THE BASAL ENDOTHELIAL INHIBITORY INFLUENCE ON VASCULAR TONE IS NOT AFFECTED IN NITROGLYCERIN-TOLERANT RAT AORTA

Prolonged exposure to nitrovasodilators produces tolerance and depende nce. Nitrovasodilators exert their action on vascular smooth muscle ce lls by activation of guanylyl cyclase. Nitrates share this mechanism w ith endothelial NO, which exerts a continuous inhibitory influence on vascular tone. Whether the basal inhibitory endothelial influence migh t be affected in rat aorta exposed in vitro to a tolerance-inducing co ncentration of nitroglycerin was investigated in this study. It was fo und that the basal inhibitory influence, assessed as its inhibitory in fluence on norepinephrine-induced contraction, and as the contractile effect of N-nitro-L-arginine methyl ester or methylene blue, was the s ame in nitroglycerin-tolerant and control aortic rings. Our results gi ve an indication that changes in basal inhibitory endothelial influenc e are not involved in the phenomena of nitrate tolerance and nitrate d ependence.