Changes in oxytocin receptor mRNA in the rat uterus measured by competitive reverse transcription-polymerase chain reaction

Abstract

Large changes in the responsiveness of target organs to oxytocin are thought to originate from alteration of the number of oxytocin receptors (OTR). To elucidate the molecular mechanisms regulating the synthesis of the OTR, we developed a competitive reverse transcription-PCR protocol to measure OTR mRNA. We synthesized cRNA comprising a small stuffer introduced into the target mRNA. Using this cRNA as an internal standard, we made a quantitative estimation of OTR mRNA. Application of this method to the rat uterus revealed that the mean levels of OTR mRNA remained unchanged until 1030-1100 h on day 21 of pregnancy, increased significantly after 2200-2230 h on the same day and declined rapidly after parturition. A similar rapid increase in uterine OTR mRNA content was observed in rats given prostaglandin on day 18, inducing premature delivery on day 19 of pregnancy. All parturient rats had higher OTR mRNA levels regardless of whether parturition was spontaneous or prostaglandin induced. However, in a few rats, OTR mRNA remained as low as that observed during mid pregnancy even on day 22 of gestation, the expected day of parturition in about 70% of the rats in our colony. A similar increase in uterine OTR mRNA content to that observed at parturition was induced by oestrogen treatment for 3 days in ovariectomized virgin rats, but concomitant injection of progesterone did not influence the effect of oestrogen. The present results revealed that the large increase of uterine OTR at the peripartum period is accompanied by an increase in OTR mRNA content that may be brought about, at least in part, by increased oestrogen secretion following luteolysis.

Sex, parturition and motherhood without oxytocin?

“…Thus there is a large increase in uterine oxytocin receptor mRNA content at the end of pregnancy in the rat (Liu et al 1996), and in the sheep there is a clear correlation between myometrial and endometrial oxytocin receptor mRNA and protein expression, and with myometrial contractile activity (Wu et al 1996). Similarly, oxytocin receptor mRNA and protein content in the human myometrium are greatly increased at the end of pregnancy (Kimura et al 1996).…”

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

“…1). These changes mimicked those during pregnancy, with increased expression at the end of pregnancy and during labor [12,17]. During estrus following PSP, the OTR mRNA level decreased significantly.…”

“…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].…”

“…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].…”

“…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].…”