Sexual Dimorphism in Urinary Angiotensinogen Excretion During Chronic Angiotensin II−Salt Hypertension

BackgroundThe intrarenal renin−angiotensin system contributes to hypertension by regulating sodium and water reabsorption throughout the nephron. Sex differences in the intrarenal components of the renin−angiotensin system have been involved in the greater incidence of high blood pressure and progression to kidney damage in males than females.ObjectiveThis study investigated whether there is a sex difference in the intrarenal gene expression and urinary excretion of angiotensinogen (AGT) during angiotensin II (Ang II)−dependent hypertension and high-salt (HS) diet.MethodsMale and female Sprague-Dawley rats were divided into 5 groups for each sex: Normal-salt control, HS diet (8% NaCl), Ang II−infused (80 ng/min), Ang II−infused plus HS diet, and Ang II−infused plus HS diet and treatment with the Ang II receptor blocker, candesartan (25 mg/L in the drinking water). Rats were evaluated for systolic blood pressure (SBP), kidney AGT mRNA expression, urinary AGT excretion, and proteinuria at different time points during a 14-day protocol.ResultsBoth male and female rats exhibited similar increases in urinary AGT, with increases in SBP during chronic Ang II infusion. HS diet greatly exacerbated the urinary AGT excretion in Ang II−infused rats; males had a 9-fold increase over Ang II alone and females had a 2.5-fold increase. Male rats displayed salt-sensitive SBP increases during Ang II infusion and HS diet, and female rats did not. In the kidney cortex, males displayed greater AGT gene expression than females during all treatments. During Ang II infusion, both sexes exhibited increases in AGT gene message compared with same-sex controls. In addition, HS diet combined with Ang II infusion exacerbated the proteinuria in both sexes. Concomitant Ang II receptor blocker treatment during Ang II infusion and HS diet decreased SBP and urinary AGT similarly in both sexes; however, the decrease in proteinuria was greater in the females.ConclusionDuring Ang II−dependent hypertension and HS diet, higher intrarenal renin-angiotensin system activation in males, as reflected by higher AGT gene expression and urinary excretion, indicates a mechanism for greater progression of high blood pressure and might explain the sex disparity in development of salt-sensitive hypertension.     

Intrarenal oxidative stress and augmented angiotensinogen are precedent to renal injury in Zucker diabetic fatty rats

The Zucker diabetic fatty (ZDF) rat is a model of type II diabetes and metabolic syndrome based on impaired glucose tolerance caused by the inherited insulin-resistance gene. The ZDF rat exhibits progressive nephropathy; however, the detailed mechanisms have remained unclear. This study was performed to examine the possible involvement of enhanced intrarenal angiotensinogen in the development of renal injury in ZDF rats. Genetic pairs of male ZDF rats and control lean rats (N=6 each) were maintained from 12 to 17 weeks of age. At 17 weeks of age, fasting blood glucose and urinary 8-isoprostane levels were significantly higher in ZDF rats compared with the controls. Systolic blood pressure progressively increased in ZDF rats from 120+/-1 to 137+/-1 mmHg during this period. In contrast, systolic blood pressure did not increase in the controls. Kidney angiotensinogen protein levels were significantly increased in ZDF rats compared with the controls (1.83+/-0.34 vs. 1.00+/-0.17, relative ratio). Expression of angiotensin II type 1a receptor mRNA was similar between these groups. The measured indices of renal damage in the present study (glomerular sclerosis, interstitial expansion, glomerular macrophage infiltration, and renal arterial proliferation) were not significantly increased at this stage in ZDF rats. However, we previously showed that the increased reactive oxygen species-related angiotensinogen enhancement plays an important role in the development of renal injury in a genetic salt-sensitive hypertension. Thus, the present data suggest that elevated reactive oxygen species and reactive oxygen species-associated augmentation of intrarenal angiotensinogen may initiate the development of renal injury in ZDF rats.     

