Expression of Oxytocin Receptor Protein in Gastrointestinal Tract of Lactating Rats.

The oxytocin receptor (OTR) is a typical class I G protein-coupled receptor that is mainly coupled via Gq proteins to phospholipase C-β. The function and physiological regulation of the OT system is strongly steroid-dependent. Recently, we found that OT treatment inhibited gastrointestinal motility in vivo and in vitro. Using a molecular cloning technique, OTR mRNA was observed in gastrointestinal tract of rats. The purpose of this study is to investigate the effects of lactation on OTR protein expression in gastrointestinal tract of female rats. OTR mRNA expression in gastrointestinal tract of either intact or ovariectomized (OVX) rats was detected by real time-polymerase chain reaction (RT-PCR). OTR protein was measured in gastrointestinal tract of rats on days 1-2, 7-8, 15 and 21 of lactation, on day 7 postweaning, and at the nonpregnant diestrus stage. All animals were fasted for 24 h. On the experimental day, rats were decapitated. Proteins from liver, stomach, small intestine, mammary gland and uterus were isolated. OTR protein was analyzed by the analysis of Western blot. All data were expressed as mean ± SEM, and analyzed by the analysis of variance (ANOVA) and Duncan's multiple range tests. OTR mRNA was demonstrated in the gastrointestinal tract of rats. Expression of OTR protein was decreased in stomach and duodenum of OVX rats. In the gastrointestinal tract, there was no significant difference in OTR protein expression on the uterus among lactating, post-weaning and diestrus rats. OTR protein expression was decreased in antral mucosa and smooth muscle in the early stage of lactation. There was no difference in OTR protein expression on the mucosa and smooth muscle of stomach body, duodenum, jejunum and ileum among lactating, post-weaning, and diestrus rats. These results suggested that OTR mRNA was detectable in the gastrointestinal tract of rats and the OTR protein expression in rat gastrointestinal tract was decreased during early lactation.