Innervation of vasculature and microvasculature of the human vagina by NOS and neuropeptide-containing nerves

Abstract

The aims of the present study were to determine whether nerves that contain nitric oxide synthase (NOS), calcitonin gene-related peptide (CGRP) or substance P (SP) are present in the human vagina and, if so, to determine the pattern of innervation relative to that of other neurotransmitters, particularly vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY). Surgical specimens of vaginal tissue (n = 10) from pre- and postmenopausal women were fixed and processed for immunohistochemistry of peptides and NOS and for histochemistry of NADPH-diaphorase. SP-immunoreactive nerves were very sparse, being absent from 9 of the 10 tissue samples. For other peptides and NOS, the innervation of the deep arteries and veins was greater than that of blood vessels in the propria. Capillaries in the epithelial papillae also appeared to be innervated by nerves containing NOS, CGRP, NPY and VIP. Beneath the epithelium nerve fibres formed a subepithelial plexus; no nerve cell bodies were seen. The relative density of innervation by immunoreactive fibres was PGP-9.5 > NPY > VIP >> NOS > CGRP > SP. These results imply that nerves that utilise nitric oxide or NPY, VIP or CGRP as a neurotransmitter may play a role in controlling blood flow and capillary permeability in the human vagina. The origin and function of all these nerves is discussed.