Peptidergic innervation of the porcine oviduct studied by double-labelling immunohistochemistry.

Neurochemical coding of nerve fibres supplying the porcine oviduct was studied by means of double-labelling immunofluorescence. Immunoreactivities to rate-limiting enzymes of catecholamine synthesis, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DbetaH), were found in numerous oviductal nerve fibres. All TH-immunoreactive (TH-IR) nerve processes were simultaneously DbetaH-IR. This subset of nerves was considered to be sympathetic noradrenergic. In addition to noradrenaline, many axons additionally exhibited immunoreactivity to neuropeptide Y (NPY), or leu5-enkephalin (Leu-ENK). Small numbers of somatostatin- (SOM-) or vasoactive intestinal polypeptide-immunoreactive (VIP-IR) fibres, sometimes coexpressing TH/DbetaH-immunoreactivity, supplied the porcine oviduct. Substance P- (SP- ) and/or calcitonin gene-related peptide-immunoreactive (CGRP-IR) nerve fibres were only sporadically found. Although these nerves did not contain TH/DbetaH-immunoreactivity, they often ran in close vicinity to TH/DbetaH-IR axons, forming together thin nerve bundles. All the above mentioned subpopulations of nerve fibres were found throughout the entire length of the oviduct being mainly related to the vascular and non-vascular smooth myocytes. However, some of the putative afferent (i.e. SP- or CGRP-IR) or parasympathetic efferent (i.e. VIP- or NPY-IR but TH/DbetaH-immunonegative) axons were located beneath the epithelium. Such distribution implies these nerve fibres to be involved in the regulation of the oviductal blood flow, non-vascular smooth myocyte tonus, transmission of sensory information and control of the epithelial secretion.