Influence of denervation on neurogenic inhibitory response of corpus cavernosum and nitric oxide synthase histochemistry

Aims of this study were to functionally and histologically determine the localization of ganglia that distribute inhibitory nerves to the penile corpus cavernosum in dogs. In isolated corpus cavernosa from seven control dogs contracted with endothelin-l, transmural electrical stimulation (5 Hz for 40 s) elicited contractions which were reversed to relaxations by prazosin. The relaxation was abolished by NG-nitro-L-arginine (L-NNA), a nitric oxide (NO) synthase inhibitor, and restored by L-arginine. Parts of bilateral pelvic nerve plexuses running to the penis were surgically denervated in anesthetized three dogs, or the bilateral neuronal tissues close to the corpus cavernosum were removed for denervation in Seven dogs. One week after the operation, the dogs were sacrificed. Denervation of pelvic plexus did not attenuate neurogenic relaxations, whereas denervation of the distal portion abolished the responses. In the tissues close to the corpus cavernosum excised for denervation, ganglia containing abundant nerve cells and fibers stained by nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase method were histochemically detected. One week after the denervation, there were nb NADPH diaphorase-positive nerve fibers in the trabecula of corpus cavernosum. It is concluded that neurogenic relaxations of canine corpus cavernosum are mediated by NO synthesized from L-arginine in nerve terminals, and this nerve is originated from ganglia located close to the corpus cavernosum but not directly from the pelvic nerve plexus. (C) 1999 Elsevier Science B.V. All rights reserved.