Localization of regulatory peptides in the male urogenital apparatus of domestic equidae: a comparative immunohistochemical study in Equus caballus and Equus asinus

Abstract

An immunohistochemical study was carried out on specimens of testis, excurrent duct including the male accessory glands and urethra in its various tracts in the horse and the donkey, in order to localize nine regulatory peptides. Immunoreactivities were tested by means of Labelled Strept Avidin-Biotin (LSAB) method. The study has shown that Equine male genitalia are supplied by many peptide immunoreactive nerves containing NPY-, VIP-, leu- and met-Enkephalin-, Substance P-, CGRP- and BombesinIGRP-like peptides, each of them having a characteristic distribution pattern. These neurotransmitters were localized in nerve fibers running in the connective tissue or in contact with the smooth muscle cells, as well as in sub- and intraepithelial nerve terminals, and in perivascular nerve fibers. In addition, leu- and met-Enkephalin-likeimmunoreactive endocrine cells were shown in the bulbourethral gland of the horse. In both species it was evident that an extensive utilization of NPY and VIP exists. A contingent of NPY- and VIP-ir nerve fibers may have an intrinsic origin. The other regulatory peptides tested show a characteristic distribution pattern, limited to some organs and peculiar to each of the two species of Equidae. Differences observed comparing E. caballus and E. asinus might be related to the speciesspecific balance of the accessory neurotransmitters which in turn accompany adrenergic innervation. In both species it is noteworthy the complete absence of any regulatory peptide in the testis, with the exception of the perivascular localization of NPY-ir neme fibers.