Blood pressure in conscious and anesthetized adrenal-enucleated Sprague-Dawley and Wistar-Furth rats

Changes in renal hemodynamics and excretory function induced by a reduction of ANG II effects during renal development

The aim was to evaluate whether blockade of ANG II effects during renal development modifies the renal response to an increment of plasma amino acid concentration. It was also examined in anesthetized rats whether the reduction of the renal ability to eliminate an acute volume expansion (VE), elicited by blockade of ANG II during renal development, is sex and/or age dependent. Newborn Sprague-Dawley rats were treated with vehicle or an AT(1)-receptor antagonist (ARA) during postnatal nephrogenesis. Amino acid infusion induced increments (P < 0.05) of glomerular filtration rate (31 +/- 6%) and renal plasma flow (26 +/- 5%) in male but not in female vehicle-treated rats. Natriuretic and diuretic responses to amino acid infusion were similar in male and female vehicle-treated rats. These renal hemodynamics and excretory responses to amino acid infusion were abolished in ARA-treated rats. Renal responses to VE were evaluated at 3-4 and 9-10 mo of age in vehicle and ARA-treated rats. VE-induced natriuresis and diuresis were reduced by more than 38% (P < 0.05) in 3- to 4-mo-old male and female ARA-treated rats. An age-dependent reduction (P < 0.05) in the renal ability to eliminate VE was found in male but not in female rats treated with ARA. Our results demonstrate that the renal effects induced by an increment in amino acids are abolished when ANG II effects have been reduced during nephrogenesis. In addition, this reduction of ANG II effects elicits an impairment of the renal ability to eliminate an acute VE in males and females, which is aggravated by age only in male rats.

Sex differences in renal injury and nitric oxide production in renal wrap hypertension

To investigate the faster rate of renal disease progression in men compared with women, we addressed the following questions in the renal wrap (RW) model of hypertension: 1) Do sex differences exist in RW-induced renal injury, which are independent of sex differences in blood pressure? 2) Do sex differences in nitric oxide (NO) production exist in RW hypertension? Male (M) and female (F) rats underwent sham-operated (M-Sham, n = 7; F-Sham, n = 10) or RW (M-RW, n = 13; F-RW, n = 14) surgery for 9 wk. Markers of renal injury, including the glomerulosclerosis index (F-RW, 0.70 +/- 0.1 vs. M-RW, 2.2 +/- 0.6; P < 0.05), mean glomerular volume (F-RW, 1.05 +/- 0.050 x 10(6) vs. M-RW, 1.78 +/- 0.15 x 10(6) microm(3); P < 0.001), and proteinuria (F-RW, 68.7 +/- 15 vs. M-RW, 124 +/- 7.7 mg/day; P < 0.001) were greater in RW males compared with RW females. Endothelial NO synthase protein expression was elevated in the renal cortex (3.2-fold) and medulla (2.2-fold) 9 wk after RW in males, whereas no differences were observed in females. Neuronal NO synthase protein expression was unchanged in the renal cortex in males and in both the renal cortex and medulla in females, whereas in the male medulla, neuronal NOS was decreased by 57%. These data suggest the degree of renal injury is greater in male compared with female rats in RW hypertension despite similar degrees of hypertension and renal function and may involve sex differences in renal NO metabolism.

Resistance to mineralocorticoid-induced hypertensive vascular disease

To support our contention that the Wistar-Furth rat is resistant to mineralocorticoid hypertension, we assessed the effects of deoxycorticosterone (DOC) administration or renal artery stenosis on the development of hypertension in the Sprague-Dawley and Wistar-Furth rat strains. Weekly administration of mineralocorticoid in the form of DOC pivalate resulted in rapid, severe hypertensive cardiovascular disease in Sprague-Dawley rats. Within 5 weeks the mean conscious systolic blood pressures in steroid-treated and control rats were 186 +/- 4 and 118 +/- 5 mm Hg, respectively. In contrast, blood pressures of Wistar-Furth rats were only moderately elevated, even after 10 weeks of DOC pivalate administration (136 +/- 2 vs 116 +/- 2 mm Hg for controls). Furthermore, none of the steroid-treated Wistar-Furth animals exhibited cardiovascular lesions. In parallel studies, littermates of these rat strains were subjected to renal artery stenosis and blood pressures were determined weekly in conscious rats. Silver clip constriction of the left renal artery, in the presence of the contralateral kidney, resulted in a rapid, sustained elevation of blood pressure in both Sprague-Dawley and Wistar-Furth rat strains (177 +/- 4 and 176 +/- 5 mm Hg, respectively). Corticosteroid levels were also determined in DOC-treated Sprague-Dawley and Wistar-Furth rats. The regimen employed resulted in a 10-fold increase in DOC levels as compared with controls, and the levels achieved were comparable in both strains. Thus, the Wistar-Furth rat appears to be selectively resistant to mineralocorticoid hypertensive vascular disease and thus affords a model for studying mechanisms of steroid hypertension.