Abstract 357: Role of Blood Pressure in Aldosterone-Mediated Cardiac Injury

Excess aldosterone (ALDO) causes hypertension (HTN), and cardiac hypertrophy, injury and dysfunction. The role of HTN in ALDO-mediated cardiac injury remains controversial. Whether cardiac injury is blood pressure (BP)-dependent, -independent or exacerbated by HTN is not fully understood. We aim to study the role of BP in ALDO-mediated cardiac hypertrophy, inflammation and fibrosis.

Eight-week old uninephrectomized male Sprague Dawley rats (N=6/grp) were randomly assigned to the following 3 groups: Control, ALDO/SALT, ALDO/SALT+3-AHT (Triple Anti-Hypertensive Therapy). ALDO (0.75 μg/h) or vehicle (PEG 300) was administered by osmotic minipumps. SALT (1.0 % NaCl + 0.3 % KCl) was administered in tap water. 3-AHT (240 mg/kg hydralazine, 75 mg/kg hydrochlorothiazide, 15 mg/kg reserpine) was administered in the food. Another set of animals (N=6/grp) was implanted with radiotelemetry probes for BP monitoring. Left ventricle (LV) gene expression (GE) was quantified by qRT-PCR.

3-AHT reduced MAP (126 ± 4 vs. 178 ± 3 mm Hg, p<0.05 vs. ALDO, controls: 108 ± 1). 3-AHT attenuated cardiac (3.8 ± 0.1 vs. 4.0 ± 0.1 HW/BW, p<0.05 vs. ALDO; controls: 3.5 ± 0.1) and LV (2.8 ± 0.1 vs. 3.0 ± 0.1 LVW/BW, p<0.05 vs. ALDO; controls: 2.4 ± 0.1) hypertrophy. 3-AHT abolished ALDO-mediated LV GE upregulation of fibrosis (collagen I, collagen III, fibronectin, Timp1, periostin) and inflammation (osteopontin, MCP-1, TGFβ, Hmox1) markers. A similar effect was observed with novel LV ALDO-target genes such as Reg3b, collagen VIII, Prss35, Ltbp2 or Pcp4. 3-AHT drug administration in the food caused no change in NaCl intake. However, to avoid the confounding effect of the natriuretic drug hydrochlorothiazide, a group of animals was treated with hydralazine and reserpine alone (2-AHT). 2-AHT treatment attenuated HTN (135 ± 4 vs. 178 ± 3 mm Hg, p<0.05 vs. ALDO) but did not modify ALDO-mediated cardiac or LV hypertrophy. However, 2-AHT also abolished ALDO-mediated GE upregulation of fibrosis and inflammation markers, as well as novel LV ALDO-target genes.

These results suggest that ALDO-mediated LV GE regulation in vivo is BP-dependent without excluding that ALDO may exacerbate the HTN-mediated cardiac injury. A stricter BP management may benefit patients with elevated ALDO levels.

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.

Testosterone supplementation in male obese Zucker rats reduces body weight and improves insulin sensitivity but increases blood pressure

Androgen levels are lower in obese men as compared with normal weight individuals. However, there are no safety data regarding the chronic use of androgen supplements in middle-aged men. The present study was undertaken to determine the cardiovascular and metabolic effects of chronic (10 weeks) testosterone treatment in male obese Zucker rats, starting at 22 weeks of age, when testosterone levels were significantly decreased. Testosterone supplements increased plasma levels, 10-fold in both obese Zucker rats and lean Zucker rats. In obese Zucker rats, testosterone supplements reduced body weight, plasma insulin, and cholesterol levels and improved the oral glucose tolerance test. None of these parameters were affected in lean Zucker rats. Mean arterial pressure was significantly increased in obese Zucker rats but not lean Zucker rats. Testosterone supplements increased proteinuria and accelerated renal injury in lean Zucker rats only. Thus, treatment of obese men with chronic testosterone supplements should be done with careful monitoring of blood pressure.

