The morphofunctional pattern of neuronal biogenic amines in postpartum involution period-an in vivo study

Postpartum uterine diseases are associated with significant imbalance in the levels of biogenic amines (BAs) in rat uterus. Mast cells (MCs) are the main suppliers of BAs such as serotonin, catecholamines, and histamine in uterus. There is limited evidence of the BA-positive elements involved in the physiological regulation of uterus during postpartum involution. The aim of present study is to determine the concentration and distribution of biogenic amines (BAs) such as histamine, serotonin, and catecholamines in the uterine endometrium, myometrium, and peritoneal fluid (PF) during the postpartum uterine involution. A total of 110 nulliparous outbred female nonpregnant Wistar rats of mature age were divided into eleven groups (n=10 per group) according to days of postpartum involution. Tissue specimens of uterine segments, PF were prepared. Serotonin, catecholamines, and histamine concentrations were examined by fluorescence-histochemical techniques. The fluorescence of the BA-positive elements was detected and analyzed by microspectrofluorimetry. Results were analyzed using the Kruskal-Wallis chi-squared test and pairwise Mann-Whitney-Wilcoxon tests with "Benjamini-Hochberg correction" in R 3.6.3. Mast cells in uterine segments, PF exhibited characteristic yellowish-green fluorescence. The highest MCs number was reported in corpus uteri on the 15th day of postpartum involution. Serotonin, catecholamines, and histamine levels were significantly higher in BA-positive elements in the initial days. BA content was dynamic and relies on the time elapsed after parturition. There was statistically significant difference in the levels of BAs in the cornu and cervix uteri. A single morphofunctional complex of BA supply was noticed in the reproductive system of the rats. The coupled interactions of intra- and extra-organic BA-positive elements was associated with anabolic/catabolic equilibrium in uterus through the metabolism of serotonin, catecholamines, and histamine during postpartum involution.