Effect of oral contraceptives on the renin angiotensin system and renal function

We examined the effect of oral contraceptive (OC) usage on the renin angiotensin system (RAS) in two related experiments. In the first experiment, subjects were 34 healthy, normotensive, premenopausal women, 15 OC users and 19 OC nonusers, mean age 25 +/- 1 yr, ingesting a controlled sodium diet. We assessed arterial pressure, glomerular filtration rate, effective renal plasma flow, renal vascular resistance (RVR), and filtration fraction (FF) using inulin and p-aminohippurate clearance techniques, both at baseline and in response to the ANG II receptor blocker losartan. In the second experiment, in similar subjects, 10 OC users and 10 nonusers, we examined circulating RAS components [angiotensinogen, ANG II, aldosterone, plasma renin activity (PRA), and active renin] in response to incremental lower body negative pressure (LBNP), to determine whether renin secretion is suppressed by OC usage. OC users exhibited elevations in systolic blood pressure, RVR, and FF compared with nonusers, which were partially corrected by losartan. In the LBNP phase of the study, baseline measures of PRA, angiotensinogen, ANG II, and aldosterone were all increased in the OC group compared with the control group. Active renin levels did not differ between groups. Incremental LBNP resulted in increased circulating levels of RAS components in both groups. We conclude that the RAS is activated in women using OCs. There was no evidence that decreases in renin secretion result in normalization of the RAS as a whole.     

ACE2 is expressed in mouse adipocytes and regulated by a high-fat diet

Adipose tissue expresses components of the renin-angiotensin system (RAS). Angiotensin converting enzyme (ACE2), a new component of the RAS, catabolizes the vasoconstrictor peptide ANG II to form the vasodilator angiotensin 1-7 [ANG-(1-7)]. We examined whether adipocytes express ACE2 and its regulation by manipulation of the RAS and by high-fat (HF) feeding. ACE2 mRNA expression increased (threefold) during differentiation of 3T3-L1 adipocytes and was not regulated by manipulation of the RAS. Male C57BL/6 mice were fed low- (LF) or high-fat (HF) diets for 1 wk or 4 mo. At 1 wk of HF feeding, adipose expression of angiotensinogen (twofold) and ACE2 (threefold) increased, but systemic angiotensin peptide concentrations and blood pressure were not altered. At 4 mo of HF feeding, adipose mRNA expression of angiotensinogen (twofold) and ACE2 (threefold) continued to be elevated, and liver angiotensinogen expression increased (twofold). However, adipose tissue from HF mice did not exhibit elevated ACE2 protein or activity. Increased expression of ADAM17, a protease responsible for ACE2 shedding, coincided with reductions in ACE2 activity in 3T3-L1 adipocytes, and an ADAM17 inhibitor decreased media ACE2 activity. Moreover, ADAM17 mRNA expression was increased in adipose tissue from 4-mo HF-fed mice, and plasma ACE2 activity increased. However, HF mice exhibited marked increases in plasma angiotensin peptide concentrations (LF: 2,141 +/- 253; HF: 6,829 +/- 1,075 pg/ml) and elevated blood pressure. These results demonstrate that adipocytes express ACE2 that is dysregulated in HF-fed mice with elevated blood pressure compared with LF controls.     

Enhanced intrarenal receptor-mediated prorenin activation in chronic progressive anti-thymocyte serum nephritis rats on high salt intake