A single pill to treat postmenopausal hypertension? Not yet

Postmenopausal women make up one of the fastest growing populations in the United States. Women typically have a higher incidence of cardiovascular disease following menopause. One of the major risk factors for cardiovascular disease is hypertension, and after menopause, blood pressure (BP) increases progressively in women. Also after menopause, the progression of renal disease increases in women compared with aged matched men. However, the mechanism(s) responsible for the post-menopausal increase in BP and renal injury are yet to be elucidated. Moreover the best therapeutic options to treat postmenopausal hypertension in women are not clear. Hypertension in postmenopausal women are usually associated with other cardiovascular risk factors, such as dyslipidemias, visceral obesity and endothelial dysfunction. Recently it became apparent that in a large number of hypertensive postmenopausal women, their BP is not well controlled with conventional antihypertensive medications. A clear understanding of the complex pathogenesis of postmenopausal hypertension is needed in order to offer the best therapeutic options for these 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 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.

Rosiglitazone reduces blood pressure in female Dahl salt-sensitive rats

Postmenopausal women (PMW) are at greater risk for salt-sensitive hypertension and insulin resistance than premenopausal women. Peroxisome-proliferator-activated receptor-gamma (PPARgamma) agonists reduce blood pressure (BP) and insulin resistance in humans. As in PMW, ovariectomy (OVX) increases salt sensitivity of BP and body weight in Dahl salt-sensitive (DS) rats. This study addressed whether rosiglitazone (ROSI), a PPARgamma agonist, attenuates salt-sensitive hypertension in intact (INT) and OVX DS rats, and if so, whether insulin resistance, nitric oxide (NO), oxidative stress, and/or renal inflammation were contributing mediators. Telemetric BP was similar in OVX and INT on low salt diet (0.3% NaCl), but was higher in OVX than INT on high salt (8% NaCl). ROSI reduced BP in OVX and INT on both low and high salt diet, but only attenuated salt sensitivity of BP in OVX. Nitrate/nitrite excretion (NO(x); index of NO) was similar in INT and OVX on low salt diet, and ROSI increased NO(x) in both groups. High salt diet increased NO(x) in all groups but ROSI only increased NO(x) in OVX rats. OVX females exhibited insulin resistance, increases in body weight, plasma leptin, cholesterol, numbers of renal cortical macrophages, and renal MCP-1 and osteopontin mRNA expression compared to INT. ROSI reduced cholesterol and macrophage infiltration in OVX, but not INT. In summary, PPARgamma activation reduces BP in INT and OVX females, but attenuates the salt sensitivity of BP in OVX only, likely due to increases in NO and in part to reductions in renal resident macrophages and inflammation.

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.

Dihydrotestosterone stimulates aldosterone secretion by H295R human adrenocortical cells

Men exhibit a higher incidence of cardiovascular diseases than do women. The cardiovascular actions of sex steroids have been suggested as primary factors in mediating this sex difference. The mechanisms by which sex steroids, androgens and estrogens, mediate cardiovascular actions remain unclear. Excess aldosterone secretion has been associated with cardiovascular diseases. The hypothesis tested in this study was that at physiological concentrations, androgens stimulate and estradiol inhibits aldosterone secretion by human adrenal cells. In contrast to our hypothesis, physiological concentrations of sex steroids did not modify aldosterone secretion by H295R human adrenocortical cells. However, supraphysiological concentrations (300-1000 nM) of dihydrotestosterone (DHT) significantly stimulated basal and Angiotensin II-mediated aldosterone secretion. The stimulatory effect of DHT on aldosterone secretion was not blocked by the classical androgen receptor blocker flutamide. The stimulatory effect of DHT on aldosterone secretion was also independent of the intra-adrenal renin-angiotensin system since it was neither modified by treatment with the Angiotensin II receptor type 1 blocker losartan or the angiotensin converting enzyme inhibitor captopril. Inhibitors of the calmodulin/calmodulin-dependent protein kinase (CaMK) and protein kinase C intracellular signaling pathways abolished the DHT stimulatory effect on aldosterone secretion by H295R cells. In conclusion, physiological concentrations of sex steroids did not modify aldosterone secretion by human adrenal cells. However, supraphysiological concentrations of DHT-stimulated aldosterone secretion by human adrenal cells by the calmodulin/CaMK and protein kinase C intracellular signaling pathways but independently of the classical androgen receptor. Supraphysiological doses of androgen may promote cardiovascular diseases via stimulation of aldosterone secretion.

