Reciprocal changes in renal ACE/ANG II and ACE2/ANG 1-7 are associated with enhanced collecting duct renin in Goldblatt hypertensive rats

Alterations in the balance between ANG II/ACE and ANG 1-7/ACE2 in ANG II-dependent hypertension could reduce the generation of ANG 1-7 and contribute further to increased intrarenal ANG II. Upregulation of collecting duct (CD) renin may lead to increased ANG II formation during ANG II-dependent hypertension, thus contributing to this imbalance. We measured ANG I, ANG II, and ANG 1-7 contents, angiotensin-converting enzyme (ACE) and ACE2 gene expression, and renin activity in the renal cortex and medulla in the clipped kidneys (CK) and nonclipped kidneys (NCK) of 2K1C rats. After 3 wk of unilateral renal clipping, systolic blood pressure and plasma renin activity increased in 2K1C rats (n = 11) compared with sham rats (n = 9). Renal medullary angiotensin peptide levels were increased in 2K1C rats [ANG I: (CK = 171 ± 4; NCK = 251 ± 8 vs. sham = 55 ± 3 pg/g protein; P < 0.05); ANG II: (CK = 558 ± 79; NCK = 328 ± 18 vs. sham = 94 ± 7 pg/g protein; P < 0.001)]; and ANG 1-7 levels decreased (CK = 18 ± 2; NCK = 19 ± 2 pg/g vs. sham = 63 ± 10 pg/g; P < 0.001). In renal medullas of both kidneys of 2K1C rats, ACE mRNA levels and activity increased but ACE2 decreased. In further studies, we compared renal ACE and ACE2 mRNA levels and their activities from chronic ANG II-infused (n = 6) and sham-operated rats (n = 5). Although the ACE mRNA levels did not differ between ANG II rats and sham rats, the ANG II rats exhibited greater ACE activity and reduced ACE2 mRNA levels and activity. Renal medullary renin activity was similar in the CK and NCK of 2K1C rats but higher compared with sham. Thus, the differential regulation of ACE and ACE2 along with the upregulation of CD renin in both the CK and NCK in 2K1C hypertensive rats indicates that they are independent of perfusion pressure and contribute to the altered content of intrarenal ANG II and ANG 1-7.     

Effect of dietary sodium intake on the pressor reactivity to angiotensin II in rats with experimental cirrhosis of the liver

The present experiments were designed to evaluate vascular reactivity to angiotensin II in rats with experimental cirrhosis of the liver (induced with CCl4 and phenobarbital) before ascites appearance. The systemic pressor response to angiotensin II in conscious animals and the contractile effect of angiotensin II in isolated femoral arteries were studied. In addition, the effect of high sodium intake on these parameters was also analyzed. Both renin and aldosterone plasma concentrations were similar in control and cirrhotic rats on the normal or on the high sodium diet. Basal mean arterial pressure was higher in control rats than in cirrhotic rats on the normal sodium (116 +/- 4 vs. 101 +/- 4 mmHg (1 mmHg = 133.3 Pa), p less than 0.05) or on the high sodium diet (118 +/- 7 vs. 98 +/- 6 mmHg). No differences in plasma renin activity or plasma aldosterone were found between control and cirrhotic rats. Upon injection of angiotensin II, control rats show a dose-dependent increase in mean arterial pressure which is higher in high sodium than in normal sodium rats. Cirrhotic rats showed a lower hypertensive response to angiotensin II than their corresponding control rats. In addition, no difference between pressor responses to angiotensin II was observed when normal sodium and high sodium cirrhotic rats were compared. On application of angiotensin II, femoral arteries of control and cirrhotic rats exhibited a dose-dependent contraction. However, maximal contraction was higher in high sodium control rats (145 +/- 12 mg) than in normal sodium control rats (99 +/- 6 mg, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased renin excretion is associated with augmented urinary angiotensin II levels in chronic angiotensin II-infused hypertensive rats

