URETHRAL RELAXATION AFTER ELECTROSTIMULATION IN THE GUINEA-PIG IS INDEPENDENT OF NITRIC-OXIDE

Purpose: To investigate whether the relaxation of the striated urethra l sphincter in guinea pigs is mediated by nitric oxide. Materials and Methods: After sacrifice, urethral rings were cut between the bladder neck and the penile crura and mounted in an in vitro bath. Maximal iso metric tension obtained at 1, 3, 10 and 25 Hz electrical stimulation ( Tmax) for 5 to 30 sec was measured. Results: Tmax at 25 Hz was not cha nged by pretreatment with 10(-4)M nitroprusside or 10(-4)M N-G-nitro-L -arginine. In urethral tissue precontracted with 10(-4)M noradrenaline , a significant relaxation of 16-25% was found at 10 Hz. This relaxati on could not be prevented by pretreatment with 10(-4)M N-G-nitro-L-arg inine and was not enhanced by the presence of 10(-3)M L-arginine. Conc lusion: Noradrenaline-precontracted urethral rings of male guinea pigs exhibit a maximal relaxation at 10 Hz, which does not depend on nitri c oxide.