In experimental models of hypertension, blood pressure reaches a higher level in male than in female rats. Because endothelin-1 (ET-1) seems to play a role in blood pressure elevation in deoxycorticosterone acetate (DOCA)-salt hypertension, we hypothesized that male DOCA-salt rats would display a greater vascular responsiveness to ET-1 than female DOCA-salt rats. Male and female Wistar rats were uninephrectomized, received DOCA injections (50 mg/kg/week) and water plus 1.0% NaC1/0.2% KC1. Control rats received vehicle and tap water. Responses to ET-1, norepinephrine (NE), serotonin (5-HT), IRL-1620, a selective endothelin-B- (ETB) receptor agonist, and acetylcholine (ACh) were evaluated in isolated aortic rings and also in vivo in the mesenteric microcirculation. Endotheliumintact aortas from male and female DOCA rats displayed increased sensitivity (p < 0.05) to NE and 5-HT, but decreased relaxation to ACh in comparison to aortas from respective control male and female rats. Endothelium-denuded, but not endothelium-intact, arteries from male DOCA rats displayed increased sensitivity (-log EC20) to ET-1, but no changes in ET-1 sensitivity were observed in female DOCA aortas. IRL-1620 induced contraction in male DOCa aortas, but not in female DOCA or control endothelium-denuded aortas. In the microcirculation, IRL-1620 induced vasodilation in male and female control rats, but marked vasoconstriction in male DOCA and minimal changes in vessels diameter in female DOCA rats. Bosentan, an ETA/ETB-receptor antagonist, induced a greater decrease in mean arterial blood pressure in male than in female DOCA-salt hypertensive rats. These data support the hypothesis that DOCA-salt rats exhibit gender differences in ET-1 vascular reactivity, which probably result from functional changes in ETB-receptors. The increased ETB responses in male DOCA-salt hypertensive rats may play a role in their higher blood pressure levels.
Address correspondence and reprint requests to Rita C.A. Tostes Passaglia, University of Sao Paulo - ICB I - Pharmacology Department, Av. Lineu Prestes, 1524 Sao Paulo, SP 05508-900 Brazil.
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