Involvement of angiotensin II in development of spontaneous nephrosis in Dahl salt-sensitive rats

Hemodynamic effect of angiotensin II receptor blockade in postmenopausal women on a high-sodium diet: A double-blind, randomized, placebo-controlled study

BACKGROUND

Hypertension becomes increasingly prevalent after menopause. Postmenopausal women are more responsive to salt than premenopausal women, and they have been reported to develop marked renal vasoconstriction on a high-sodium diet.

OBJECTIVE

The aim of this study was to assess whether angiotensin II receptor blockade can restore a normal pattern of renal response to salt in postmenopausal women on a high-sodium diet. We also assessed segmental renal sodium handling in that population.

METHODS

Normotensive and hypertensive postmenopausal women not receiving hormone replacement therapy were enrolled in this prospective, double-blind, placebo-controlled, crossover study. They were assigned to receive irbesartan 150 mg or placebo for 6 weeks; the sequence in which they received irbesartan or placebo was randomized. During the last week of treatment, they received a high-sodium diet (250 mmol/d). Ambulatory blood pressure (ABP), glomerular filtration rate (GFR), and effective renal plasma flow (ERPF) were measured using sinistrin and para-amino-hippurate clearances. Renal sodium handling was assessed by measuring endogenous lithium clearance on day 7 of the high-salt diet.

RESULTS

Nineteen women (mean age, 54.7 years; range, 43-72 years; 7 normotensive subjects [mean age, 53.4 years; range, 47-61 years] and 12 hypertensive subjects [mean age, 55.4 years; range, 43-72 years]) were included in the study. When the data for all 19 subjects were pooled, ABP was significantly lower with irbesartan than placebo both during the day (120 [3]/79 [2] vs 127 [3]/85 [2] mm Hg; both, P < 0.01) and at night (systolic BP, 107 [4] vs 111 [4] mm Hg [P < 0.01] and diastolic BP, 71 [2] vs 75 [2] mm Hg [P < 0.05]). Compared with placebo, irbesartan was not associated with a significant change in GFR in either the normotensive or the hypertensive women. When the data for all 19 subjects were pooled, irbesartan was associated with a significant increase in ERPF compared with placebo (372 [21] vs324 [18] mL/min · 1.73 m(2); P < 0.05). When the hypertensive and normotensive women were considered separately, the effect was more pronounced in the hypertensive women than in the normotensive women, but the changes did not reach statistical significance. When the data for all subjects were pooled, irbesartan was associated with a significant increase in daytime urinary sodium excretion compared with placebo (135 [13] vs 106 [13] μmol/min; P < 0.05) and a significant decrease at night (109 [13] vs 136 [19] μmol/min; P < 0.05). Fractional excretion of lithium (FELi), an inverse marker of proximal sodium reabsorption, increased significantly during the daytime with irbesartan compared with placebo (47% [6.5%] vs 35% [4.7%]; P < 0.05). At nighttime, FELi was significantly higher in the hypertensive subjects receiving irbesartan compared with placebo (43% [7.2%] vs 29% [6.5%]; P < 0.05). The fractional distal reabsorption of sodium did not change significantly with irbesartan compared with placebo.

CONCLUSIONS

The results from this study suggest that angiotensin II receptor blockade had a favorable impact on BP, renal hemodynamics, and renal sodium handling in these salt-replete postmenopausal women. Blockade of the renin-angiotensin system restored the normal pattern of renal response to high sodium intake in these women.

Involvement of heparan sulfate in the renoprotective effects of imidapril, an angiotensin-converting enzyme inhibitor, in diabetic db/db mice

We investigated the renoprotective effects of imidapril hydrochloride ((-)-(4 S)-3-[(2 S)-2-[[(1 S)-1-ethoxycarbonyl-3-phenylpropyl] amino] propionyl]-1-methyl-2-oxoimidazolidine-4-carboxylic acid hydrochloride, imidapril), an angiotensin-converting enzyme inhibitor, in a diabetic animal model. We used BKS.Cg-+Lepr(db)/+Lepr(db) (db/db) mice, a genetic animal model of obese type 2 diabetes. Diabetic db/db mice suffered from glomerular hyperfiltration, albuminuria and hypoalbuminemia. Oral administration of 5 mg/kg/day of imidapril for 3 weeks suppressed renal hyperfiltration, reduced albuminuria and normalized hypoalbuminemia. Imidapril did not influence body weights, blood pressure or blood glucose concentrations in db/db mice. Urinary excretion of heparan sulfate (HS) in non-treated 11-week-old db/db mice was significantly lower than that in age-matched non-diabetic db/+m mice. HS is a component of HS proteoglycans, which are present in glomerular basement membranes and glycocalyx of cell surfaces. Reduced urinary HS excretion indicated glomerular HS loss in db/db mice. Imidapril increased urinary excretion of HS to concentrations observed in db/+m mice, indicating that imidapril prevented the loss of renal HS. These results suggest that imidapril ameliorates renal hyperfiltration and loss of renal contents of HS. Improvement of filtration function and maintenance of HS, which is an important structural component of glomeruli, may contribute to renoprotective effects of imidapril.

