NITRIC-OXIDE INHIBITS CONTRACTION OF ISOLATED PIG URETERAL SMOOTH-MUSCLE

Purpose: To investigate the L-arginine/nitric oxide (NO) pathway in th e pig isolated ureter. Materials and Methods: Functional inhibitory ef fects mediated by NO were assessed and correlated with cyclic nucleoti de levels. Nitric oxide synthase (NOS) activity was measured by monito ring the conversion of [H-3]-arginine to [H-3]-citrulline. Immunohisto chemical studies were performed. Results: The NO-donor SIN-1 reduced i n a concentration-dependent manner the frequency of contractions, wher eas NO completely interrupted the contractile activity. In precontract ed strips exposed to SIN-1 or NO, there were 6- and 12-fold increases of the cyclic GMP levels in comparison with control preparations. Acti vity of NOS was moderate. Overall innervation of the ureter was sparse , and there were few NOS-immunoreactive nerves. Conclusion: Although f ew NOS-containing nerves were found, pathways regulating the cyclic GM P levels of pig ureteral smooth muscle were demonstrated. Such pathway s may be important targets for drugs producing relaxation of the mamma lian ureter.