NITRIC-OXIDE IS NOT INVOLVED IN THE EFFECTS INDUCED BY NONADRENERGIC NONCHOLINERGIC STIMULATION AND CALCITONIN-GENE-RELATED PEPTIDE IN THE RAT MESENTERIC VASCULAR BED

The mechanism involved in the effects induced by the activation of per ineural non-adrenergic non-cholinergic (NANC) nerves or by exogenous c alcitonin gene-related peptide (CGRP) was investigated in the rat mese nteric vascular bed (MVB) perfused with Kreb's solution containing met hoxamine and guanethidine. The activation of NANC terminals of the tis sue was carried out by means of electrical field stimulation (EFS). An increase in the perfusion pressure of the preparations was observed i n the presence of two inhibitors of nitric oxide synthase: N(G)-monome thyl-L-arginine (L-NMMA) (100 muM) and N(G)-nitro-L-arginine methyl es ter (L-NAME) (100 muM). However L-NMMA and L-NAME did not modify the r elaxant effect induced by EFS and exogenous CGRP. Furthermore the rela xant effect induced by EFS and exogenous CGRP was not affected by the removal of endothelium from the preparations. These results provide ev idence that the vasodilation induced by NANC stimulation or by exogeno us CGRP in MVB does not involve NO production.