Testosterone-dependent hypertension and upregulation of intrarenal angiotensinogen in Dahl salt-sensitive rats

Blood pressure (BP) is more salt sensitive in men than in premenopausal women. In Dahl salt-sensitive rats (DS), high-salt (HS) diet increases BP more in males than females. In contrast to the systemic renin-angiotensin system, which is suppressed in response to HS in male DS, intrarenal angiotensinogen expression is increased, and intrarenal levels of ANG II are not suppressed. In this study, the hypothesis was tested that there is a sexual dimorphism in HS-induced upregulation of intrarenal angiotensinogen mediated by testosterone that also causes increases in BP and renal injury. On a low-salt (LS) diet, male DS had higher levels of intrarenal angiotensinogen mRNA than females. HS diet for 4 wk increased renal cortical angiotensinogen mRNA and protein only in male DS, which was prevented by castration. Ovariectomy of female DS had no effect on intrarenal angiotensinogen expression on either diet. Radiotelemetric BP was similar between males and castrated rats on LS diet. HS diet for 4 wk caused a progressive increase in BP, protein and albumin excretion, and glomerular sclerosis in male DS rats, which were attenuated by castration. Testosterone replacement in castrated DS rats increased BP, renal injury, and upregulation of renal angiotensinogen associated with HS diet. Testosterone contributes to the development of hypertension and renal injury in male DS rats on HS diet possibly through upregulation of the intrarenal renin-angiotensin system.

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.

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-PGF2alpha (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 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.

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.

Disabled-2 is expressed in adrenal zona glomerulosa and is involved in aldosterone secretion

The differentiation of the adrenal cortex into functionally specific zones is probably due to differential temporal gene expression during fetal growth, development, and adulthood. In our search for adrenal zona glomerulosa-specific genes, we found that Disabled-2 (Dab2) is expressed in the zona glomerulosa of the rat adrenal gland using a combination of laser capture microdissection, mRNA amplification, cDNA microarray hybridization, and real-time RT-PCR. Dab2 is an alternative spliced mitogen-regulated phosphoprotein with features of an adaptor protein and functions in signal transduction, endocytosis, and tissue morphogenesis during embryonic development. We performed further studies to analyze adrenal Dab2 localization, regulation, and role in aldosterone secretion. We found that Dab2 is expressed in the zona glomerulosa and zona intermedia of the rat adrenal cortex. Low-salt diet treatment increased Dab2-long isoform expression at the mRNA and protein level in the rat adrenal gland, whereas high-salt diet treatment did not cause any significant modification. Angiotensin II infusion caused a transient increase in both Dab2 isoform mRNAs in the rat adrenal gland. Dab2 overexpression in H295R human adrenocortical cells caused an increase in aldosterone synthase expression and up-regulated aldosterone secretion under angiotensin II-stimulated conditions. In conclusion, Dab2 is an adrenal gland zona glomerulosa- and intermedia-expressed gene that is regulated by aldosterone secretagogues such as low-salt diet or angiotensin II and is involved in aldosterone synthase expression and aldosterone secretion. Dab2 may therefore be a modulator of aldosterone secretion and be involved in mineralocorticoid secretion abnormalities.

Induction of 5-aminolevulinate synthase by activators of steroid biosynthesis

Different cytochromes P450 are involved in steroid biosynthesis. These cytochromes have heme as the prosthetic group. We previously reported that ACTH, an activator of glucocorticoid biosynthesis in adrenal, requires heme biosynthesis for a maximal response. In the present study, we investigated the effect of ACTH, and the effect of two activators of the adrenal mineralocorticoid synthesis, endothelin-1 and low sodium diet on 5-aminolevulinate-synthase (ALA-s) mRNA. ALA-s is the rate-limiting enzyme in heme biosynthesis. It was found that infusion of rats with ACTH for 1 h caused an increase of adrenal ALA-s mRNA and activity accompanied by an increase in plasma corticosterone. CYP21, a cytochrome involved in the synthesis of both corticosterone and aldosterone, was not modified at the RNA level in adrenal glands by 1 h of ACTH infusion. Consistently, infusion of endothelin-1 for 1 h increased ALA-s mRNA and aldosterone content in adrenal gland without modifying CYP21 mRNA levels. To study if ALA-s is also regulated by the main physiological stimuli that increase adrenal mineralocorticoid secretion, we fed rats with low salt diet for 2 or 15 days. Low salt diet treatment increased adrenal gland ALA-s mRNA levels. On the other hand, the rapid stimulation of ALA-s mRNA by ACTH which acts through cyclic AMP was confirmed in H295R human adrenocortical cells, the only human adrenal cell line that has a steroid secretion pattern and regulation similar to primary cultures of adrenal cells. Our findings suggest that the acute activation of adrenal steroidogenic cytochromes by trophic hormones involves an increase in heme biosynthesis which will favor the production of active cytochromes.

