DISTRIBUTION AND FUNCTION OF NITRIC OXIDE-CONTAINING NERVES IN CANINECORPUS CAVERNOSUM AND SPONGIOSUM

Specimens of penile erectile tissue from the corpus cavernosum (CC) an d corpus spongiosum (CS) of beagle dogs were investigated with referen ce to morphological and functional aspects of the nitric oxide (NO) sy stem. Using immunohistochemistry, the smooth muscle bundles of the CC were found to contain a rich innervation, as seen by the pan-neuronal marker, protein gene product 9.5. A large number of nerves also staine d positively for acetylcholine esterase. There was a moderate to rich supply of nerves containing NO synthase, which was frequently co-local ized with vasoactive intestinal polypeptide. CS preparations from the proximal penis (the spongious bulb) had an innervation similar to that of the CC. However, CS preparations from the distal penis had a disti nctly lower density of nerves than the proximal part, and spongious ti ssue from the glans penis was practically devoid of nerves. In isolate d preparations of proximal and distal CC and CS, contracted by noradre naline, electrical field stimulation (EFS) produced frequency-dependen t relaxations. The responses were less pronounced in preparations from the distal penis, particularly in the CS. Pre-treatment with the NO-s ynthesis inhibitor N-G-nitro-L-arginine abolished all relaxations. Car bachol effectively relaxed noradrenaline-contracted strips. The respon ses were similar in proximal preparations from the CC and CS, and sign ificantly less pronounced in strips from the distal penis. N-G-nitro-L -arginine significantly reduced the relaxant effect of carbachol. Prep arations of spongious tissue from the glans penis did not react to hig h potassium solution, addition of noradrenaline, or EFS. The results d emonstrate regional differences within the CS, both in innervation and functional responses.