Despite suppression of the circulating renin-angiotensin system (RAS), high salt intake (HSI) aggravates kidney injury in chronic kidney disease. To elucidate the effect of HSI on intrarenal RAS, we investigated the levels of intrarenal prorenin, renin, (pro)renin receptor (PRR), receptor-mediated prorenin activation, and ANG II in chronic anti-thymocyte serum (ATS) nephritic rats on HSI. Kidney fibrosis grew more severe in the nephritic rats on HSI than normal salt intake. Despite suppression of plasma renin and ANG II, marked increases in tubular prorenin and renin proteins without concomitant rises in renin mRNA, non-proteolytically activated prorenin, and ANG II were noted in the nephritic rats on HSI. Redistribution of PRR from the cytoplasm to the apical membrane, along with elevated non-proteolytically activated prorenin and ANG II, was observed in the collecting ducts and connecting tubules in the nephritic rats on HSI. Olmesartan decreased cortical prorenin, non-proteolytically activated prorenin and ANG II, and apical membranous PRR in the collecting ducts and connecting tubules, and attenuated the renal lesions. Cell surface trafficking of PRR was enhanced by ANG II and was suppressed by olmesartan in Madin-Darby canine kidney cells. These data suggest the involvement of the ANG II-dependent increase in apical membrane PRR in the augmentation of intrarenal binding of prorenin and renin, followed by nonproteolytic activation of prorenin, enhancement of renin catalytic activity, ANG II generation, and progression of kidney fibrosis in the nephritic rat kidneys on HSI. The origin of the increased tubular prorenin and renin remains to be clarified. Further studies measuring the urinary prorenin and renin are needed.     

Myocardial renin is neither necessary nor sufficient to initiate or maintain ventricular hypertrophy

We tested the hypothesis that the myocardial renin-angiotensin system (RAS) is both necessary and sufficient to initiate and maintain all classes of ventricular hypertrophy. Myocardial and plasma renin and angiotensinogen were measured in rats during initiation and maintenance of ventricular hypertrophy associated with DOCA implants and 1% NaCl drinking water, with and without the AT(1) ANG II receptor blocker losartan. Additional groups of rats were given a low-sodium diet (0.04%) for 3 wk. Ventricular hypertrophy was initiated within 7 days and maintained for 35 days in DOCA-treated rats despite significantly low myocardial and plasma renin, normal or low myocardial and plasma angiotensinogen, or the presence of losartan. Furthermore, there was no ventricular hypertrophy in low-salt diet-fed animals despite increased myocardial and plasma renin levels and normal angiotensinogen levels. Therefore, the myocardial RAS is not necessary to initiate or maintain cardiac hypertrophy in DOCA-treated rats and is not sufficient to initiate cardiac hypertrophy in low-salt diet-fed rats. Additionally, myocardial renin and angiotensinogen were significantly correlated with corresponding plasma levels.     

Activity and responsiveness of the renin-angiotensin system in the aging rat

The systemic renin-angiotensin system (RAS) is suppressed in normal aging, but the activity of the tissue RAS is not well defined. We examined the systemic and intrarenal RAS status of aging normal rats and responses to suppression and stimulation of the production of endogenous ANG II. Studies were performed in young (3 mo) and early aging (15 mo) male Sprague-Dawley rats. Angiotensin-converting enzyme inhibitors modestly decreased mean arterial pressure (MAP) in young (3 mo) and early aging (15 mo) rats and limited proteinuria in the older rats. There were no significant age-related effects on renal function or on endogenous RAS activity. Intravenous infusion of the precursor ANG I led to comparable increases in MAP in younger and older rats. In contrast, the renal effects (reduction in glomerular filtration and plasma flow rates) were exaggerated in the older animals. Intrarenal arterial ANG I did not affect MAP in any group. In young rats, there were no significant hemodynamic effects in either the ipsilateral (infused) or the contralateral (noninfused) kidney. In the older rats, both kidneys had a significant fall in renal renal plasma flow rate (RPF) with left renal arterial infusion of ANG I. Accordingly, these studies early in the course of aging found only subtle changes in the activity, responsiveness, and metabolism of the RAS. Thus early aging is associated with a modest but important increase in sensitivity to RAS stimulation.     

Evolving concepts of the intrarenal renin-angiotensin system in health and disease: contributions of molecular biology.