Adrenal transcription regulatory genes modulated by angiotensin II and their role in steroidogenesis

Transcription regulatory genes are crucial modulators of cell physiology and metabolism whose intracellular levels are tightly controlled to respond to extracellular stimuli. We studied transcription regulatory genes modulated by angiotensin II, one of the most important regulators of adrenal cortical cell function, and their role in adrenal steroidogenesis in H295R human adrenocortical cells. Angiotensin II-modulated transcription regulatory genes were identified with high-density oligonucleotide microarrays and the results validated by real-time RT-PCR. Cotransfection reporter assays were performed in H295R cells to analyze the role of these transcription regulatory genes in the control of the expression of 11beta-hydroxylase and aldosterone synthase, the last and unique enzymes of the glucocorticoid and mineralocorticoid biosynthetic pathways, respectively. We selected a subset of the most regulated genes for reporter plasmid studies to determine the effect on these enzymes. BHLHB2, BTG2, and SALL1 decreased expression of both enzymes, whereas CITED2, EGR2, ELL2, FOS, FOSB, HDAC5, MAFF, MITF, NFIL3, NR4A1, NR4A2, NR4A3, PER1, and VDR increased expression for both enzymes. By the ratio of aldosterone synthase to 11beta-hydroxylase expression, NFIL3, NR4A1, NR4A2, and NR4A3 show the greatest selectivity toward upregulating expression of the mineralocorticoid biosynthetic pathway preferentially. In summary, this study reports for the first time a set of transcription regulatory genes that are modulated by angiotensin II and their role in adrenal gland steroidogenesis. Abnormal regulation of the mineralocorticoid or glucocorticoid biosynthesis pathways is involved in several pathophysiological conditions; hence the modulated transcription regulatory genes described may correlate with adrenal steroidogenesis pathologies.

HO-1 induction lowers blood pressure and superoxide production in the renal medulla of angiotensin II hypertensive mice

Heme oxygenase-1 (HO-1) induction can attenuate the development of angiotensin II (ANG II)-dependent hypertension. However, the mechanism by which HO-1 lowers blood pressure in this model is not clear. The goal of this study was to test the hypothesis that induction of HO-1 in the kidney can attenuate the increase in reactive oxygen species (ROS) generation in the kidney that occurs during ANG II-dependent hypertension. Mice were divided into four groups, control (Con), cobalt protoporphyrin (CoPP), ANG II, and ANG II + CoPP. CoPP treatment (50 mg/kg) was administered in a single subcutaneous injection 2 days prior to implantation of an osmotic minipump that infused ANG II at a rate of 1 microg x kg(-1) x min(-1). At the end of this period, mean arterial blood pressure (MAP) averaged 93 +/- 5, 90 +/- 5, 146 +/- 8, and 105 +/- 6 mmHg in Con, CoPP-, ANG II-, and ANG II + CoPP-treated mice. To determine whether HO-1 induction resulted in a decrease in ANG II-stimulated ROS generation in the renal medulla, superoxide production was measured. Medullary superoxide production was increased by ANG II infusion and normalized in mice pretreated with CoPP. The reduction in ANG II-mediated superoxide production in the medulla with CoPP was associated with a decrease in extracellular superoxide dismutase protein but an increase in catalase protein and activity. These results suggest that reduction in superoxide and possibly hydrogen peroxide production in the renal medulla may be a potential mechanism by which induction of HO-1 with CoPP lowers blood pressure in ANG-II dependent hypertension.