Renin expression in principal cells of collecting ducts (CD) is upregulated in angiotensin II (ANG II)-dependent hypertensive rats; however, it remains unclear whether increased CD-derived renin undergoes tubular secretion. Accordingly, urinary levels of renin (uRen), angiotensinogen (uAGT), and ANG II (uANG II) were measured in chronic ANG II-infused Sprague-Dawley rats (80 ng/min for 14 days, n = 10) and sham-operated rats (n = 10). Systolic blood pressure increased in the ANG II rats by day 5 and continued to increase throughout the study (day 13; ANG II: 175 ± 10 vs. sham: 116 ± 2 mmHg; P < 0.05). ANG II infusion increased renal cortical and medullary ANG II levels (cortical ANG II: 606 ± 72 vs. 247 ± 43 fmol/g; P < 0.05; medullary ANG II: 2,066 ± 116 vs. 646 ± 36 fmol/g; P < 0.05). Although plasma renin activity (PRA) was suppressed in the ANG II-infused rats (0.3 ± 0.2 vs. 5.5 ± 1.8 ng ANG I·ml(-1)·h(-1); P < 0.05), renin content in renal medulla was increased (12,605 ± 1,343 vs. 7,956 ± 765 ng ANG I·h(-1)·mg(-1); P < 0.05). Excretion of uAGT and uANG II increased in the ANG II rats [uAGT: 1,107 ± 106 vs. 60 ± 26 ng/day; P < 0.0001; uANG II: 3,813 ± 431 vs. 2,080 ± 361 fmol/day; P < 0.05]. By day 13, despite suppression of PRA, urinary prorenin content increased in ANG II rats [15.7 ± 3 vs. 2.6 ± 1 × 10(-3) enzyme units excreted (EUE)/day, P < 0.01] as was the excretion rate of renin (8.6 ± 2 × 10(-6) EUE/day) compared with sham (2.8 ± 1 × 10(-6) EUE/day; P < 0.05). Urinary renin and prorenin protein levels examined by Western blot were augmented ～10-fold in the ANG II-infused rats. Concomitant AT(1) receptor blockade with candesartan prevented the increase. Thus, in ANG II-dependent hypertensive rats with marked PRA suppression, increased urinary levels of renin and prorenin reflect their augmented secretion by CD cells into the luminal fluid. The greater availability of renin and AGT in the urine reflects the capability for intratubular ANG II formation which stimulates sodium reabsorption in distal nephron segments.     

Roles of vasoconstrictor prostaglandins, COX-1 and -2, and AT1, AT2, and TP receptors in a rat model of early 2K,1C hypertension

Angiotensin (ANG) II activating type 1 receptors (AT(1)Rs) enhances superoxide anion (O(2)*(-)) and arachidonate (AA) formation. AA is metabolized by cyclooxygenases (COXs) to PGH(2), which is metabolized by thromboxane (Tx)A(2) synthase to TxA(2) or oxidized to 8-isoprostane PGF(2alpha) (8-Iso) by O(2)*(-). PGH(2), TxA(2), and 8-Iso activate thromboxane-prostanoid receptors (TPRs). We investigated whether blood pressure in a rat model of early (3 wk) two-kidney, one-clip (2K,1C) Goldblatt hypertension is maintained by AT(1)Rs or AT(2)Rs, driving COX-1 or -2-dependent products that activate TPRs. Compared with sham-operated rats, 2K,1C Goldblatt rats had increased mean arterial pressure (MAP; 120 +/- 4 vs. 155 +/- 3 mmHg; P < 0.001), plasma renin activity (PRA; 22 +/- 7 vs. 48 +/- 5 ng x ml(-1) x h(-1); P < 0.01), plasma malondialdehyde (1.07 +/- 0.05 vs. 1.58 +/- 0.16 nmol/l; P < 0.01), and TxB(2) excretion (26 +/- 4 vs. 51 +/- 7 ng/24 h; P < 0.01). Acute graded intravenous doses of benazeprilat (angiotensin-converting enzyme inhibitor) reduced MAP at 20 min (-36 +/- 5 mmHg; P < 0.001) and excretion of TxA(2) metabolites. Indomethacin (nonselective COX antagonist) or SC-560 (COX-1 antagonist) reduced MAP at 20 min (-25 +/- 5 and -28 +/- 7 mmHg; P < 0.001), whereas valdecoxib (COX-2 antagonist) was ineffective (-9 +/- 5 mmHg; not significant). Losartan (AT(1)R antagonist) or SQ-29548 (TPR antagonist) reduced MAP at 150 min (-24 +/- 6 and -22 +/- 3 mmHg; P < 0.001), whereas PD-123319 (AT(2)R antagonist) was ineffective. Acute blockade of TPRs, COX-1, or COX-2 did not change PRA, but TxB(2) generation by the clipped kidney was reduced by blockade of COX-1 and increased by blockade of COX-2. 2K,1C hypertension in rats activates renin, O(2)*(-), and vasoconstrictor PGs. Hypertension is maintained by AT(1)Rs and by COX-1, but not COX-2, products that activate TPRs.     