Detailed Localization of Augmented Angiotensinogen mRNA and Protein in Proximal Tubule Segments of Diabetic Kidneys in Rats and Humans

In the intrarenal renin-angiotensin system, angiotensinogen levels are well known to be increased in diabetes, and these enhanced intrarenal angiotensinogen levels may initiate the development and accelerate the progression of diabetic nephropathy. However, the specific localization of the augmented angiotensinogen in proximal tubule segments in diabetes is still unknown. We investigated the detailed localization of angiotensinogen in 3 proximal tubule segments in the diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats and the control Long-Evans Tokushima Otsuka (LETO) rats. We also prepared OLETF rats treated with angiotensin II type 1 receptor blocker, olmesartan or with a combination of vasodilator agents. Moreover, biopsied samples of human kidney cortex were used to confirm the results of animal studies. We examined the co-localization of angiotensinogen with segment-specific markers by double staining using fluorescence in situ hybridization and/or immunofluorescence. Angiotensinogen mRNA expression was barely detectable in segment 1. In segment 3, the area of angiotensinogen mRNA expression was augmented in the OLETF rats compared with the LETO rats. Angiotensinogen protein expression areas in segments 1 and 3 were also increased in the OLETF rats compared with the LETO rats. Chronic treatment with olmesartan ameliorated these areas of augmented angiotensinogen expression. Biopsied human kidney samples showed similar results. These data suggest that the augmented angiotensinogen mRNA levels in segment 3 and angiotensinogen protein levels in segments 1 and 3 may contribute to the progression of diabetic nephropathy.     

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 converting enzyme inhibition in Dahl salt-sensitive rats

Angiotensin II has previously been reported to have in vivo and in vitro cardiac hypertrophic effects. We used the salt-sensitive Dahl rat genetic strain to separate mechanical (pressure overload) vs. hormonal (renin-angiotensin system) input in cardiac hypertrophy. Blood pressure was significantly increased and left ventricular hypertrophy, as indexed by LV/BW ratios, was present at 7 and 15 days in rats receiving 4% and 8% NaCl compared to the 1% controls. There was no effect of the angiotensin converting enzyme inhibitor, enalapril maleate, on lowering the blood pressure in 8% NaCl-treated animals, however, there was a significant reduction in LV/BW ratio in 8% NaCl-treated animals that received this drug. Left ventricular angiotensinogen mRNA activity was significantly reduced in rats receiving 4% and 8% NaCl. In this model of hypertension the cardiac hypertrophy which develops is largely dependent on mechanical forces though there remains a significant contribution to this process from either circulating or localized angiotensin II production. Regulation of angiotensinogen gene expression in the hypertrophied left ventricle suggests that volume and electrolyte control of angiotensinogen gene expression in the heart and/or hereditary factors are predominant in the control of regulation of this gene in the left ventricle of Dahl rats.     

Effects of tempol on renal angiotensinogen production in Dahl salt-sensitive rats

We have recently reported that Dahl salt-sensitive rats (DS) on high salt diet (HS) have an inappropriate augmentation of intrarenal angiotensinogen. Recent studies also reported that the augmented superoxide anion formation plays important roles in this animal model of hypertension. This study was performed to address the hypothesis that an inappropriate augmentation of intrarenal angiotensinogen by HS is caused by the augmented reactive oxygen species. Male DS (200-220 g) were maintained on low salt diet LS (N = 7) or HS (N = 27) for 4 weeks. The HS group was subdivided into three subgroups to receive null (N = 12), superoxide dismutase mimetic, tempol (3 mmol/l, N = 8), or vasodilator, hydralazine (0.5 mmol/l, N = 7) in drinking water during the period. Systolic BP was significantly increased in the DS+HS group compared to the DS+LS group (184+/-7 mmHg vs. 107+/-5 at 4-week). Tempol or hydralazine treatment equivalently attenuated the hypertension (128+/-3 and 127+/-5 at 4-week, respectively). Urinary excretion of thiobarbituric acid reactive substances at 4-week was significantly increased in the DS+HS group compared to the DS+LS group (0.66+/-0.05 micromol/day vs. 0.14+/-0.01). Tempol treatment prevented this effect (0.24+/-0.04) but hydralazine treatment only partially prevented the effect (0.40+/-0.03). Kidney angiotensinogen levels, measured by Western blot analysis, were significantly increased in the DS+HS group compared to the DS+LS group (32+/-5 densitometric units vs. 21+/-1). Tempol (14+/-3) but not hydralazine (32+/-5) treatment prevented the intrarenal angiotensinogen augmentation. The evidence suggests that the enhanced intrarenal angiotensinogen in DS challenged with HS is associated with the augmented reactive oxygen species.     

