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(Hypertension. 1995;26:236-243.)
© 1995 American Heart Association, Inc.

Articles

Nitric Oxide and Prostaglandins in the Prolonged Effects of Losartan and Ramipril in Hypertension

Victoria Cachofeiro; Rosaura Maeso; Elena Rodrigo; Josefa Navarro; Luis M. Ruilope; Vicente Lahera

From the Department of Physiology, Complutense University, Medical School, Madrid, Spain.

Correspondence to V. Cachofeiro, Departamento de Fisiología, Facultad de Medicina, Universidad Complutense, Madrid 28040, Spain.

Abstract We investigated the role of endogenous nitric oxide, kinins, and prostaglandins in the vasodepressor and renal excretory effects of the angiotensin II receptor antagonist losartan and the angiotensin-converting enzyme inhibitor ramipril administered for 1 week to spontaneously hypertensive rats. To this end, either losartan (10 mg/kg per day) or ramipril (2.5 mg/kg per day) was administered in drinking water with or without simultaneous administration of (1) the nitric oxide synthesis inhibitor N^G-nitro-L-arginine methyl ester (L-NAME, 6 mg/kg per day), (2) the cyclooxygenase inhibitor indomethacin (5 mg/kg per day), (3) the bradykinin B₂ receptor antagonist Hoe 140 (0.5 mg/kg per day SC), or (4) L-NAME plus indomethacin. Both losartan and ramipril significantly reduced blood pressure as measured by the tail-cuff method. L-NAME increased blood pressure when administered solely or in combination with losartan. However, L-NAME attenuated the hypotensive effect of ramipril. Indomethacin did not affect blood pressure but it reduced the antihypertensive action of losartan and ramipril. Indomethacin administration did not potentiate the increase in blood pressure induced by L-NAME. However, the concurrent administration of both inhibitors almost totally blunted the vasodepressor action of ramipril. By contrast, losartan administration in the presence of L-NAME and indomethacin increased blood pressure to a level similar to that after losartan plus L-NAME. Hoe 140 did not modify either blood pressure or the hypotensive effects of losartan or ramipril. Increases in diuresis and water intake were observed during ramipril administration. Both effects were blunted only with the concurrent administration of L-NAME and indomethacin. None of the cotreatments were able to modify renal excretory function by themselves. These data suggest a contribution of endogenous nitric oxide and prostaglandins but not of kinins in the prolonged antihypertensive effect of both losartan and ramipril in the spontaneously hypertensive rat.

Key Words: nitric oxide • prostaglandins • kinins • angiotensin receptors • angiotensin-converting enzyme inhibitors • blood pressure • kidney function

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