Angiotensin II-mediated protein kinase D activation stimulates aldosterone and cortisol secretion in H295R human adrenocortical cells

Protein kinases are important mediators in intracellular signaling. Angiotensin II is the most important modulator of adrenal zona glomerulosa cell physiology. Angiotensin II regulates steroidogenesis and proliferation among many other metabolic processes. H295R human adrenal cells are a widely used experimental model to study adrenal cell physiology and metabolism. We screened for protein kinase expression levels using the Kinetwork system in H295R cells after 3 h angiotensin II treatment. Protein kinase D (PKD) was the protein kinase that suffers the most dramatic changes. PKD is a member of a new class of serine/threonine protein kinases that is activated by phosphorylation. Our studies indicated that angiotensin II time- and dose-dependently increased PKD phosphorylation, which occurred within 2 min of angiotensin II treatment and at concentrations as low as 1 nm. PKD phosphorylation was also dose-dependently increased by the PKC activator phorbol 12-myristate 13-acetate. Angiotensin II-mediated PKD phosphorylation was blocked by several PKC inhibitors. Furthermore, PKCepsilon translocation inhibitor peptide decreased angiotensin II-mediated PKD phosphorylation, and PKCepsilon down-regulation by RNA interference also decreased PKD phosphorylation mediated by angiotensin II. Cotransfection of constitutively active PKD mutant constructs up-regulated aldosterone synthase and 11beta-hydroxylase expression in reporter assays. Constitutively active PKD mutants increased aldosterone and cortisol secretion under angiotensin II stimulatory conditions. This study reveals that PKD is an intracellular signaling mediator of angiotensin II regulation of steroidogenesis in human adrenal cells. These data provide new insights into the molecular mechanisms involved in angiotensin II-induced physiological and pathophysiological events in adrenal cells.

Testosterone contributes to marked elevations in mean arterial pressure in adult male intrauterine growth restricted offspring

Our laboratory uses a model of intrauterine growth restriction (IUGR) induced by placental insufficiency in the rat to examine the developmental origins of adult disease. In this model only male IUGR offspring remain hypertensive in adulthood, revealing sex-specific differences. The purpose of this study was to determine whether testosterone with participation of the renin-angiotensin system (RAS) contributes to hypertension in adult male IUGR offspring. At 16 wk of age a significant increase in testosterone (346 +/- 34 vs. 189 +/- 12 ng/dl, P < 0.05) was associated with a significant increase in mean arterial pressure (MAP) measured by telemetry in IUGR offspring (147 +/- 1 vs. 125 +/- 1 mmHg, P < 0.05, IUGR vs. control, respectively). Gonadectomy (CTX) at 10 wk of age significantly reduced MAP by 16 wk of age in IUGR offspring (124 +/- 2 mmHg, P < 0.05 vs. intact IUGR) but had no effect in control (125 +/- 2 mmHg). A significant decrease in MAP in intact IUGR (111 +/- 3 mmHg, P < 0.05 vs. untreated intact IUGR) and castrated IUGR (110 +/- 4 mmHg, P < 0.05 vs. untreated CTX IUGR) after treatment with enalapril for 2 wk suggests a role for RAS involvement. However, the decrease in blood pressure in response to enalapril was greater in intact IUGR (Delta36 +/- 1 mmHg, P < 0.05) compared with CTX IUGR (Delta15 +/- 2 mmHg), indicating an enhanced response to RAS blockade in the presence of testosterone. Thus these results suggest that testosterone plays a role in modulating hypertension in adult male IUGR offspring with participation of the RAS.

RGS2 is regulated by angiotensin II and functions as a negative feedback of aldosterone production in H295R human adrenocortical cells

Regulator 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-ligand interaction. Angiotensin (Ang) II interacts with its G protein-coupled receptor in zona glomerulosa adrenal cells and triggers a cascade of intracellular signals that regulates steroidogenesis and proliferation. We studied Ang II-mediated regulation of RGS2, the role of RGS2 in steroidogenesis, and the intracellular signal events involved in H295R human adrenal cells. We report that both H295R cells and human adrenal gland express RGS2 mRNA. In H295R cells, Ang II caused a rapid and transient increase in RGS2 mRNA levels quantified by real-time RT-PCR. Ang II effects were mimicked by calcium ionophore A23187 and blocked by calcium channel blocker nifedipine. Ang II effects also were blocked by calmodulin antagonists (W-7 and calmidazolium) and calcium/calmodulin-dependent kinase antagonist KN-93. RGS2 overexpression by retroviral infection in H295R cells caused a decrease in Ang II-stimulated aldosterone secretion but did not modify cortisol secretion. In reporter assays, RGS2 decreased Ang II-mediated aldosterone synthase up-regulation. These results suggest that Ang II up-regulates RGS2 mRNA by the calcium/calmodulin-dependent kinase pathway in H295R cells. RGS2 overexpression specifically decreases aldosterone secretion through a decrease in Ang II-mediated aldosterone synthase-induced expression. In conclusion, RGS2 expression is induced by Ang II to terminate the intracellular signaling cascade generated by Ang II. RGS2 alterations in expression levels or functionality could be implicated in deregulations of Ang II signaling and abnormal aldosterone secretion by the adrenal gland.