Previous physiological and biochemical studies suggest the existence of an endogenous renin-angiotensin system (RAS) in the kidney. However, these data cannot exclude the contribution of the circulating RAS. Proof of the local synthesis of RAS components in the kidney has been obtained recently through the use of molecular biological techniques. Using Northern blot analysis, we have demonstrated the intrarenal expression of renin, angiotensinogen, and angiotensin-converting enzyme messenger RNAs. Employing in situ hybridization histochemistry, we have localized the intrarenal tissue sites of renin and angiotensinogen messenger RNA synthesis. Renin gene expression was found in cells of the juxtaglomerular apparatus. Angiotensinogen mRNA was primarily produced in the proximal convoluted tubule with lesser amounts in glomerular tufts and vasculature. These findings led us to hypothesize that the proximal tubule is a major site of renal Ang II synthesis and that locally synthesized Ang II might directly modulate tubular function. Both genes are subject to feedback regulation. Our studies showed that Ang II exerted a stimulatory effect on angiotensinogen but a negative feedback effect on renin gene expression. Dietary NaCl restriction stimulated the expression of both genes, although the onset of renin gene activation required more prolonged sodium chloride restriction. Furthermore, our data indicated that the sodium cation, irrespective of the anion, was primarily important in regulating renal angiotensinogen mRNA levels. Our studies also showed altered intrarenal renin or angiotensinogen expressions in pathophysiological states, e.g. in experimental heart failure and the spontaneously hypertensive rat. Taken together, these data support the existence of a intrarenal RAS and suggest its potential roles in the regulation of renal function in health and disease.     

Local renin-angiotensin systems

The existence of a local cardiovascular renin-angiotensin system (RAS) is often invoked to explain the long-term beneficial effects of RAS inhibitors in heart failure and hypertension. The implicit assumption is that all components of the RAS are synthesized in situ, so that local angiotensin II formation may occur independently of the circulating RAS. Evidence for this assumption however is lacking. The angiotensin release from isolated perfused rat hearts or hindlimbs depends on the presence of renal renin. When calculating the in vivo angiotensin production at tissue sites in humans and pigs, taking into account the extensive regional angiotensin clearance by infusing radiolabeled angiotensin I or II, it was found that angiotensin production correlated closely with plasma renin activity. Moreover, in pigs the cardiac tissue levels of renin and angiotensin were directly correlated with their respective plasma levels, and both in tissue and plasma the levels were undetectably low after nephrectomy. Similarly, rat vascular renin and angiotensin decrease to low or undetectable levels within 48 h after nephrectomy. Aortic renin has a longer half life than plasma renin, suggesting that renin may be bound by the vessel wall. In support of this assumption, both renin receptors and renin-binding proteins have been described. Like ACE, renin was enriched in a purified membrane fraction prepared from cardiac tissue. Binding of renin to cardiac or vascular membranes may therefore be part of a mechanism by which renin is taken up from plasma. It appears that the concept of a local RAS needs to be reassessed. Local angiotensin formation in heart and vessel wall does occur, but depends, at least under normal circumstances, on the uptake of renal renin from the circulation. Tissues may regulate their local angiotensin concentrations by varying the number of renin receptors and/or renin-binding proteins, the ACE level, the amount of metabolizing enzymes and the angiotensin receptor density.Abbreviations RAS renin-angiotensin system - ANG angiotensin - ACE angiotensin-converting enzyme - PRA plasma renin activity     

Immunoreactive renin and angiotensin II in the afferent glomerular arterioles of rats with hypertension due to unilateral renal artery constriction

Summary The immunoreactivity for renin and angiotensin II (ANG II) in the ischaemic and non-ischaemic kidney of rats with renovascular hypertension was compared with that of the kidneys of sham operated controls. In addition, the renin concentration of these kidneys and the plasma level of ANG II were determined in hypertensive and control animals. In parallel with the renin concentration of kidney cortex, the immunoreactivity, i.e. the JG-index for renin of the afferent arterioles from the ischaemic kidney was slighly increased, that from the nonischaemic kidney drastically decreased as compared to control kidneys. Similarly, the JG-index for ANG II was increased in the ischaemic and decreased in the non-ischaemic kidney although the plasma level of ANG II was elevated in the animals with renovascular hypertension. This difference in the immunocytochemically detectable ANG II and especially the decrease of ANG II in the non-ischaemic kidney in spite of elevated plasma ANG II levels is interpreted to result from similar differences in the local (extravascular) formation of ANG II by the intrarenal renin-angiotensin system.These studies were supported by the Deutsche Forschungsgemeinschaft within the SFB 90 Cardiovasculäres System     

Placental insufficiency results in temporal alterations in the renin angiotensin system in male hypertensive growth restricted offspring

