The Role of Neurogenic Bioamines in Nerve Fibers of Uterus during the Postpartum Involution in Experimental Animal Models

BACKGROUND: Biogenic amines (BAs) secreted by the sympathetic neural apparatus of rat uterus are reported to be conducive to the uterine functional activity during postpartum involution; the imbalance in BAs ratio could confer postpartum reproductive disorders including improper postpartum involution. OBJECTIVE: The objective of this study is to identify the changes in the density of uterine sympathetic nerves implicated in the pathology of endometriosis, adenomyosis, and delayed uterine involution. The present study aims to ascertain 'serotonin' and 'catecholamine' concentrations in mesenteric mast cells (MCs), and structural elements of nerve fibers across the perivascular plexuses (PPs) and single sympathetic nerve terminals (SST). METHODS: Furthermore, the density of their spatial distribution (SDP and SDT) in the uterine body, cervix, and mesometrium was determined during postpartum involution. Tissue specimens of postpartum uterus were obtained from 55 nulliparous female Wistar outbred strain rats, which were grouped according to the days after parturition at the time of sacrifice. The nerve fibers of PP and SST exhibited emerald green fluorescence, which was detected by glyoxylic acid fluorescence technique; the fluorescence invoked by BAs was identified by microspectrofluorimetry. RESULTS: Concentrations of BAs were extensive in the varicosities of PP and SST on the 10th day. However, the highest BA concentrations were found in structural elements of PP in the uterine mesometrium in the initial days of postpartum. In mesenteric MC, serotonin and catecholamines were at the highest concentration on the 10th day of postpartum. Histamines peaked on the 6th day. CONCLUSION: SDP and SDT were increased significantly in all structural elements of uterine nerve fibers in the uterine body and cervix compared to SDP in mesentery. Considering that catecholamines and serotonin are antagonists in many aspects of their biological action, the ratio of BAs should be well-balanced to maintain anabolic- catabolic equilibrium in the rat uterus.