Impact of androgen-induced oxidative stress on hypertension in male SHR

Men have higher blood pressure than women, and androgens and oxidative stress have been implicated as playing roles in this sexual dimorphism. The spontaneously hypertensive rat (SHR) is an animal model of both androgen- and oxidative stress-mediated hypertension. Therefore, the present studies were performed to test the hypothesis that androgens cause hypertension in SHR in part by stimulating superoxide production via NADPH oxidase. Castration of male SHR reduced blood pressure by 15% and attenuated both basal and NADPH-stimulated superoxide production in kidney cortical homogenates. Expression of p47(phox) and gp91(phox) but not p22(phox) subunits of NADPH oxidase were significantly lower in kidney cortex from castrated males compared with intact males. Moreover, inhibition of NADPH oxidase with apocynin caused approximately 15 mmHg reduction in blood pressure and reduced basal and NADPH-stimulated superoxide production in intact male SHR, but had no effect on blood pressure or superoxide production in castrated males. These data support the hypothesis that androgens cause oxidative stress and thereby increase blood pressure in male SHR via an NADPH oxidase-dependent mechanism.

Sexual dimorphism in the renin-angiotensin system in aging spontaneously hypertensive rats

In young adult spontaneously hypertensive rats (SHR), mean arterial pressure (MAP) is higher in males than in females and inhibition of the renin-angiotensin system (RAS) eliminates this sex difference. After cessation of estrous cycling in female SHR, MAP is similar to that in male SHR. The purpose of this study was to determine the role of the RAS in maintenance of hypertension in aging male and female SHR. At 16 mo of age, MAP was similar in male and female SHR (183+/-5 vs. 193+/-8 mmHg), and chronic losartan (40 mg.kg-1.day-1 po for 3 wk) reduced MAP by 52% (to 90+/-8 mmHg, P<0.05 vs. control) in males and 37% (to 123+/-11 mmHg, P<0.05 vs. control) in females (P<0.05, females vs. males). The effect of losartan on angiotensin type 1 (AT1) receptor blockade was similar: MAP responses to acute doses of ANG II (62.5-250 ng/kg) were blocked to a similar extent in losartan-treated males and females. F2-isoprostane excretion was reduced with losartan more in males than in females. There were no sex differences in plasma renin activity, plasma angiotensinogen or ANG II, or renal expression of AT1 receptors, angiotensin-converting enzyme, or renin. However, renal angiotensinogen mRNA and protein expression was higher in old males than females, whereas renal ANG II was higher in old females than males. The data show that, in aging SHR, when blood pressures are similar, there remains a sexual dimorphism in the response to AT1 receptor antagonism, and the differences may involve sex differences in mechanisms responsible for oxidative stress with aging.

Interleukin-8 synthesis, regulation, and steroidogenic role in H295R human adrenocortical cells

The adrenal gland secretes several cytokines, and cytokines modulate steroid secretion by this gland. In this study, a survey of cytokine production by H295R human adrenocortical cells demonstrated that these cells secreted IL-2, IL-4, IL-8, IL-10, IL-13, and TNFalpha but not IL-5, IL-12, or interferon-gamma. IL-8 was the IL secreted at higher concentration. IL-8 secretion, its regulation, and role in steroidogenesis were further studied. Secreted ILs and steroids were measured by ELISA in cell culture supernatant. IL-8 mRNA was quantified by real-time RT-PCR. H295R cells and human adrenal gland expressed IL-8 mRNA. Angiotensin II, potassium, endothelin-1, IL-1alpha, IL-1beta, TNFalpha, and Escherichia coli lipopolysaccharide dose-dependently increase IL-8 secretion by H295R cells after 24 h incubation. IL-6 had no effect on IL-8 secretion. Angiotensin II time-dependently increased IL-8 secretion by H295R cells up to 48 h. Angiotensin II caused a biphasic increase in IL-8 mRNA expression with a peak 6 h after stimulation. TNFalpha synergized angiotensin II, potassium, and IL-1alpha-mediated IL-8 secretion. IL-8 did not modify aldosterone or cortisol secretion by H295R cells under basal or stimulated (angiotensin II or potassium) conditions. In conclusion, it is demonstrated for the first time that human adrenal cells expressed and secreted IL-8 under the regulation of angiotensin II, potassium, endothelin-1, and immune peptides. Adrenal-secreted IL-8 is one point of convergence between the adrenal gland and the immune system and may have relevance in physiological and pathophysiological conditions associated with increased levels of aldosterone secretagogues and the immune system.

