A POSSIBLE ROLE FOR NITRIC-OXIDE (NO) AS A NEUROTRANSMITTER IN THE REGULATION OF URETERAL SMOOTH-MUSCLE TONE

The aim of the present study was to examine a possible role of nitric oxide (NO) in ureteral relaxation. Human ureteral rings were mounted i n organ bath chambers and precontracted with 80 mM KCl, then increasin g doses of the NO-donor SIN 1 were added to the bath chambers with and without blockade of the NO-pathway by methylen blue and protein kinas e inhibitors Rp-8-pCPT-cGMPS and Rp-8-CPT-cAMPS. Another study was con ducted with electrical field stimulation (EFS) to induce contraction a nd relaxation of the tissue after incubation with N-G-nitro-L-arginine (L-NORAG) and tetradotoxin (TTX). For detection of NO-synthase (NOS) containing nerve fibers tissue preparations were stained immunhistoche mically. Ureteral rings were dose dependently relaxed by SIN-1. Preinc ubation with methylene blue significantly reduced the relaxations indu ced by SIN-1. No effects of L-NORAG and TTX on EFS induced relaxations were found. Immunhistochemistry showed NO-synthase positive neuronal axons as well as nerve ending like structures in the muscular layers. Our results suggest a possible role of NO as a mediator of ureteral re laxation.