The predominant role of brain angiotensinogen and angiotensin in environmentally induced hypertension

Rats exposed chronically to a cold environment (5 degrees C/4 degrees F) develop hypertension. This cold-induced hypertension (CIH) is a non-genetic, non-pharmacological, non-surgical model of environmentally induced hypertension in rats. The renin-angiotensin system (RAS) appears to play a role in both initiating and/or maintaining the high blood pressure in CIH. The goal of the present study was to evaluate the role of central and peripheral circulating RAS components, angiotensinogen (AGT), angiotensin-converting enzyme (ACE) and angiotensin (Ang) II, in CIH. Seventy-two Sprague-Dawley adult male rats were used. Thirty-six rats were kept in cold room at 5 degrees C while the other 36 were at 24 degrees C as controls for 5 weeks. Systolic blood pressure (SBP) was recorded by tail cuff. The SBP was increased in rats exposed to cold within 1 week, and this increase was significant for the next 2-5 weeks of the cold exposure (p<0.01). Three subgroups of the cold-treated and control rats (n=12) were sacrificed at 1, 3 and 5 weeks. The brain and liver were removed and plasma was saved. The AGT mRNA significantly increased in the hypothalamus and liver in cold-treated rats from the first week of exposure to cold, and was maintained throughout the time of exposure to cold (n=4, p<0.01). The AGT protein levels in the brain, liver and plasma did not differ significantly between cold-treated and control rats (p>0.05, n=4). The hypothalamic Ang II levels were significantly increased, whereas plasma Ang II levels significantly decreased, in the rats of 5 weeks of cold exposure (n=8, p<0.05). Plasma ACE significantly increased in the rats of 1 week of cold exposure (p<0.05, n=12). The results show differential regulation of RAS components, AGT, ACE and Ang II, between brain and periphery in cold-exposed rats. We conclude that the exposure to low temperature initially increases plasma RAS but with continuous exposure to cold, the brain RAS maintains the hypertension, probably by sustained sympathetic activation, which would provide increased metabolism but also vasoconstriction leading to hypertension.     

Renal functional responses to selective intrarenal renin inhibition in Cyp1a1-Ren2 transgenic rats with ANG II-dependent malignant hypertension

Angiotensin (ANG) II-dependent hypertension is characterized by increases in intrarenal ANG II levels, derangement in renal hemodynamics, and augmented tubular sodium reabsorptive capability. Increased nephron expression of renin-angiotensin system components, such as angiotensinogen by proximal tubule cells and renin by collecting duct principal cells, has been associated with an augmented ability of the kidney to form ANG II in hypertensive states. However, the contribution of de novo intrarenal ANG II production to the development and maintenance of ANG II-dependent hypertension remains unclear. The present study was performed to determine the effects of selective intrarenal renin inhibition on whole kidney hemodynamics and renal excretory function in Cyp1a1-Ren2 rats with ANG II-dependent malignant hypertension in the absence of the confounding influence of associated reductions in mean arterial pressure (MAP). Male Cyp1a1-Ren2 transgenic rats were induced to develop malignant hypertension, anesthetized, and surgically prepared for intrarenal administration of the direct renin inhibitor aliskiren (0.01 mg/kg). Following acute aliskiren treatment, urine flow and sodium excretion increased (10.5 ± 1.1 to 15.9 ± 1.9 μl/min, P < 0.001; 550 ± 160 to 1,370 ± 320 neq/min, P < 0.001, respectively) and ANG II excretion decreased (120 ± 30 to 63 ± 17 fmol/h, P < 0.05). There were no significant changes in MAP, glomerular filtration rate, estimated renal plasma flow, plasma ANG II levels, or protein excretion. The present findings demonstrate that selective renal renin inhibition elicits diuretic and natriuretic responses in Cyp1a1-Ren2 rats with ANG II-dependent malignant hypertension. Elevated intraluminal ANG II levels likely act to augment tubular reabsorptive function and, thereby, contribute to the elevated blood pressure in Cyp1a1-Ren2 rats with ANG II-dependent malignant hypertension.     

Enhanced response of plasma prolactin to metoclopramide during chronic converting enzyme inhibition

The effect of chronic converting enzyme inhibition with enalapril on the PRA, PRL and plasma aldosterone responses to metoclopramide was studied in 10 patients with mild to moderate essential hypertension. Enalapril reduced supine blood pressure and increased heart rate significantly. PRA and urinary sodium excretion rose significantly. PRA levels did not change after metoclopramide neither during placebo nor during enalapril. The aldosterone response to metoclopramide was not altered by enalapril, indicating that this response is independent of the renin-angiotensin system. The PRL response to metoclopramide was considerably enhanced after 4 weeks of treatment with enalapril. It is proposed that enalapril, by decreasing the formation of angiotensin II, increases the prolactin reserve.     

