Nerves immunoreactive to vasoactive intestinal polypeptide in the porcine female genital tract

The immunoreactivity of vasoactive intestinal polypeptide (VIP) was localized at the light-microscopical level in cryostat sections using a peroxidase-antiperoxidase technique or at the electron-microscopical (EM) level in glutaraldehyde-fixed, resin-embedded sections, using an immunogold technique, of tissue samples from the genital tract of cycling pigs. X-ray micro-analysis of glutaraldehyde-dichromate-fixed sections was used to discriminate noradrenaline-containing nerves. VIP immunoreactivity was localized to nerves associated to some degree with epithelial cells, blood vessels and non-vascular smooth muscle. VIP nerves were most concentrated in the cervix and the uterus, localized in the submucosa, the muscle layers and the adventitia. Nerve profiles were also seen accompanying blood vessels in the endometrium, running close to the uterine glands. In the oviduct, VIP nerves had a similar localization though less dense. At the EM level, the immunogold localization confirmed the above-mentioned results, VIP being localized in synaptic vesicles. Nerve terminals without VIP reactivity had an EM appearance of cholinergic nerve terminals or were chrome positive (noradrenaline-containing) at X-ray micro-analysis, thus being adrenergic terminals. It is concluded that the porcine female genital tract is well innervated, along with adrenergic and cholinergic components, by VIP-containing nerves.