LOCALIZATION OF REGULATORY PEPTIDES IN THE MALE UROGENITAL APPARATUS OF DOMESTIC EQUIDAE - A COMPARATIVE IMMUNOHISTOCHEMICAL STUDY IN EQUUS-CABALLUS AND EQUUS-ASINUS

An immunohistochemical study was carried out on specimens of testis, e xcurrent duct including the male accessory glands and urethra in its v arious tracts in the horse and the donkey, in order to localize nine r egulatory peptides. Immunoreactivities were tested by means of Labelle d Strept Avidin-Biotin (LSAB) method. The study has shown that Equine male genitalia are supplied by many peptide immunoreactive nerves cont aining NPY-, VIP-, leu- and met-Enkephalin-, Substance P-, CGRP- and B ombesin/GRP-like peptides, each of them having a characteristic distri bution 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-like- immunoreactive endocrine cells were shown in the bulbourethral gland o f the horse. In both species it was evident that an extensive utilizat ion of NPY and VIP exists. A contingent of NPY- and VIP-ir nerve fiber s may have an intrinsic origin. The other regulatory peptides tested s how a characteristic distribution pattern, limited to some organs and peculiar to each of the two species of Equidae. Differences observed c omparing E. caballus and E. asinus might be related to the species-spe cific balance of the accessory neurotransmitters which in turn accompa ny adrenergic innervation. In both species it is noteworthy the comple te absence of any regulatory peptide in the testis, with the exception of the perivascular localization of NPY-ir nerve fibers.