Endogenous angiotensin II regulates hepatic angiotensinogen production

We have investigated the effects of endogenous angiotensin II (ANG II) on hepatic angiotensinogen mRNA levels in rats. Changes in endogenous ANG II were induced by various sodium intakes (standard-, low-, and high-sodium) or by enalapril treatment. In a low sodium state for 2 weeks, angiotensinogen mRNA levels and plasma ANG II concentration increased 1.3-fold and 1.6-fold compared to those in standard sodium state, respectively. In a high sodium state, angiotensinogen mRNA levels and plasma ANG II concentration decreased by 42% and 56% compared to the standard sodierm state, respectively. Four hours after treatment with enalapril (3 mg/kg), angiotensinogen mRNA level and plasma ANG II concentration decreased by 25% and 12% compared to the standard sodium state, respectively. There was a close correlation between angiotensinogen mRNA level and plasma ANG II concentration (r = 0.79, P less than 0.01). These results suggest that endogenous ANG II may play an important role in the regulation of hepatic angiotensinogen synthesis.     

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.     

Analysis of the renin-angiotensin system during fasting in adult male rabbits.

Caloric deprivation for 3 days in adult male rabbits induced significant increases in daily urinary Na+ excretion, urinary volume and fluid intake as previously reported. These changes were accompanied by: (a) a significant reduction in plasma renin concentration; (b) an unchanged plasma renin activity; (c) a marked increase in the plasma angiotensinogen concentration; (d) a significant reduction in plasma angiotensin I; and (e) a significant increase in plasma angiotensin II. In a separate group of adult male rabbits, 3 days of caloric deprivation significantly increased the amount of converting enzyme in pulmonary parenchymal tissue. These findings correlate with the previously reported enhancement of mineralocortical hormone secretion and limiting effect of the latter on the natriuresis of caloric withdrawal. Since the increased mineralocortical hormone secretion does not prevent the natriuresis, the possibility that these striking changes in the components of the renin-angiotensin system during caloric deprivation may exert intrarenal effects is discussed.     

High Salt Intake Damages the Heart through Activation of Cardiac (Pro) Renin Receptors Even at an Early Stage of Hypertension

Objective

It has not yet been fully elucidated whether cardiac tissue levels of prorenin, renin and (P)RR are activated in hypertension with a high salt intake. We hypothesized that a high salt intake activates the cardiac tissue renin angiotensin system and prorenin-(pro)renin receptor system, and damages the heart at an early stage of hypertension.

Methods

Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) received regular (normal-salt diet, 0.9%) and high-salt (8.9%) chow for 6 weeks from 6 to 12 weeks of age. The systolic blood pressure, plasma renin activity (PRA) and plasma angiotensin II concentration were measured, and the protein expressions of prorenin, (pro)renin receptor, angiotensinogen, angiotensin II AT1 receptor, ERK1/2, TGF-β, p38MAPK and HSP27 in the myocardium were investigated. The cardiac function was assessed by echocardiography, and histological analysis of the myocardium was performed.

Results

The high-salt diet significantly increased the systolic blood pressure, and significantly reduced the PRA and plasma angiotensin II concentration both in the WKYs and SHRs. Cardiac expressions of prorenin, renin, (P)RR, angiotensinogen, angiotensin II AT1 receptor, phosphorylated (p)-ERK1/2, p-p38MAPK, TGF-β and p-HSP27 were significantly increased by the high salt diet both in the WKYs and SHRs. The high-salt diet significantly increased the interventricular septum thickness and cardiomyocyte size, and accelerated cardiac interstitial and perivascular fibrosis both in the WKYs and SHRs. On the other hand, dilatation of left ventricular end-diastolic dimension and impairment of left ventricular fractional shortening was shown only in salt loaded SHRs.

Conclusion

The high-salt diet markedly accelerated cardiac damage through the stimulation of cardiac (P)RR and angiotensin II AT1 receptor by increasing tissue prorenin, renin and angiotensinogen and the activation of ERK1/2, TGF-β, p38MAPK and HSP27 under higher blood pressure.     