Long-Term Effect of Imidapril Hydrochloride Compared With Dilazep Hydrochloride Administration on Blood Pressure and Renal Function in Patients With Chronic Glomerulonephritis

The objective of the present study was to compare the effects of imidapril hydrochloride, an angiotensin converting enzyme inhibitor, and dilazep hydrochloride, an antiplatelet agent, on urinary protein excretion and renal function in patients with chronic glomerulonephritis. Imidapril (2.5 or 5 mg/day) or dilazep (300 or 450 mg/day) was administered for 3 years. Blood pressure, proteinuria, and renal function were measured before and during the treatment. In the group administered imidapril (n = 11), urinary protein decreased by approximately 50% (2.16 +/- 1.57 versus 0.90 +/- 0.53 g/g Cr, P < 0.01) and blood pressure by 14/10 mmHg (139.6 +/- 17.4/93.6 +/- 8.7 mmHg versus 122.7 +/- 10.5/81.8 +/- 9.9 mmHg, P < 0.01) and both remained at low levels during the three years of treatment. No correlation was observed between the extent of blood pressure reduction and changes in urinary protein. Serum creatinine concentrations did not change significantly (1.3 +/- 0.3 versus 1.3 +/- 0.3 mg/dL, NS). In the dilazep group (n = 12), there were no significant changes in blood pressure, urinary protein, or serum creatinine. These findings demonstrate that imidapril reduces proteinuria and contributes to preserve renal function, suggesting its usefulness in the treatment of patients with chronic glomerulonephritis.

Protection of the cardiovascular system by imidapril, a versatile angiotensin-converting enzyme inhibitor

Imidapril hydrochloride (imidapril) is a long-acting, non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor, which has been used clinically in the treatment of hypertension, chronic congestive heart failure (CHF), acute myocardial infarction (AMI), and diabetic nephropathy. It has the unique advantage over other ACE inhibitors in causing a lower incidence of dry cough. After oral administration, imidapril is rapidly converted in the liver to its active metabolite imidaprilat. The plasma levels of imidaprilat gradually increase in proportion to the dose, and decline slowly. The time to reach the maximum plasma concentration (T(max)) is 2.0 h for imidapril and 9.3 h for imidaprilat. The elimination half-lives (t(1/2)) of imidapril and imidaprilat is 1.7 and 14.8 h, respectively. Imidapril and its metabolites are excreted chiefly in the urine. As an ACE inhibitor, imidaprilat is as potent as enalaprilat, an active metabolite of enalapril, and about twice as potent as captopril. In patients with hypertension, blood pressure was still decreased at 24 h after imidapril administration. The antihypertensive effect of imidapril was dose-dependent. The maximal reduction of blood pressure and plasma ACE was achieved with imidapril, 10 mg once daily, and the additional effect was not prominent with higher doses. When administered to patients with AMI, imidapril improved left ventricular ejection fraction and reduced plasma brain natriuretic peptide (BNP) levels. In patients with mild-to-moderate CHF [New York Heart Association (NYHA) functional class II-III], imidapril increased exercise time and physical working capacity and decreased plasma atrial natriuretic peptide (ANP) and BNP levels in a dose-related manner. In patients with diabetic nephropathy, imidapril decreased urinary albumin excretion. Interestingly, imidapril improved asymptomatic dysphagia in patients with a history of stroke. In the same patients it increased serum substance P levels, while the angiotensin II receptor antagonist losartan was ineffective. These studies indicate that imidapril is a versatile ACE inhibitor. In addition to its effectiveness in the treatment of hypertension, CHF, and AMI, imidapril has beneficial effects in the treatment of diabetic nephropathy and asymptomatic dysphagia. Good tissue penetration and inhibition of tissue ACE by imidapril contributes to its effectiveness in preventing cardiovascular complications of hypertension. The major advantages of imidapril are its activity in the treatment of various cardiovascular diseases and lower incidence of cough compared with some of the older ACE inhibitors.

Role of female sex hormones in the development and reversal of dahl hypertension

Female sex hormones protect against the development of Dahl hypertension mediated by increases in dietary sodium. The role of female sex hormones in the reversal of Dahl hypertension mediated by decreases in dietary sodium is unknown. The goal of this study was to identify sex differences in the reversal of Dahl hypertension and the associated changes in water and electrolyte homeostasis. Male (M, n=8), female (F, n=8), and ovariectomized female (OVX, n=9) Dahl salt-sensitive rats were instrumented with an abdominal radiotelemetry device for 24-hour monitoring of blood pressure (BP) and heart rate. Daily measurements of food intake, water intake, and urine output were recorded as diet was changed from a low-sodium diet (0.15% NaCl) to a diet containing 8% NaCl. The diet was then changed back to 0.15% NaCl. The responses to changes in the salt diet were compared with responses observed in rats (M, n=4; F, n=4; OVX, n=4) that were maintained on 0.15% NaCl during the experiment. Sex differences in BP were observed when M, F, and OVX rats were fed 8% NaCl diet for 2 weeks (152+/-4, 141+/-3, and 154+/-5 mm Hg, respectively). BP was significantly greater (P<0.05) in M and OVX rats than in F rats. Fluid balance (water intake minus urine volume) and sodium balance (sodium intake minus sodium excretion) were similar in all groups on the 8% NaCl diet. BP in time-control M, F, and OVX rats was 121+/-3, 130+/-4, and 162+/-11 mm Hg, respectively. Compared with time-control groups, differences in BP while rats were eating the 8% NaCl diet were observed in M and F rats but not OVX rats. Reinstatement of an NaCl-deficient diet reversed the hypertension in M and F but not OVX rats (124+/-4, 124+/-2, and 145+/-5 mm Hg, respectively). The changes in dietary sodium caused similar changes in renal handling of sodium and water in all groups of rats; therefore, the effect on blood pressure was independent of renal excretory function. The inability to reverse the hypertension by decreasing sodium intake in OVX rats and the development of spontaneous hypertension in OVX females maintained on a low-sodium diet indicates that removal of the female sex hormones predisposes the animal to the development of hypertension that is sodium independent. We conclude that female sex hormones protect Dahl S rats against the development of sodium-dependent and -independent hypertension.