Reduced uterine perfusion initiated in late gestation in the rat results in intrauterine growth restriction (IUGR) and development of hypertension by 4 wk of age. We hypothesize that the renin angiotensin system (RAS), a regulatory system important in the long-term control of blood pressure, may be programmed by placental insufficiency and may contribute to the etiology of IUGR hypertension. We previously reported that RAS blockade abolished hypertension in adult IUGR offspring; however, the mechanisms responsible for the early phase of hypertension are unresolved. Therefore, the purpose of this study was to examine RAS involvement in early programmed hypertension and to determine whether temporal changes in RAS expression are observed in IUGR offspring. Renal renin and angiotensinogen mRNA expression were significantly decreased at birth (80 and 60%, respectively); plasma and renal RAS did not differ in conjunction with hypertension (mean increase of 14 mmHg) in young IUGR offspring; however, hypertension (mean increase of 22 mmHg) in adult IUGR offspring was associated with marked increases in renal angiotensin-converting enzyme (ACE) activity (122%) and renal renin and angiotensinogen mRNA (7-fold and 7.4-fold, respectively), but no change in renal ANG II or angiotensin type 1 receptor. ACE inhibition (enalapril, 10 mg x kg(-1) x day(-1), administered from 2 to 4 wk of age) abolished hypertension in IUGR at 4 wk of age (decrease of 15 mmHg, respectively) with no significant depressor effect in control offspring. Therefore, temporal alterations in renal RAS are observed in IUGR offspring and may play a key role in the etiology of IUGR hypertension.     

Dual RAS blockade normalizes angiotensin-converting enzyme-2 expression and prevents hypertension and tubular apoptosis in Akita angiotensinogen-transgenic mice

We investigated the effects of dual renin-angiotensin system (RAS) blockade on angiotensin-converting enzyme-2 (Ace2) expression, hypertension, and renal proximal tubular cell (RPTC) apoptosis in type 1 diabetic Akita angiotensinogen (Agt)-transgenic (Tg) mice that specifically overexpress Agt in their RPTCs. Adult (11 wk old) male Akita and Akita Agt-Tg mice were treated with two RAS blockers (ANG II receptor type 1 blocker losartan, 30 mg·kg(-1)·day(-1)) and angiotensin-converting enzyme (ACE) inhibitor perindopril (4 mg·kg(-1)·day(-1)) in drinking water. Same-age non-Akita littermates and Agt-Tg mice served as controls. Blood pressure, blood glucose, and albuminuria were monitored weekly. The animals were euthanized at age 16 wk. The left kidneys were processed for immunohistochemistry and apoptosis studies. Renal proximal tubules were isolated from the right kidneys to assess gene and protein expression. Urinary ANG II and ANG 1-7 were quantified by ELISA. RAS blockade normalized renal Ace2 expression and urinary ANG 1-7 levels (both of which were low in untreated Akita and Akita Agt-Tg), prevented hypertension, albuminuria, tubulointerstitial fibrosis and tubular apoptosis, and inhibited profibrotic and proapoptotic gene expression in RPTCs of Akita and Akita Agt-Tg mice compared with non-Akita controls. Our results demonstrate the effectiveness of RAS blockade in preventing intrarenal RAS activation, hypertension, and nephropathy progression in diabetes and support the important role of intrarenal Ace2 expression in modulating hypertension and renal injury in diabetes.     

Angiotensin biosynthesis and concentrations in brain of normotensive and hypertensive rats

