Morphological and functional characterization of a rat vaginal smooth muscle sphincter

Abstract

The aim of the present study was to gain information about adrenergic-, cholinergic- and non-adrenergic, non-cholinergic (NANC)- transmitter systems/mediators in the rat vagina, and to characterize its smooth muscles functionally. Tissue sections from vagina of Sprague Dawley rats were immunolabelled with antibodies against protein gene product 9.5 (PGP), synaptophysin (Syn), tyrosine hydroxylase (TH), vesicular acetylcholine transporter (VAChT), neuropeptide Y (NPY), nitric oxide synthase (NOS), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP). Circularly cut vaginal smooth muscle preparations from the distal vagina were studied in organ baths. In the paravaginal tissue, a large number of PGP-, NOS-, TH-, VIP-immunoreactive (IR) and few CGRP-IR nerve trunks were observed, giving off branches to the smooth muscle wall. The smooth muscle wall was supplied by a large number of PGP-, Syn-, VAChT-, NPY-, NOS- and TH- IR nerve terminals, whilst only a moderate to few numbers of CGRP-, VIP- and PACAP-IR terminals were identified. Especially the distal part of the vaginal wall, where the circularly running smooth muscle was thickened into a distinct sphincter structure, was very richly innervated, predominantly by PGP- and NOS-IR terminals. Below and within the basal parts of the epithelium in the distal half of the vagina, a large number of PGP- and few NOS- and PACAP-IR varicose terminals were observed. The vaginal arteries were encircled by plexuses of nerve terminals. A large number of these were PGP-, Syn-, VAChT-, NOS-, TH-, NPY- and VIP-IR, and few were CGRP- and PACAP-IR. In isolated preparations of the distal vagina, electrical field stimulation (EFS) caused frequency-dependent contractions, which were reduced by sildenafil, tetrodotoxin (TTX) and phentolamine. In preparations contracted by norepinephrine (NA), EFS produced frequency-dependent relaxations. Pretreatment with the NOS-inhibitor N(G)-nitro-L-arginine, TTX, or the inhibitor of soluble guanylate cyclase, ODQ, abolished the EFS relaxations. In NE precontracted preparations, cumulative addition of sildenafil caused concentration-dependent relaxation. Carbachol contracted the strips concentration-dependently from baseline. It can be concluded that the distal part of the rat vagina forms a distinct smooth muscle sphincter, which is richly innervated by adrenergic, cholinergic and NANC nerves. The present studies suggest that in the rat the L-arginine/NO-system not only plays an important role in the regulation of vaginal smooth muscle tone, but also affects blood flow, and may have sensory functions.

Regional Differences in Rat Vaginal Smooth Muscle Contractility and Morphology

“…In prior EFS studies, Giraldi et al 12 were able to induce frequency-dependent contractions in the distal vagina at 1 to 50 Hz, but reported no or weak responses using circular proximal strips. We were able to demonstrate a contractile response to 1 to 64 Hz in all vaginal regions (proximal, middle, and distal).…”

“…Smooth muscle bundles in the vaginal wall are supplied by nerve fibers expressing protein gene product (PGP 9.5), vesicular acetylcholine transporter (VAChT), tyrosine hydroxylase (TH), as well as various other nerve fibers, and the distal vagina is particularly well-innervated. 12 The PGP 9.5 is a cytoplasmic protein expressed in all peripheral nerves, VAChT mediates acetylcholine storage by synaptic nerves, and TH catalyzes the conversion of the amino acid L-tyrosine to dihydroxyphenylalanine. The PGP 9.5 is therefore used as a specific marker for total peripheral innervation, while VAChT and TH are used as specific markers of cholinergic and adrenergic nerve fibers, respectively.…”

Effects of diabetes on neurotransmission in rat vaginal smooth muscle

“…The mean weight of the diabetic animals was 200 AE 4 g, and that of the control group 257 AE 3 g. After killing the animals a vaginal smear was done in order to determine the oestrous cycles of the animals, as described by Giraldi et al 3 Blood glucose was measured in blood from the carotid artery. Thereafter the abdomen was opened and the uterus, bladder and vagina were removed and placed in chilled Krebs Ringer (for composition see below).…”

“…The Krebs solution had the following composition (mM): NaCl 119, KCl 4.6, CaCl 2 1.5, MgCl 2 1.2, NaHCO 3 …”

“…In the human and animal vagina, adrenergic-, cholinergic-as well as non-adrenergic, non-cholinergic (NANC)-neurotransmittersatransmitter generating enzymes have been identi®ed as described previously. 3 However the exact role of these neurotransmitter systems in the regulation of vascular and vaginal smooth muscle during the sexual response still remains to be established.…”