Nitric Oxide Inhibits Contraction of Isolated Pig Ureteral Smooth Muscle

AbstractPurpose: To investigate the L-arginine/nitric oxide (NO) pathway in the pig isolated ureter.Materials and Methods: Functional inhibitory effects mediated by NO were assessed and correlated with cyclic nucleotide levels. Nitric oxide synthase (NOS) activity was measured by monitoring the conversion of [sup 3 H]-arginine to [sup 3 H]-citrulline. Immunohistochemical studies were performed.Results: The NO-donor SIN-1 reduced in a concentration-dependent manner the frequency of contractions, whereas NO completely interrupted the contractile activity. In precontracted strips exposed to SIN-1 or NO, there were 6- and 12-fold increases of the cyclic GMP levels in comparison with control preparations. Activity of NOS was moderate. Overall innervation of the ureter was sparse, and there were few NOS-immunoreactive nerves.Conclusion: Although few NOS-containing nerves were found, pathways regulating the cyclic GMP levels of pig ureteral smooth muscle were demonstrated. Such pathways may be important targets ...