Changes in Uterine Receptor mRNAs for Oxytocin and Estrogen in the Pseudopregnant Rat

Abstract

ABSTRACT. 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 ERα mRNA were low during PSP and significantly increased during the following estrus. The level of ERβ 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 ERα mRNA during the luteal phase and that ii) the changes in OTR, ERα and ERβ mRNA levels during proestrus and estrus following PSP are similar to those during the normal estrous cycle. KEY WORDS: estrogen receptor, oxytocin receptor, pseudopregnancy.J. Vet. Med. Sci. 70(11): 1253-1256, 2008 Oxytocin (OT) was initially isolated as a neurohypophysial hormone that stimulates contraction of the myometrium and myoepithelium to facilitate parturition and milk ejection, respectively, and is considered to mediate various reproductive functions in the ovary, uterus and brain. In the uterus, the near-term myometrium is extremely sensitive to oxytocin. This increased uterine responsiveness to oxytocin occurs in parallel with an increase in the number of uterine oxytocin binding sites in rats [3,21], humans [4], rabbits [13,14] and cows [5]. Corresponding increases in uterine oxytocin receptor (OTR) mRNA expression in late pregnancy and parturition have been reported in rats [11,12,19], humans [9], cows [8] and sheep [24,25].Estrogen stimulates the number of uterine oxytocin binding sites [3,20,22] and OTR mRNA expression in ovariectomized (OVX) virgin rats [11,12]. However, injection of estrogen does not stimulate oxytocin receptor mRNA expression in late pregnant rats or progesterone-primed OVX virgin rats, but is effective only after ovariectomy and removal of progesterone, respectively [17]. These results suggest that in addition to the increase in serum estrogen level near term in rats, regulation of the uterine responsiveness to estrogen is important for understanding the role of estrogen in the uterus. The actions of estrogen are mediated through estrogen receptors [1], and two types of estrogen receptor (ER), ERα and ERβ, have been cloned from the human uterus [6] and rat prostate [10], respectively.In the rat uterus at the end of pregnancy and during labor, the ERα mRNA level gradually increases simultaneously with the OTR mRNA level, while the ERβ mRNA level does not show any significant changes; during this period, there is a positive correlation between the ERα and OTR mRNA levels [16]. However, while the OTR mRNA level is increased during proestrus and then decreased during estrus in the estrous cycle, the ERα and ERβ mRNA levels decrease during proestrus and return to the levels observed during diestrus at estrus [15,16]. This indicates apparent reciprocal changes between OTR and ER (ERα and ERβ) mRNA levels during proestrus and estrus. Furthermore, injection of 17...

Temporal and Spatial Regulation of Let-7a in the Uterus During Embryo Implantation in the Rat

“…Pseudopregnancy was induced in Sprague Dawley female rats by mating with male rats two weeks after vasectomy, and mating was confirmed by checking for a vaginal plug (day 1 of pseudopregnancy) [23,24]. These were no fertilized eggs in the vaginas of the pseudopregnant rats.…”

“…This suggested that only the state of endometrial receptivity or dormant blastocysts did not increase the expression of let-7a. Let-7a expression was significantly induced by the process of embryo invasion, implying that let-7a may participate in endometrial decidualization.To further explore whether let-7a expression is associated with the induction of implantation, we tested the effects of pseudopregnancy, experimentally induced decidualization and delayed implantation.Pseudopregnancy was induced in Sprague Dawley female rats by mating with male rats two weeks after vasectomy, and mating was confirmed by checking for a vaginal plug (day 1 of pseudopregnancy) [23,24]. These were no fertilized eggs in the vaginas of the pseudopregnant rats.…”