We report here on the extraction and characterization of angiotensin I (ANG I) and angiotensin II (ANG II) from the brain of rats. High pressure liquid chromatography (HPLC) with different mobile phases combined with specific radioimmunoassays (RIA) proved to be a powerful tool for peptide characterization in biological samples; (Ile5)-ANG I, (Ile5)-ANG II and (Ile5)-ANG III could clearly be identified in cerebrospinal fluid (CSF), incubated in vivo and in vitro with renin, in total brain extracts, as well as in hypothalamus (HT), medulla oblongata (MO), cerebellum (CER) and cortex (CO). Angiotensin cleaved from CSF angiotensinogen and angiotensin extracted from brain showed retention times identical to those of plasma angiotensin and synthetic standard peptides, indicating that their amino acid sequence is probably identical. ANG I and ANG II were highest in the HT and lowest in the CO. Following bilateral nephrectomy (NX) both ANG I and ANG II persisted at control levels. Young 10 week old spontaneously hypertensive rats (SHRSP) showed significantly lower ANG I and ANG II concentrations in the HT compared with Wistar Kyoto rats (WKY). Intracerebroventricular (i.c.v.) administration of the converting enzyme inhibitor captopril caused a significant increase in ANG 1 in nephrectomized SHRSP but not in WKY. These differences were not found in 40 week old SHRSP. The data show that ANG I and ANG II are synthetized in the brain of rats. The lower concentrations and the enhanced accumulation of ANG I after converting enzyme blockade in nephrectomized young SHRSP indicate an increased turnover of angiotensin in hypertensive rats.     

Novel expression and regulation of the renin-angiotensin system in metanephric organ culture

To evaluate the presence and regulation of the renin-angiotensin system (RAS) in metanephric organ culture, embryonic day 14 (E14) rat metanephroi were cultured for 6 days. mRNAs for renin and both ANG II receptors (AT(1) and AT(2)) are expressed at E14, and all three genes continue to be expressed in culture. Renin mRNA is localized to developing tubules and ureteral branches in the cultured explants. At E14, renin immunostaining is found in isolated cells scattered within the mesenchyme. As differentiation progresses, renin localizes to the ureteric epithelium, developing tubules and glomeruli. E14 metanephroi contain ANG II, and peptide production persists in culture. Renin activity is present at E14 (6.13 +/- 0.61 pg ANG I. kidney(-1). h(-1)) and in cultured explants (28.84 +/- 1. 13 pg ANG I. kidney(-1). h(-1)). Renin activity in explants is increased by ANG II treatment (70.1 +/- 6.36 vs. 40.97 +/- 1.94 pg ANG I. kidney(-1). h(-1) in control). This increase is prevented by AT(1) blockade, whereas AT(2) antagonism has no effect. These studies document an operational local RAS and a previously undescribed positive-feedback mechanism for renin generation in avascular, cultured developing metanephroi. This novel expression pattern and regulatory mechanism highlight the unique ability of developing renal cells to express an active RAS.     

Effect of ANG II type I receptor antagonist and ACE inhibitor on vitamin D receptor-null mice

We recently showed that vitamin D receptor (VDR) inactivation results in deregulated stimulation of the renin-angiotensin system (RAS). To address further the relation between RAS activation and the abnormalities in electrolyte and volume homeostasis, we studied the effect of the ANG II type I receptor antagonist losartan and the angiotensin-converting enzyme inhibitor captopril on VDR-null mice. Treatment with losartan or captopril normalized the water intake and urine excretion of VDR-null mice. However, the increase in salt excretion in VDR-null mice was not affected by either drug, suggesting that this abnormality is independent of the RAS. Northern blot and immunohistochemical analyses revealed that both drugs caused a drastic stimulation of renin expression in wild-type and VDR-null mice, but renin expression remained much higher in the treated VDR-null mice than in the treated wild-type mice, suggesting that the ANG II feedback mechanism remains intact in the mutant mice. These data firmly established a causative relation between RAS overstimulation and the abnormal volume homeostasis in VDR-null mice and demonstrated that vitamin D repression of renin expression is independent of the ANG II feedback regulation in vivo.     

The effect of hypothalamo-pituitary disconnection on the renin-angiotensin system in the late-gestation fetal sheep