Responsiveness vs. basal activity of plasma ANG II as a determinant of arterial pressure salt sensitivity

Infusion of angiotensin II (ANG II) causes salt-sensitive hypertension. It is unclear whether this is due to the body's inability to suppress ANG II during increased salt intake or, rather, an elevated basal level of plasma ANG II itself. To distinguish between these mechanisms, Sprague-Dawley rats were instrumented with arterial and venous catheters for measurement of arterial pressure and infusion of drugs, respectively. The sensitivity of arterial pressure to salt was measured in four groups with the following treatments: 1) saline control (Con, n = 12); 2) administration of the angiotensin-converting enzyme inhibitor enalapril to block endogenous ANG II (ANG-Lo, n = 10); 3) administration of enalapril and 5 ng.kg(-1).min(-1) ANG II to clamp plasma ANG II at normal levels (ANG-Norm, n = 10); and 4) administration of enalapril and 20 ng.kg(-1).min(-1) ANG II to clamp ANG II at high levels (ANG-Hi, n = 10). Rats ingested a 0.4% NaCl diet for 3 days and then a 4.0% NaCl diet for 11 days. Arterial pressure of rats fed the 0.4% NaCl diet was lower in ANG-Lo (84 +/- 2 mmHg) compared with Con (101 +/- 3 mmHg) and ANG-Norm (98 +/- 4 mmHg) groups, whereas ANG-Hi rats were hypertensive (145 +/- 4 mmHg). Salt sensitivity was expressed as the change in arterial pressure divided by the change in sodium intake on the last day of the 4.0% NaCl diet. Salt sensitivity (in mmHg/meq Na) was lowest in Con rats (0.0 +/- 0.1) and progressed from ANG-Lo (0.8 +/- 0.2) to ANG-Norm (1.5 +/- 0.5) to ANG-Hi (3.5 +/- 0.5) rats. We conclude that the major determinant of salt sensitivity of arterial pressure is the basal level of plasma ANG II rather than the responsiveness of the renin-angiotensin system.     

Regulation of angiotensinogen by angiotensin II in mouse primary astrocyte cultures

Astrocytes are the major source of angiotensinogen in the brain and play an important role in the brain renin-angiotensin system. Regulating brain angiotensinogen production alters blood pressure and fluid and electrolyte homeostasis. In turn, several physiological and pathological manipulations alter expression of angiotensinogen in brain. Surprisingly, little is known about the factors that regulate astrocytic expression of angiotensinogen. There is evidence that angiotensinogen production in both hepatocytes and cardiac myocytes can be positively regulated via the angiotensin type 1 receptor, but this effect has not yet been studied in astrocytes. Therefore, the aim of this project was to establish whether angiotensin II modulates angiotensinogen production in brain astrocytes. Primary astrocyte cultures, prepared from neonatal C57Bl6 mice, expressed angiotensinogen measured by immunocytochemistry and real-time PCR. Using a variety of approaches we were unable to identify angiotensin receptors on cultured astrocytes. Exposure of cultured astrocytes to angiotensin II also did not affect angiotensinogen expression. When astrocyte cultures were transduced with the angiotensin type 1A receptor, using adenoviral vectors, angiotensin II induced a robust down-regulation (91.4% ± 1.8%, p < 0.01, n = 4) of angiotensinogen gene expression. We conclude that receptors for angiotensin II are present in extremely low levels in astrocytes, and that this concurs with available data in vivo. The signaling pathways activated by the angiotensin type 1A receptor are negatively coupled to angiotensinogen expression and represent a powerful pathway for decreasing expression of this protein, potentially via signaling pathways coupled to Gα(q/11) .     

Activation of the systemic and adipose renin-angiotensin system in rats with diet-induced obesity and hypertension