Subfornical organ differentially modulates baroreflex function in normotensive and two-kidney, one-clip hypertensive rats

During activation of the renin-angiotensin system, hindbrain circumventricular organs such as the area postrema have been implicated in modulating the arterial baroreflex. This study was undertaken to test the hypothesis that the subfornical organ (SFO), a forebrain circumventricular structure, may also modulate the baroreflex. Studies were performed in rats with two-kidney, one-clip (2K,1C) hypertension as a model of endogenously activated renin-angiotensin system. Baroreflex function was ascertained during ramp infusions of phenylephrine and nitroprusside in conscious sham-clipped and 5-wk 2K,1C rats with either a sham or electrolytically lesioned SFO. Lesioning significantly decreased mean arterial pressure in 2K,1C rats from 158 +/- 7 to 131 +/- 4 mmHg but not in sham-clipped rats. SFO-lesioned, sham-clipped rats had a significantly higher upper plateau and range of the renal sympathetic nerve activity-mean arterial pressure relationship compared with sham-clipped rats with SFO ablation. In contrast, lesioning the SFO in 2K,1C rats significantly decreased both the upper plateau and range of the baroreflex control of renal sympathetic nerve activity, but only the range of the baroreflex response of heart rate decreased. Thus, during unloading of the baroreceptors, the SFO differentially modulates the baroreflex responses in sham-clipped vs. 2K,1C rats. Since lesioning the SFO did not influence plasma angiotensin II (ANG II), the effects of the SFO lesion are not caused by changes in circulating levels of ANG II. These findings support a pivotal role for the SFO in the sympathoexcitation observed in renovascular hypertension and in baroreflex regulation of sympathetic activity in both normal and hypertensive states.     

Haemodynamic effects of angiotensin II in conscious, non-ascitic cirrhotic rats

The effect of angiotensin II (AII) on systemic and regional haemodynamics was studied in 18 control and 18 cirrhotic, non-ascitic conscious rats (CCl4/phenobarbital model). Cirrhotic rats were found to retain sodium and to have normal plasma renin and plasma aldosterone concentrations when compared with control animals. Cirrhotic rats showed an enhanced cardiac output (34.4 +/- 0.5 vs. 27.5 +/- 2.0 ml/min in controls) and decreased peripheral resistances (2.96 +/- 0.25 vs. 3.95 +/- 0.31 mm Hg/min/100 g/ml in controls) under basal conditions. When AII was administered cardiac output decreased by 10.7 +/- 1.2% in cirrhotic rats, whereas it increased in control animals (11.2 +/- 2%, p less than 0.005). The AII-induced increase in arterial pressure was lower in cirrhotic than in control rats. The renal blood supply was particularly impaired by AII in cirrhotics, with a maintained flow to other organs (muscle, testes). It is concluded that the response to AII is disturbed in rats with hepatic cirrhosis even in a stage without ascites and with plasma renin and aldosterone concentrations similar to those of control animals.     

