Correlation of Neuronal Nitric Oxide Synthase with Penile Erection in Diabetic Rats

Moon, Ki Hak; Jung, Hee Chang; Park, Tong Choon; Lee, Yung Chang; Huh, Khun; Park, Jong Min; Suh, Jun Kyu

Abstract

Diabetes mellitus (DM) is an important cause of organic impotence in man. The exact pathogenesis remains debatable although it has been focused on cavernosal neuropathy and/or endothelial dysfunction. This study was designed to investigate the effect of DM on penile erection, especially in association with nitric oxide synthase (NOS) in corpus cavernosum of diabetic rats. NOS studies of rat penis were performed in diabetic (DM was induced for 3, 6, 9, 12 weeks, respectively, by intraperitoneal administration of streptozotocin, 60mg/kg), in control and neurotomy group (3 weeks after bilateral cavernous nerve transection). The experiments consisted of nicotinamide dinucleotide phosphate (NADPH) diaphorase activity with spectrophotometric assay for NOS catalytic activity, NADPH diaphorase staining for the identification of NOS containing nerve fibers, and Western blotting analysis with anti-brain NOS antibody for the expression of neuronal NOS. Finally, these results were compared with erectile response to cavernous nerve stimulation in diabetic and in control rats. In assay of NADPH diaphorase activity, NOS activity decreased significantly in penis of diabetic rat as compared to that of controls. Between the diabetic groups, NOS activity was not seen significantly different, and in neurotomy groups it was similar to that of diabetic groups. On histochemical staining of penile tissues, the number of NADPH-positive nerve fibers in control group (a mean of 127+/-6 fibers recorded in 4 random fields on each corporal side) contrasted significantly with that of the bilateral cavernous nerve ablation group (a mean of 12+/-2). In diabetic group, the number of NOS-containing nerve fibers was gradually reduced along with duration of diabetes (from 92+/- 3 at 3 weeks to 28+/-3 at 12 weeks). In addition, analysis of blot density of neuronal NOS by Western blotting showed similar findings: 16% at 3 weeks and 8% at 12 weeks in diabetic group, 5% in neurotomy group and 27% in controls, based on the density of the rat cerebellum. Furthermore, erection response to cavernous nerve stimulation was also decreased in diabetic rats along with DM duration. The results, indicated that reduction of cavernous NOS, particularly, its neuronal form at the level of NO production plays an important role on the pathogenesis of erectile impotence in diabetic rats although the role of endothelial N0S in DM remains to be elucidated. Furthermore, cavernosal NADPH diaphorase staining and/or NOS activity may allow to characterize certain pathological condition, which comprise neurogenic impotence.