Antihypertensive mechanisms of chronic captopril or N-acetylcysteine treatment in L-NAME hypertensive rats

Abstract

Hypertension due to chronic inhibition of NO synthase (NOS) by Nω-nitro-L-arginine methyl ester (L-NAME) administration is characterized by both impaired NO-dependent vasodilation and enhanced sympathetic vasoconstriction. The aim of our study was to evaluate changes in the participation of major vasoactive systems in L-NAME-treated rats which were subjected to simultaneous antihypertensive (captopril) or antioxidant (N-acetylcysteine, NAC) treatment. Three-month-old Wistar males treated with L-NAME (60 mg/kg/ day) for 5 weeks were compared to rats in which L-NAME treatment was combined with simultaneous chronic administration of captopril or NAC. Basel blood pressure (BP) and its acute responses to consecutive i.v. injections of captopril (10 mg/kg), pentolinium (5 mg/kg), L-NAME (30 mg/ kg), tetraethylammonium (TEA, 16 mg/kg) and nitroprusside (NP, 20 μg/ kg) were determined in conscious rats at the end of the study. The development of L-NAME hypertension was prevented by captopril treatment, whereas NAC treatment caused only a moderate BP reduction. Captopril treatment normalized the sympathetic BP component and significantly reduced residual BP (measured at full NP-induced vasodilation). In contrast, chronic NAC treatment did not modify the sympathetic BP component or residual BP, but significantly enhanced NO-dependent vasodilation. Neither captopril nor NAC treatment influenced the compensatory increase of TEA-sensitive vasodilation mediated by endothelium-derived hyperpolarizing factor in L-NAME-treated rats. Chronic captopril treatment prevented L-NAME hypertension by lowering of sympathetic tone, whereas chronic NAC treatment attenuated L-NAME hypertension by reduction in the vasodilator deficit due to enhanced NO-dependent vasodilation.