vessels of PMR than young females (YF) but was significantly lower in renal vessels of PMR. Omega-hydroxylase activity in cerebral vessels was also higher in PMR but was similar in kidney vessels in both groups. In renal microsomal preparations, endogenous 20-HETE was not different in PMR and young females, but ω-hydroxylase activity was significantly lower in PMR than YF. The data with blockers suggest that 20-HETE contributes to postmenopausal hypertension in SHR. The data also suggest that cerebral production of 20-HETE may be increased and renal tubular production may be decreased in PMR, thus both contributing to their elevated BP.

Regulators of G-protein signaling 4 in adrenal gland: localization, regulation, and role in aldosterone secretion

Regulators of G-protein signaling (RGS proteins) interact with Galpha subunits of heterotrimeric G-proteins, accelerating the rate of GTP hydrolysis and finalizing the intracellular signaling triggered by the G-protein-coupled receptor (GPCR)-ligand interaction. Angiotensin II (Ang II) interacts with its GPCR in adrenal zona glomerulosa cells and triggers a cascade of intracellular signals that regulates steroidogenesis and proliferation. On screening for adrenal zona glomerulosa-specific genes, we found that RGS4 was exclusively localized in the zona glomerulosa of the rat adrenal cortex. We studied RGS4 expression and regulation in the rat adrenal gland, including the signaling pathways involved, as well as the role of RGS4 in steroidogenesis in human adrenocortical H295R cells. We reported that RGS4 mRNA expression in the rat adrenal gland was restricted to the adrenal zonal glomerulosa and upregulated by low-salt diet and Ang II infusion in rat adrenal glands in vivo. In H295R cells, Ang II caused a rapid and transient increase in RGS4 mRNA levels mediated by the calcium/calmodulin/calmodulin-dependent protein kinase and protein kinase C pathways. RGS4 overexpression by retroviral infection in H295R cells decreased Ang II-stimulated aldosterone secretion. In reporter assays, RGS4 decreased Ang II-mediated aldosterone synthase upregulation. In summary, RGS4 is an adrenal gland zona glomerulosa-specific gene that is upregulated by aldosterone secretagogues, in vivo and in vitro, and functions as a negative feedback of Ang II-triggered intracellular signaling. Alterations in RGS4 expression levels or functions may be involved in deregulations of Ang II signaling and abnormal aldosterone secretion.

Roles played by 20-HETE, angiotensin II and endothelin in mediating the hypertension in aging female spontaneously hypertensive rats

Prevalence of hypertension (HT) increases in women after menopause, and there is evidence that HT is not as well controlled in postmenopausal women as men. The reasons for this are not clear but may be related to the lack of adequate blockade of the systems contributing to HT in women. This study aimed to determine the roles of three of the systems known to contribute to HT in animal studies: angiotensin II (ANG II; enalapril inhibitor), eicosanoids [1-aminobenzotriazole (1-ABT) inhibitor], and endothelin (ET(A) receptor antagonist), on blood pressure (BP) in three groups of female spontaneously hypertensive rats (SHR), aged 18 mos (postmenopausal rat, PMR). After baseline telemetry BP, three drug periods were performed for 5 days each: single blockade (ABT or enalapril), double blockade (ABT+enalapril or enalapril+ABT), and triple blockade (all 3 drugs). Controls received no treatment until the third period when they received ET(A) receptor antagonist alone. Single drug blockade reduced BP in PMR to similar levels. Double blockade reduced mean arterial pressure more in ABT+enalapril rats than in the other group (enalapril+ABT). Triple drug blockade reduced BP to similar levels in both groups, but the BP remained ∼110 mmHg. The data suggest that these three systems, ANG II, eicosanoids, and endothelin, contribute together and independently to BP control in old female SHR. However, other systems also contribute to the HT since the BP was not normalized, supporting the notion that HT in postmenopausal women may require complex multidrug therapy to be better controlled and that may require the development of additional drugs.