Effect of elevated blood pressure, renin and aldosterone on renal sodium handling in two-kidney Goldblatt hypertensive rats

The effect of elevated blood pressure, renin and aldosterone on renal Na+ retention in two-kidney Goldblatt hypertensive rats were investigated. The technique involved retrograde perfusion from the renal veins via the kidneys, and then through the renal arteries and dorsal aorta. Sodium retention in the stenosed kidney of 7 and 30-60 days post-stenosis hypertensive rats was 82 and 70% higher than in normotensive sham-operated rats respectively. Sodium rention in the clipped kidney, 1 day post-stenosis, was insignificant. However, the contralateral kidney of the 1 day post-stenosis rats retained 27% more Na+. The 1 and 7 days post-stenosis rats had higher plasma aldosterone concentrations than controls, while the 30-60 days post-stenosis rats showed lower levels. The plasma renin activity of the 1 day post-stenosis rats showed 65% higher activity than the sham controls with no significant change in the 30-60 days post-stenosis. Therefore Na+ retention may be mediated by aldosterone in the 7 days post-stenosis rats. Natriuresis in the non-stenosed kidneys of both the 7 and 30-60 days post-stenosis rats may be modulated by an increase in filtration rate due to hypertrophy.     

Enalapril in subantihypertensive dosage attenuates kidney proliferation and functional recovery in normotensive ablation nephropathy of the rat

Most studies on the antiproliferative action of angiotensin converting enzyme inhibitors (ACEI) were performed in a rat hypertensive remnant kidney model with 5/6 kidney ablation which raised objections about the antihypertensive effect of ACEI and the influence of other antihypertensive drugs administered to remnant kidney control rats. To prevent these objections, a normotensive 4/6 remnant kidney model was elaborated and a subantihypertensive dosage of enalapril was used to evaluate its antiproliferative action. Subtotally nephrectomized rats (Nx) markedly increased the remnant kidney weight during a 4-week period and this rise was prevented by the treatment with enalapril (NxE) (Nx +297+/-35 mg vs. sham-operated +145+/-32 mg, p<0.001; NxE +154+/-35 mg vs. Nx p<0.001). While collagen concentration in the kidney cortex was not increased in sham-operated rats (Sham) in comparison with the control group (Ctrl) at the beginning of the study, the subsequent increase was significant in the Nx group and enalapril did not attenuate this increase (Sham 148+/-5 mg/100 g w.w. vs. Nx 164+/-2 mg/100 g w.w., p<0.01; NxE 161+/-4 mg/100 g w.w. vs. Sham p<0.05). The tubular protein/DNA ratio increase, which was significant in the Nx group, was inhibited by enalapril (Nx 26.2+/-10.5 vs. NxE 15.3+/-2.6, p<0.05). The protein/DNA ratio was much lower in glomeruli, with no significant changes in either the Nx or NxE groups. Serum urea concentrations were slightly higher in the Nx group than in the sham-operated group, but markedly elevated in the NxE group (Nx 10.71+/-0.76 mmol/l vs. Sham 6.10+/-0.33 mmol/l, p<0.001; NxE 28.9+/-2.6 mmol/l vs. Sham p<0.001). Creatinine concentrations in the Nx group were increased in comparison with the sham-operated group and markedly increased in the NxE group (Nx 63.7+/-3.56 micromol/l vs. Sham 37.2+/-2.84 micromol/l, p<0.001; NxE 107.0+/-5.2 micromol/l vs. Sham p<0.001). The clearance of creatinine was lower in the Nx group than in the sham-operated group and was markedly reduced in the NxE group (Nx 0.89+/-0.06 ml/min.g kidney wt. vs. Sham 1.05+/-0.16 ml/min x g kidney wt., p<0.01; NxE 0.58+/-0.029 ml/min x g kidney wt. vs. Sham, p<0.001). Enalapril improved proteinuria in comparison with the Nx group (NxE 5.6+/-0.6 mg/24 h vs. Nx 16.1+/-3.4 mg/24 h, p<0.05). Thus remnant kidney proliferation is substantial even in normotensive rats. It includes both proliferation and collagen accumulation with partial recovery of kidney weight and function, but is accompanied by enhanced proteinuria. Enalapril attenuates the proliferation and decreases proteinuria but prolongs kidney function recovery.     

