Kinins, nitric oxide, and the hypotensive effect of captopril and ramiprilat in hypertension.

We investigated the role of kinins in the acute depressor effect of captopril and ramiprilat in spontaneously hypertensive rats. Since the vasodepressor action of kinins may be linked to the generation of prostaglandins and endothelium-derived relaxing factors, we also investigated the role of prostaglandins and nitric oxide in the blood pressure reduction caused by angiotensin converting enzyme inhibitors. To this end, we contrasted the hypotensive effects of captopril (10 mg/kg i.v.), ramiprilat (2 mg/kg i.v.), and the angiotensin II antagonist DuP 753 (30 mg/kg i.v.) in spontaneously hypertensive rats with and without pretreatment with a kinin antagonist (D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Phe-Thi-Arg-trifluoroacetic acid) (200 micrograms/kg/min i.v.), an inhibitor of nitric oxide synthesis (NG-monomethyl-L-arginine) (15 mg/kg + 10 mg/kg/hr i.v.), or an inhibitor of prostaglandin synthesis (indomethacin) (10 mg/kg i.v.). The kinin antagonist did not affect blood pressure in spontaneously hypertensive rats but did attenuate the hypotensive effect of captopril and ramiprilat; the kinin antagonist did not minimize the depressor action of DuP 753. The nitric oxide synthesis inhibitor increased blood pressure in spontaneously hypertensive rats and attenuated the hypotensive effect of captopril, ramiprilat, and DuP 753, but it did not impede the hypotensive effect of sodium nitroprusside. Pretreatment of hypertensive rats with indomethacin did not modify the acute hypotensive effect of ramiprilat or captopril. These data suggest a contribution of endogenous kinins and nitric oxide to the acute antihypertensive effect of captopril and ramiprilat in spontaneously hypertensive rats and of nitric oxide to the hypotensive effect of DuP 753.