The activity of the renin-angiotensin system (RAS) increases significantly in the late-gestation fetal sheep. Fetal cortisol is also increased during this time, and it is thought that the increase in cortisol may modulate the RAS changes. Previous studies have examined the effects of cortisol infusion on RAS activity, but the effects of blocking the peripartum increase in cortisol concentrations on the developmental changes in the RAS are not known. Therefore, we utilized the technique of hypothalamic-pituitary disconnection (HPD), which prevents the cortisol surge from occurring, to investigate the importance of the late-gestation increase in cortisol on the ontogenic changes in RAS activity. HPD of fetal sheep was performed at 120 days of gestational age (dGA), and fetuses were delivered between 135 and 139 dGA. Control fetuses were sham operated. HPD blocked the late-gestation cortisol increase but did not alter renal renin mRNA, renal renin or prorenin protein content, nor plasma renin levels compared with sham operated. However, HPD fetuses had increased ANG II receptor subtype 1 (AT1) mRNA and protein expression in the kidney and lungs. ANG II receptor subtype 2 (AT2) expression was not altered in these tissues at either mRNA or protein level. HPD did not change AT1 or AT2 mRNA in the left ventricle but did result in decreased protein levels for both receptors. These studies demonstrate that blockade of the naturally occurring increase in fetal cortisol concentration in late gestation is associated with tissue-specific alterations in expression of AT1 and AT2 receptors. These changes may impact on fetal tissue maturation and hence have consequences in postnatal life.     

Physiological elevation in plasma angiotensinogen increases blood pressure

Hepatic angiotensinogen secretion is controlled by a complex pattern of physiological or pathophysiological mediators. Because plasma concentrations of angiotensinogen are close to the Michaelis-Menten constant, it was hypothesized that changes in circulating angiotensinogen affect the formation rate of ANG I and ANG II and, therefore, blood pressure. To further test this hypothesis, we injected purified rat angiotensinogen intravenously in Sprague-Dawley rats via the femoral vein and measured mean arterial blood pressure after arterial catheterization. In controls, mean arterial pressure was 131 +/- 2 mmHg before and after the injection of vehicle (sterile saline). The injection of 0.8, 1.2, and 2.9 mg/kg angiotensinogen caused a dose-dependent increase in mean arterial blood pressure of 8 +/- 0.4, 19.3 +/- 2.1, and 32 +/- 2.4 mmHg, respectively. In contrast, the injection of a purified rabbit anti-rat angiotensinogen antibody (1.4 mg/kg) resulted in a significant decrease in mean arterial pressure (-33 +/- 3.2 mmHg). Plasma angiotensinogen increased to 769 +/- 32, 953 +/- 42, and 1,289 +/- 79 pmol/ml, respectively, after substrate and decreased by 361 +/- 28 pmol/ml after antibody administration. Alterations in plasma angiotensinogen correlated well with changes in plasma renin activity. In summary, variations in circulating angiotensinogen can result in changes in blood pressure. In contrast to renin, which is known as a tonic regulator for the generation of ANG I, angiotensinogen may be a factor rather important for long-term control of the basal activity of the renin-angiotensin system.     

Receptor-dependent prorenin activation and induction of PAI-1 expression in vascular smooth muscle cells

Although elevated plasma prorenin levels are commonly found in diabetic patients and correlate with microvascular complications, the pathological role of these increases, if any, remains unclear. Prorenin/renin binding to the prorenin/renin receptor [(p)RR] enhances the efficiency of angiotensinogen cleavage by renin and unmasks prorenin catalytic activity. We asked whether plasma prorenin could be activated in local vascular tissue through receptor binding. Immunohistochemical staining showing localization of the (p)RR in the aorta to vascular smooth muscle cells (VSMCs). After cultured rat VSMCs were incubated with 10(-7) M inactive prorenin, cultured supernatant acquired the ability to generate ANG I from angiotensinogen, indicating that prorenin had been activated. Activated prorenin facilitated angiotensin generation in cultured VSMCs when exogenous angiotensinogen was added. Small interfering RNA (siRNA) against the (p)RR blocked this activation and subsequent angiotensin generation. Prorenin alone induced dose- and time-dependent increases in mRNA and protein for the profibrotic molecule plasminogen activator inhibitor (PAI)-1, effects that were blocked by siRNA, but not by the ANG II receptor antagonist saralasin. When inactive prorenin and angiotensinogen were incubated with cells, PAI-1 mRNA increased a striking 54-fold, 8-fold higher than the increase seen with prorenin alone. PAI-1 protein increased 2.75-fold. These effects were blocked by treatment with siRNA + saralasin. We conclude that prorenin at high concentration binds the (p)RR on VSMCs and is activated. This activation leads to increased expression of PAI-1 via ANG II-independent and -dependent mechanisms. These data provide a mechanism by which elevated prorenin levels in diabetes may contribute to the progression of fibrotic disease.     

