The human penis: an unusual penetration of NPY-immunoreactive nerves within the medial muscle coat of the deep dorsal vein.

The deep dorsal penile vein was obtained from seven patients undergoing surgery for erectile dysfunction. The veins were studied histologically and immunohistochemically for serotonin, dopamine beta-hydroxylase, vasoactive intestinal polypeptide, neuropeptide Y, substance P, calcitonin gene-related peptide, somatostatin, and [Leu]- and [Met]enkephalin. Histologically, the deep dorsal vein was found to be a large muscular vein with a thin endothelial lining. The tunica media was composed of an inner longitudinally and an outer circularly arranged smooth muscle layer. Numerous vasa vasorum (up to 30 in a single transverse section) were found in the tunica adventitia. The greatest density of nerves supplying the deep dorsal vein and vasa vasorum were neuropeptide Y-immunoreactive nerves followed (in a decreasing order) by vasoactive intestinal polypeptide- and dopamine beta-hydroxylase-immunoreactive nerves. Substance P-, calcitonin gene-related peptide- and somatostatin-immunoreactive nerves, but not serotonin-, [Leu]- and [Met]enkephalin-immunoreactive nerves, were occasionally found around the deep dorsal vein. All these nerve fibers were confined to the adventitial-medial border except neuropeptide Y-immunoreactive nerves which in addition penetrated the tunica media to the subendothelial layer of the deep dorsal vein. In contrast, neuropeptide Y-immunoreactive nerves supplying the vasa vasorum were always confined to the adventitial-medial border. The possible function of the medial innervation of the deep dorsal vein by neuropeptide Y-immunoreactive nerves is discussed.