EFFECTS OF CHRONIC NO SYNTHASE INHIBITION IN RATS ON RENIN-ANGIOTENSIN SYSTEM AND SYMPATHETIC NERVOUS-SYSTEM

This study was designed to assess the role of renin and of the sympath oadrenal system in the maintenance of the hypertension induced by chro nic nitric oxide synthase (NOS) inhibition in rats kept on a normal (R S) or a low-sodium (LS) diet. With the administration of N-G-nitro-L-a rginine methyl ester (L-NAME) in drinking water (0.4 g/l) for 6 wk, me an intra-arterial blood pressure rose to a similar extent to 201 mmHg in the RS and 184 mmHg in the LS animals. Simultaneously, plasma norep inephrine was increased to 838 and 527 pg/ml and epinephrine to 2,041 and 1,341 pg/ml in RS and LS, respectively. Plasma neuropeptide Y leve ls did not change. Plasma renin activity rose to 21 ng . ml(-1). h(-1) in RS but remained at 44 ng . ml(-1). h(-1) in the LS. Both losartan (10 mg/kg) and phentolamine (0.1 mg/kg) intravenous bolus injections r educed blood pressure considerably in the L-NAME hypertensive animals. Whole brain NOS activity was reduced by 84%. Hypertension induced by chronic NOS inhibition in LS as well as in RS fed rats seems to be sus tained by an interaction of several mechanisms, including the activati on of the sympathetic nervous system and the renin-angiotensin system.