Changes in uterine receptor mRNAs for oxytocin and estrogen in the pseudopregnant rat.

This study examined the uterine oxytocin- (OTR) and estrogen- (ER) receptor mRNA levels during and after pseudopregnancy (PSP) in rats. An increased OTR mRNA level was observed from day 14 of PSP, and the maximal level was attained during the following proestrus. The levels of ERalpha mRNA were low during PSP and significantly increased during the following estrus. The level of ERbeta mRNA was significantly decreased during proestrus and then returned to the values observed during days 7-14 of PSP by estrus. These results suggest i) suppression of ERalpha mRNA during the luteal phase and that ii) the changes in OTR, ERalpha and ERbeta mRNA levels during proestrus and estrus following PSP are similar to those during the normal estrous cycle.