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     

Role of the pituitary in the effects of tonin on adrenal secretion of the rat

Chronically catheterized conscious rats were infused intravenously with tonin at 2.4 and 12 micrograms x kg-1 x min-1 for 2 h. Plasma aldosterone concentration (PAC) at the end of the experiment was 11.2 +/- 2.4 ng% in controls, 8.5 +/- 2.8 ng% in rats infused with tonin at the lower rate, and 26.2 +/- 3.6 ng% (p less than 0.01 vs. controls) in rats infused at the higher rate. Plasma corticosterone (PC) was significantly higher (p less than 0.05) in the group infused at the high rate while plasma renin activity (PRA) was significantly reduced in this group of rats. Plasma angiotensin II (AII) concentration was similar in all three groups. PAC was elevated after tonin infusion in the presence of AII blockade. PAC in conscious sodium-depleted rats infused with tonin was not significantly changed, but PRA was significantly reduced (p less than 0.01). In chronically hypophysectomized rats, PAC remained unchanged by tonin infusion. The failure of tonin to stimulate aldosterone in hypophysectomized animals indicates a role of a pituitary hormone (probably ACTH) in the effect of tonin on adrenal secretion.     

Tetradecylthioacetic acid downregulates cyclooxygenase 2 in the renal cortex of two-kidney, one-clip hypertensive rats

The effect of tetradecylthioacetic acid (TTA) on the cyclooxygenase (COX) system was investigated in two-kidney, one-clip (2K1C) hypertensive rats. The systolic blood pressure (BP) was increased 6 wk after clipping to 183 +/- 4 vs.127 +/- 3 mmHg in TTA-treated 2K1C rats. The COX1 protein expression was not affected either by the 2K1C procedure or by TTA treatment. COX2 expression was upregulated in both kidneys, but to a greater extent in the clipped kidney. COX2 activity was 16 +/- 3% in control and 38 +/- 2% (P < 0.001) in the clipped kidney, and COX2 protein expression was 1.3 +/- 0.04 in control and 1.6 +/- 0.12 in the clipped kidney (P = 0.006). TTA reduced COX2 activity to control levels. Subcutaneously infusion of a COX2 inhibitor did not reduce BP. Peroxisome proliferator-activated receptors (PPARs) were detected in both kidneys, and PPARdelta was upregulated in the nonclipped kidney after TTA treatment. PGE2 in renal cortex was increased in 2K1C (31 +/- 0.3 in the clipped and 28 +/- 0.2 pg/ml nonclipped kidney, P < 0.001 compared with control). TTA lowered the PGE2 to control levels. Renal blood flow (RBF) response to exogenous ANG II injected in the control and nonclipped kidney was exaggerated after indomethacin treatment but unchanged in the nonclipped kidney of the K1C TTA group. Overall, these results indicate that, after 6 wk of treatment, TTA downregulated the COX2 activity, which have potentially important effects on the regulation of renal hemodynamics but does not explain TTAs ability to lower BP.     

Fetal uninephrectomy in male sheep alters the systemic and renal responses to angiotensin II infusion and AT1R blockade

Fetal uninephrectomy (uni-x) at 100 days of gestation results in compensatory nephrogenesis in the remaining kidney, resulting in a 30% reduction in total nephron number in male sheep. Recently, we showed that uni-x males at 6 mo of age have elevated arterial pressure, reduced renal blood flow (RBF), glomerular filtration rate (GFR), and low plasma renin levels (Singh R, Denton K, Bertram J, Jefferies A, Head G, Lombardo P, Schneider-Kolsky M, Moritz K. J Hypertens 27: 386-396, 2009; Singh R, Denton K, Jefferies A, Bertram J, Moritz K. Clin Sci (Lond) 118: 669-680, 2010). We hypothesized this was due to upregulation of the intrarenal renin-angiotensin system (RAS). In this study, renal responses to ANG II infusion and ANG II type 1 receptor (AT1R) blockade were examined in the same 6-mo-old male sheep. Uni-x animals had reduced levels of renal tissue and plasma renin and ANG II. Renal gene expression of renin, and gene and protein levels of AT1R and AT2R, were significantly lower in uni-x animals. In response to graded ANG II infusion, sham animals had the expected decrease in conscious RBF and GFR. Interestingly, the response was biphasic in uni-x sheep, with GFR initially decreasing, but then increasing at higher ANG II doses (34 ± 7%; P(group × treatment) < 0.001), due to a paradoxical decrease in renal vascular resistance (P(group × treatment) < 0.001). In response to AT1R blockade, while GFR and RBF responded similarly between groups, there was a marked increase in sodium excretion in uni-x compared with sham sheep (209 ± 35 vs. 25 ± 12%; P < 0.001). In conclusion, in 6-mo-old male sheep born with a single kidney, these studies demonstrate that this is a low-renin form of hypertension, in which responses to ANG II are perturbed and the intrarenal RAS is downregulated.     