Testosterone supplementation in aging men and women: possible impact on cardiovascular-renal disease

Treatment of aging men and women with testosterone supplements is increasing. The supplements are given to postmenopausal women mainly to improve their libido and to aging men to improve muscle mass and bone strength, to improve libido and quality of life, to prevent and treat osteoporosis, and, with the phosphodiesterase-5 inhibitors, such as sildenafil, to treat erectile dysfunction. The increased use of testosterone supplements in aging individuals has occurred despite the fact that there have been no rigorous clinical trials examining the effects of chronic testosterone on the cardiovascular-renal disease risk. Studies in humans and animals have suggested that androgens can increase blood pressure and compromise renal function. Androgens have been shown to increase tubular sodium and water reabsorption and activate various vasoconstrictor systems in the kidney, such as the renin-angiotensin system and endothelin. There is also evidence that androgens may increase oxidative stress. Furthermore, the kidney contains the enzymes necessary to produce androgens de novo. This review presents an overview of the data from human and animal studies in which the role of androgens in promoting renal and cardiovascular diseases has been investigated.

Role of the renal nerves in blood pressure in male and female SHR

Female spontaneously hypertensive rats (SHR) have lower blood pressures than males. The renin-angiotensin system plays an important role in the sexual dimorphism of blood pressure in SHR. The sympathetic nervous system can stimulate renin release, and, therefore, the present study was performed to determine whether the renal sympathetic nerves play a role in the sexual dimorphism of blood pressure in SHR. Male and female SHR underwent bilateral kidney denervation or sham surgery, and, 2 wk later, mean arterial pressure (MAP) and pulse interval were recorded, and baroreflex sensitivity (BRS) was measured by the sequence technique. Left ventricle index (LVI) was also calculated. MAP was higher in sham-operated males than females (182 +/- 5 vs. 169 +/- 4 mmHg; P < 0.01), but, despite the higher MAP in males, LVI was significantly greater in female rats. BRS was not different between sham-operated male and female SHR. Following bilateral renal denervation, MAP was decreased by a similar percentage (8-10%) in males (169 +/- 2 mmHg) and females (152 +/- 3 mmHg), whereas LVI was reduced only in female SHR. BRS was not altered by renal denervation in either sex. These data indicate that renal nerves play a role in the control of blood pressure in SHR independent of sex, but do not play a role in mediating the sex differences in blood pressure.

Role of endothelin in mediating postmenopausal hypertension in a rat model

Cardiovascular disease is the leading cause of death in women after menopause. Hypertension, a major cardiovascular risk factor, becomes more prevalent after menopause. The mechanisms responsible for the increase in blood pressure (BP) in postmenopausal women are unknown. We have recently characterized the aged, postestrous-cycling (PMR) spontaneously hypertensive rats (SHR) as a model of postmenopausal hypertension. The purpose of the present study was to determine whether endothelin plays a role in the increased BP in PMR. Premenopausal female SHR, aged 4-5 mo (YF), and PMR, aged 16 mo, were studied. Expression of preproendothelin-1 mRNA was not different in either renal cortex or medulla between PMR and YF (n = 7-8/group). In contrast, ET-1 peptide expression was significantly higher in renal cortex of PMR than in renal cortex of YF, but there was no difference in medullary ET-1. Expression of endothelin ET(A) receptor (ET(A)R) mRNA was lower in renal cortex and medulla of PMR than of YF. Additional groups of rats (n = 6-7/group) were treated for 3 wk with the ET(A)R antagonist ABT-627 (5 mg.kg(-1).day(-1)). BP was significantly higher in PMR than in YF. ET(A)R antagonist reduced BP in PMR by 20% to the level found in control YF. ET(A)R antagonist had no effect on BP in YF. These data support the hypothesis that the increase in BP in PMR is mediated in part by endothelin and the ET(A)R.