[Peptide innervation of the penis]

Immunoreactive (IR) vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY) nerve fibers processes have been observed in venous and arterial tunicae and in intracavernous smooth muscles of the human penis taken at autopsy or during surgery using light and electron microscopic immunohistochemical techniques. Numerous IR-VIP and IR-NPY nerve fibers were mostly concentrated in the inner part of the adventitia close to the media of the arterial and venous vessels. In the corpora cavernosa and in the corpus spongiosum, IR-VIP and IR-NPY nerve processes were intermingled between the smooth muscle fibers around the sinusoid spaces. The density of the staining was much more important for NPY than for VIP. Positive soma were not observed in the penis. At ultrastructural level, post embedding immunogold technique, IR-VIP and IR-NPY were localized exclusively in large dense granules of nerve terminals. This peculiar distribution of IR-VIP and IR-NPY nerve fibers suggested that it could participate in regulating arterial and venous blood flow and intracavernous smooth muscle tone in the mechanism of flaccidity and erection of the penis.