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.     

Vaccarin administration ameliorates hypertension and cardiovascular remodeling in renovascular hypertensive rats

Sympathetic overdrive, activation of renin angiotensin systems (RAS), and oxidative stress are vitally involved in the pathogenesis of hypertension and cardiovascular remodeling. We recently identified that vaccarin protected endothelial cell function from oxidative stress or high glucose. In this study, we aimed to investigate whether vaccarin attenuated hypertension and cardiovascular remodeling. Two‐kidney one‐clip (2K1C) model rats were used, and low dose of vaccarin (10 mg/kg), high dose of vaccarin (30 mg/kg), captopril (30 mg/kg) were intraperitoneally administrated. Herein, we showed that 2K1C rats exhibited higher systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), left ventricular mass/body weight ratio, myocardial hypertrophy or fibrosis, media thickness, and media thickness to lumen diameter, which were obviously alleviated by vaccarin and captopril. In addition, both vaccarin and captopril abrogated the increased plasma renin, angiotensin II (Ang II), norepinephrine (NE), and the basal sympathetic activity. The AT1R protein expressions, NADPH oxidase subunit NOX‐2 protein levels and malondialdehyde (MDA) content were significantly increased, whereas superoxide dismutase (SOD) and catalase (CAT) activities were decreased in myocardium, aorta, and mesenteric artery of 2K1C rats, both vaccarin and captopril treatment counteracted these changes in renovascular hypertensive rats. Collectively, we concluded that vaccarin may be a novel complementary therapeutic medicine for the prevention and treatment of hypertension. The mechanisms for antihypertensive effects of vaccarin may be associated with inhibition of sympathetic activity, RAS, and oxidative stress.     

Angiotensin II infusion to the midgestation ovine fetus: effects on the fetal kidney

Renal and cardiovascular responses to an intravenous infusion of ANG II (1 microg/h) or saline for 3 days were examined in ovine fetuses at midgestation (75-85 days of gestation, term 150 days). ANG II caused an increase in fetal blood pressure (36 +/- 2 to 44 +/- 3 mmHg) and urine flow rate (8 +/- 2 to a maximum of 18 +/- 6 ml/h). Plasma renin concentrations decreased in ANG II-infused fetuses. Fetal fluids (amniotic and allantoic) did not differ in volume or composition between the groups when measured at postmortem. There was no difference in the expression levels of the mRNA for the angiotensin (AT(1) or AT(2)) receptors between the two groups when measured by an RNase protection assay. However, there was a significant decline in renin and AT(1) receptor gene expression when measured by a real-time polymerase chain reaction method. These results indicate that ANG II is diuretic and pressor when infused at midgestation. ANG II can feedback to decrease renin secretion by the fetal kidney, and this may occur by decreased renin gene expression.     

Quantitative assessment of tyrosine nitration of manganese superoxide dismutase in angiotensin II-infused rat kidney

