Role of central and sympathetic nervous systems in pressor effect of L-NAME

The pressor effect of N -nitric-l-arginine methyl ester (l-NAME) in rats has been attributed to the inhibition of the endothelial nitric oxide synthase; however, recent findings suggest that the central and sympathetic nervous systems may be also involved. In the present work, the authors attempted to study the possible central and sympathetic mechanisms involved in the pressor effect of l-NAME. They compared mean arterial pressure response during 1 h of continuous infusion of normal saline or l-NAME (0.031 mg. kg. min ) in Wistar rats treated with reserpine, adrenal medullectomy, pithing, and pithing + medullectomy. After 15-20 min infusion, a significantly greater increase of mean arterial pressure was observed in anesthetized rats with l-NAME and l-NAME + medullectomy versus rats with l-NAME + reserpine and l-NAME + pithing, and the magnitude of the difference increased further during the continuous 1-h l-NAME infusion. Adrenal medullectomy totally abolished the pressor effect of l-NAME in pithed group. The present findings suggest that the central and sympathetic nervous systems play important roles in the maintenance of the pressor effect of l-NAME, while the adrenal medulla becomes important only when the sympathetic nervous system has been suppressed.