NADPH-diaphorase and NANC relaxations are correlated in the sheep urinary tract

The present investigation was performed with the purpose of revealing by histochemical examination of NADPH-diaphorase activity and electrical field stimulation (EFS) of isolated preparations in vitro, whether a nitrergic innervation is present in the lower urinary tract of the sheep. NADPH-diaphorase positive fibers were found in the trigone and urethra, but not in detrusor and ureter. EFS elicited L-nitroarginine-sensitive relaxations of precontracted preparations from the trigone and urethra while it did not relax detrusor and ureteral preparations. The present results show a direct regional correlation between the NADPH-diaphorase activity and EFS-induced relaxations, and suggest the presence of an inhibitory nitrergic innervation, which might be of importance for relaxation of the bladder neck and urethra during voiding.