Effect of chronic ETA‐selective endothelin receptor antagonism on blood pressure in experimental and genetic hypertension in rats

Abstract

Chronic treatment with a combined ET_A/ET_B endothelin receptor antagonist has been shown to reduce blood pressure in experimental rat models of hypertension in which endothelin‐1 gene overexpression occurs in the walls of blood vessels, particularly small, resistance‐sized arteries, but not in those genetic or experimental models of hypertension in which there is no overexpression of vascular endothelin‐1. Failure of some experimental models of hypertension to respond to treatment with the combined ET_A/ET_B endothelin antagonist may be due in part to blockade of vasorelaxant endothelial ET_B receptors which could in theory reduce the efficacy of endothelin antagonism. In this study the orally active ET_A‐selective endothelin antagonists A‐127722.5 and LU 135252 were used in chronic experiments on deoxycorticosterone acetate (DOCA)‐salt hypertensive rats (which overexpress vascular endothelin‐1 and respond with blood pressure lowering to combined ET_A/ET_B endothelin receptor antagonism), on spontaneously hypertensive rats (SHR) (which do not overexpress vascular endothelin‐1 and do not respond with blood pressure lowering to the combined ET_A/ET_B receptor antagonist), and in 1‐kidney 1 clip Goldblatt (1‐K 1C) hypertensive rats (which present mild overexpression of vascular endothelin‐1 but do not respond with blood pressure lowering to the combined ET_A/ET_B receptor antagonist). Additionally, it has been suggested that interruption of the renin‐angiotensin system may sensitize responses to endothelin antagonism. Accordingly, SHR were treated with an angiotensin converting enzyme inhibitor, cilazapril, in addition to the ET_A receptor antagonist. Blood pressure of DOCA‐salt hypertensive rats was lowered by a mean of 24 and of 27 mmHg (P−1 day⁻¹), and by 18 mmHg by LU 135252 50 mg kg⁻¹ day⁻¹. SHR treated with A‐127722.5 for 8 weeks starting at 12 weeks of age exhibited the same progressive rise in blood pressure as untreated SHR. Addition of cilazapril resulted in similar reduction of blood pressure in A‐127722.5‐treated and untreated SHR. Treatment of 1‐K 1C hypertensive rats with the dose of LU 135252 which lowered blood pressure in DOCA‐salt hypertensive rats did not cause any reduction in blood pressure relative to untreated rats. These results demonstrate that treatment with either dose of the selective ET_A receptor antagonists A‐127722.5 or LU 135252 caused reductions in blood pressure similar to those obtained for a combined ET_A/ET_B endothelin antagonist. Blood pressure was lowered only in hypertensive rats known to overexpress vascular endothelin‐1 (DOCA‐salt hypertensive rats) but not in those which do not (SHR) or only have mild vascular overexpression of endothelin‐1 gene (1‐K 1C hypertensive rats). Reduction in activity of the renin‐angiotensin system in SHR did not sensitize blood pressure to potential hypotensive effects of an ET_A‐selective receptor antagonist.