NG-nitro- l-arginine methyl ester-induced norepinephrine release from cardiac sympathetic nerve endings in anesthetized cats

Abstract

Using the cardiac dialysis technique in the anesthetized cat, we examined the effects of N G-nitro- l-arginine methyl ester ( l-NAME, a nitric oxide (NO) synthase inhibitor, 100 mM) on sympathetic modulation. Local administration of l-NAME induced increases in dialysate norepinephrine (NE) levels, which were not affected by the addition of ω-conotoxinGVIA. High-potassium (high K +)-evoked increases in dialysate NE levels were suppressed by addition of l-NAME. To confirm the involvement of NO in the NE releasing action, we compared dialysate NE levels during the administration of l-NAME or d-NAME and no significant differences between them. l-NAME induces spontaneous non-exocytotic NE release but suppresses exocytotic NE release by high K +. l-NAME may interact with both NE transport and NE release mechanisms. However, NO may contribute little to the amounts of NE released by l-NAME.