Hypertension caused by angiotensin II is characterized by an increase in tissue oxidant stress as evidenced by increased quantities of reactive oxygen and nitrogen species. Manganese superoxide dismutase (MnSOD) is a key mitochondrial antioxidant enzyme that is inactivated in conditions of oxidant stress by reacting with peroxynitrite to form 3-nitrotyrosine in its active site. The increase in 3-nitrotyrosine content in MnSOD in the kidney of angiotensin II-infused rats was assessed in this study by immunohistochemistry, Western blotting, immunoprecipitation, and HPLC with UV detection (HPLC-UV). MnSOD activity decreased approximately 50% in angiotensin II-infused rat kidneys (24 +/- 4.6 vs. 11 +/- 5.2 U/mg) without a change in protein expression. Immunohistochemical staining showed 3-nitrotyrosine predominantly in distal tubules and collecting duct cells in the angiotensin II-infused rat kidneys. By two-photon microscopy, 3-nitrotyrosine colocalized with MnSOD. Total 3-nitrotyrosine content in kidney homogenates was increased in angiotensin II-infused rat kidney [3.2 +/- 1.9 (sham treated) vs. 9.5 +/- 2.3 ng/mg protein by HPLC-UV detection]. With tracer amounts of tyrosine-nitrated recombinant MnSOD, the most sensitive technique to detect tyrosine nitration of MnSOD was immunoprecipitation from tissue with anti-MnSOD antibody, followed by detection of 3-nitrotyrosine by Western blotting or HPLC. By HPLC, 3-nitrotyrosine content of kidney MnSOD increased 13-fold after angiotensin II infusion, representing an increase from approximately one-twentieth to one-fifth of the total 3-nitrotyrosine content in sham-treated and angiotensin II-infused rat kidney, respectively. Angiotensin II-induced hypertension is accompanied by increased tyrosine nitration of MnSOD, which, because it inactivates the enzyme, may contribute to increased oxidant stress in the kidney.     

Normal contractions triggered by I(Ca,L) in ventricular myocytes from rats with postinfarction CHF

Attenuated L-type Ca(2+) current (I(Ca,L)), or current-contraction gain have been proposed to explain impaired cardiac contractility in congestive heart failure (CHF). Six weeks after coronary artery ligation, which induced CHF, left ventricular myocytes from isoflurane-anesthetized rats were current or voltage clamped from -70 mV. In both cases, contraction and contractility were attenuated in CHF cells compared with cells from sham-operated rats when cells were only minimally dialyzed using high-resistance microelectrodes. With patch pipettes, cell dialysis caused attenuation of contractions in sham cells, but not CHF cells. Stepping from -50 mV, the following variables were not different between sham and CHF, respectively: peak I(Ca,L) (4.5 +/- 0.3 vs. 3.8 +/- 0.3 pApF(-1) at 23 degrees C and 9.4 +/- 0.5 vs. 8.4 +/- 0.5 pApF(-1) at 37 degrees C), the bell-shaped voltage-contraction relationship in Cs(+) solutions (fractional shortening, 15.2 +/- 1.0% vs. 14.3 +/- 0.7%, respectively, at 23 degrees C and 7.5 +/- 0.4% vs. 6.7 +/- 0.5% at 37 degrees C) and the sigmoidal voltage-contraction relationship in K(+) solutions. Caffeine-induced Ca(2+) release and sarcoplasmic reticulum Ca(2+)-ATPase-to-phospholamban ratio were not different. Thus CHF contractions triggered by I(Ca,L) were normal, and the contractile deficit was only seen in undialyzed cardiomyocytes stimulated from -70 mV.     

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.     

The Bradykinin B2 receptor is required for full expression of renal COX-2 and renin

Angiotensin converting enzyme (ACE) inhibition leads to increased levels of bradykinin, cyclooxygenase-2 (COX-2), and renin. Since bradykinin stimulates prostaglandin release, renin synthesis may be regulated through a kinin-COX-2 pathway. To test this hypothesis, we examined the impact of bradykinin B2 receptor (B2R) gene disruption in mice on kidney COX-2 and renin gene expression. Kidney COX-2 mRNA and protein levels were significantly lower in B2R-/- mice by 40-50%. On the other hand, renal COX-1 levels were similar in B2R-/- and +/+ mice. Renal renin protein was 61% lower in B2R-/- compared to B2R+/+ mice. This was accompanied by a significant reduction in renin mRNA levels in B2R-/- mice. Likewise, intrarenal angiotensin I levels were significantly lower in B2R-/- mice compared to B2R+/+ mice. In contrast, kidney angiotensin II levels were not different and averaged 261+/-16 and 266+/-15fmol/g in B2R+/+ and B2R-/- mice, respectively. Kidney angiotensinogen, AT1 receptor and ACE activity were not different between B2R+/+ and B2R-/- mice. The results of these studies demonstrate suppression of renal renin synthesis in mice lacking the bradykinin B2R and support the notion that B2R regulation of COX-2 participates in the steady-state control of renin gene expression.