Alterations in the nitric oxide synthase binding sites and non-adrenergic,non-cholinergic mediated smooth muscle relaxation in the diabetic rabbit bladder outlet: Possible relevance to the pathogenesis of diabetic cystopathy

Purpose: To investigate the effect of diabetes mellitus (DM) on the density and distribution of nitric oxide synthase (NOS) and the smooth muscle resp onses to non-adrenergic, non-cholinergic (NANC) nerve stimulation and exoge nous nitric oxide (NO) in the rabbit lower urinary tract. Materials and Methods: Transverse sections of detrusor, bladder neck and ur ethra, fr om control and six months alloxan-induced DM New Zealand White ra bbits were incubated with a radioligand for NOS ([H-3]-L-N-G-nitroarginine) . Densitometric analysis was performed on the autoradiographs, NADPH diapho rase histochemistry was also used as a marker for NOS activity. Responses t o NANC nerve stimulation (5 to 20 Hz) and to NO (10(-6) to 3 x 10(-4) M.) o n smooth muscle strips from detrusor, bladder neck and urethra were measure d in organ baths. Results: NOS binding sites were significantly (p <0.03) more dense in the b ladder neck than in the detrusor in both DM and control, groups. In DM blad der neck, NOS binding sites were significantly (p <0.04) increased compared with the controls. NADPH diaphorase activity appeared markedly increased i n the detrusor, bladder neck and urethra of DM animals compared with contro ls. The mean IC50 for exogenous NO in control versus DM were not statistica lly different in the bladder neck (1.03 x 10(-4) M versus 9.8 x 10(-5) M) a nd urethra (8.1 x 10(-5) M versus 8.8 x 10(-5) M), but the relaxations to 5 x 10(-6) M of NO were significantly impaired (p <0.04) in the DM urethral smooth muscle. NANC nerve-mediated relaxations were significantly impaired (p <0.001) in the DM urethral smooth muscle. Conclusions: Alterations of both the NOS binding sites and functional respo nses to NANC nerve stimulation suggest that NO may have a pathophysiologica l role in the urinary bladder dysfunction associated with DM.