Diabetes mellitus increases nitric oxide synthase in penises but not in major pelvic ganglia of rats.

Abstract

To determine the effect of diabetes mellitus (DM) on erectile function and evaluate the levels of nitric oxide synthetase (NOS) activity in streptozotocin-induced diabetic rats. Rats were studied at 9 weeks and 14 weeks after the induction of DM by streptozotocin and compared with untreated control rats. Erectile potency was assessed physiologically by testing and recording mating behaviour. NOS activity was assayed in penile tissues and major pelvic ganglia (MPG) by conversion of [3H] L-arginine to [3H] citrulline. Histological, ultrastructural and immunohistochemical studies of penile tissues were performed in similar groups of rats. Diabetes mellitus adversely and significantly degraded all parameters of mating behaviour, thus indicating defective erectile potency. However, NOS activities in penile tissues from both groups of diabetic rats were significantly higher than those in controls (P < 0.01). In MPG, NOS activities were not significantly different between diabetic and control rats (P > 0.05). Histological, ultrastructural and immunohistochemical studies of penile tissues revealed no significant differences between control and diabetic rats, indicating an intact effector organ (smooth muscles) in rats with up to 14 weeks of DM. The impotence frequently observed in diabetic subjects would suggest that despite the increase in NOS activity in the penis, the pharmacological action of nitric oxide is impaired.