CAPSAICIN-INDUCED NITRIC-OXIDE-DEPENDENT RELAXATION IN ISOLATED DOG URETHRA

Capsaicin (5 x 10(-8) to 5 x 10(-5) M) produced a non-adrenergic and n on-cholinergic phasic relaxation in a concentration-dependent manner i n isolated dog urethral preparations precontracted by noradrenaline. T he mode of action of capsaicin was investigated with special reference to the possible involvement of endogenous nitric oxide (NO). A marked tachyphylaxis was observed in the responses to capsaicin. Pretreatmen t with N-G-nitro-L-arginine-methyl-ester (L-NAME) prevented or markedl y reduced the inhibitory effect of L-NAME. Methylene blue inhibited th e capsaicin-induced relaxation. In preparations stored at 4 degrees C for 72 h, the reduction in the capsaicin-induced relaxation was signif icantly greater than that in the relaxation induced by either electric al field stimulation or by sodium nitroprusside. We conclude that caps aicin produces an endogenous-NO-dependent relaxation in the isolated d og urethra via mechanisms that deteriorate during cold storage of the preparations. (C) 1997 Elsevier Science B.V.