Divergent mechanism regulating fluid intake and metabolism by the brain renin-angiotensin system

The purpose of this review is two-fold. First, I will highlight recent advances in our understanding of the mechanisms regulating angiotensin II (ANG II) synthesis in the brain, focusing on evidence that renin is expressed in the brain and is expressed in two forms: a secreted form, which may catalyze extracellular ANG I generation from glial or neuronal angiotensinogen (AGT), and an intracellular form, which may generate intracellular ANG in neurons that may act as a neurotransmitter. Second, I will discuss recent studies that advance the concept that the renin-angiotensin system (RAS) in the brain not only is a potent regulator of blood pressure and fluid intake but may also regulate metabolism. The efferent pathways regulating the blood pressure/dipsogenic effects and the metabolic effects of elevated central RAS activity appear different, with the former being dependent upon the hypothalamic-pituitary-adrenal axis, and the latter being dependent upon an interaction between the brain and the systemic (or adipose) RAS.     

Thyroid hormone modulates renin and ANG II receptor expression in fetal sheep

Fetal renin-angiotensin system (RAS) activity is developmentally regulated, increasing in late gestation toward term. At the same time, fetal hemodynamic parameters change, with blood pressure increasing and heart rate decreasing. During this period, fetal plasma thyroid hormone concentrations also increase significantly. In this study we utilized the technique of thyroidectomy (TX), which removes thyroid hormone from the circulation, to investigate the importance of thyroid hormone on the developmental changes in the RAS (in plasma, kidney, heart, and lung) and hemodynamic regulation in fetal sheep. TX was performed at 120 days of gestational age (dGA), and control fetuses were sham operated. Immediately before necropsy ( approximately 137 dGA), fetuses were infused with isoproterenol and the hemodynamic responses were noted. TX significantly decreased plasma thyroid hormone concentrations and renal renin mRNA and renal active renin levels but did not change fetal plasma active renin levels. TX decreased both angiotensin II receptor subtype 1 (AT1) mRNA and protein levels in kidney and lung but not in the left ventricle. TX also was associated with increased ANG II receptor subtype 2 (AT2) mRNA and protein at the 44-kDa band in kidney, whereas AT2 protein was decreased at the 78-kDa level in kidney and lung tissue only. TX fetuses had significantly lower basal mean arterial blood pressures (MAP) and heart rates than controls. Isoproterenol infusion decreased MAP in TX fetuses. These findings support the hypothesis that thyroid hormone is important in modulating maturation of RAS and cardiovascular function in the late-gestation fetal sheep.     

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.     

Autocrine regulation of internal anal sphincter tone by renin-angiotensin system: comparison with phasic smooth muscle

The myogenic control mechanisms that govern the basal tone in the internal anal sphincter (IAS) are not known. The present studies determined the autocrine regulation of ANG II in the IAS. The studies were performed in the freshly isolated smooth muscle cells (SMC) of the IAS. We determined the presence of ANG II precursor angiotensinogen (Angen), and the enzymes that convert it into ANG II, using functional, molecular biology, and immunocytochemical studies in rats. ANG II levels in the SMC were determined using ELISA. The IAS SMC generate ANG II at a rate severalfold higher than those from the adjoining smooth muscle of rectum (RSM). RT-PCR data show that IAS exclusively expresses significant higher levels of renin, Angen, and angiotensin-converting enzyme (ACE). These data were confirmed using Western blot analyses and immunocytochemistry. In the IAS SMC, H-77 (10 microM; renin inhibitor) and captopril (1 microM; ACE inhibitor) decreased the basal as well as Angen-increased levels of ANG II. The following functional data corroborate the role of renin-angiotensin system (RAS) in the IAS tone. Angen produced concentration-dependent shortening of the IAS SMC that was inhibited by H-77 and captopril. In addition, H-77 or captopril caused a concentration-dependent fall in the IAS tone vs. nontonic tissues. Basal tone in IAS is partially under the autocrine control of cellular RAS evident by the expression of mRNA coding Angen, renin, and ACE and translation to the respective proteins in the SMC.