In obesity-related hypertension, activation of the renin-angiotensin system (RAS) has been reported despite marked fluid volume expansion. Adipose tissue expresses components of the RAS and is markedly expanded in obesity. This study evaluated changes in components of the adipose and systemic RAS in diet-induced obese hypertensive rats. RAS was quantified in adipose tissue and compared with primary sources for the circulating RAS. Male Sprague-Dawley rats were fed either a low-fat (LF; 11% kcal as fat) or moderately high-fat (32% kcal as fat) diet for 11 wk. After 8 wk, rats fed the moderately high-fat diet segregated into obesity-prone (OP) and obesity-resistant (OR) groups based on their body weight gain (body weight: OR, 566 +/- 10; OP, 702 +/- 20 g; P < 0.05). Mean arterial blood pressure was increased in OP rats (LF: 97 +/- 2; OR: 97 +/- 2; OP: 105 +/- 1 mmHg; P < 0.05). Quantification of mRNA expression by real-time PCR demonstrated a selective increase (2-fold) in angiotensinogen gene expression in retroperitoneal adipose tissue from OP vs. OR and LF rats. Similarly, plasma angiotensinogen concentration was increased in OP rats (LF: 390 +/- 48; OR: 355 +/- 24; OP: 530 +/- 22 ng/ml; P < 0.05). In contrast, other components of the RAS were not altered in OP rats. Marked increases in the plasma concentrations of angiotensin peptides were observed in OP rats (angiotensin II: LF: 95 +/- 31; OR: 59 +/- 20; OP: 295 +/- 118 pg/ml; P < 0.05). These results demonstrate increased activity of the adipose and systemic RAS in obesity-related hypertension.     

The adipose-tissue renin-angiotensin-aldosterone system: role in the metabolic syndrome?

Overfeeding of rodents leads to increased local formation of angiotensin II due to increased secretion of angiotensinogen from adipocytes. Whereas angiotensin II promotes adipocyte growth and preadipocyte recruitment, increased secretion of angiotensinogen from adipocytes also directly contributes to the close relationship between adipose-tissue mass and blood pressure in mice. In contrast, angiotensin II acts as an antiadipogenic substance in human adipose tissue, and the total increase in adipose-tissue mass may be more important in determining human plasma angiotensinogen levels than changes within the single adipocyte. However, as increased local formation of angiotensin II in adipose tissue may be increased especially in obese hypertensive subjects, a contribution of the adipose-tissue renin-angiotensin system to the development of insulin resistance and hypertension is conceivable in humans, but not yet proven. Insulin resistance may be aggravated by the inhibition of preadipocyte recruitment, which results in the redistribution of triglycerides to the liver and skeletal muscle, and blood pressure may be influenced by local formation of angiotensin II in perivascular adipose tissue. Thus, although the mechanisms are still speculative, the beneficial effects of ACE-inhibition and angiotensin-receptor blockade on the development of type 2 diabetes in large clinical trials suggest a pathophysiological role of the adipose-tissue renin-angiotensin system in the metabolic syndrome.     

The effects of intracerebroventricular administration of tonin on water drinking and blood pressure in rats

Intraventricular administration of tonin, an enzyme which forms angiotensin II directly from a natural protein substrate (angiotensinogen), stimulated water drinking and increased systemic blood pressure in rats. These responses were abolished by the simultaneous administration of an angiotensin II analogue, but unaffected by an angiotensin I- converting enzyme inhibitor. We confirmed, in vitro, that angiotensin II was generated when the brain homogenate was incubated with tonin in the presence of DFP and EDTA. These results indicate that the central effects of tonin on water drinking and systemic blood pressure are mediated via the direct formation of angiotensin II in the brain, and suggest the possibility that the tonin-angiotensin II system in the central nervous system might be important in controlling water balance and blood pressure.     

Evidence for an intrarenal renin-angiotensin system in the rainbow trout, Oncorhynchus mykiss

Physiological and molecular approaches were used to investigate the existence of an intrarenal renin-angiotensin system (RAS) in rainbow trout. Inhibition of angiotensin-converting enzyme by captopril (5 x 10(-4 )M) rapidly decreased vascular resistance of the trunk of the trout, perfused at 19 mmHg, resulting in an increased perfusate flow rate and a decreased intrarenal dorsal aortic pressure. A profound diuresis occurred in the in situ perfused kidney and reflected both increased glomerular filtration rates and decreased water reabsorption (osmolyte reabsorption was unchanged). Renal and vascular parameters recovered once captopril treatment was stopped. Diuretic and vascular effects of captopril on the in situ trout kidney concur with an inhibition of known vasoconstrictor and antidiuretic actions of angiotensin II. However, at a higher perfusion pressure (28 mmHg), captopril had no effect on intrarenal aortic pressure or perfusate and urine flow rates, suggesting that the trout intrarenal RAS is activated by low perfusion pressures/flows. Existence of the renal RAS in trout was further supported by evidence for angiotensinogen gene expression in kidney as well as liver.