Regulation of Myometrial Gi2, Gi3, and Gq Expression during Pregnancy. Effects of Progesterone and Estradiol1

Abstract

The possibility that progesterone or estradiol may regulate expression of G protein in the rat myometrium during the course of pregnancy has been investigated using 1) immunoblot analysis of Gi2 alpha, Gi3 alpha, and Gq alpha subunits and 2) hybridization blot analysis of subunit mRNA. Eighteen hours after administration, estradiol had significantly increased the levels of both Gi2 alpha subunit and Gi2 alpha mRNA (by 40% and 32%, respectively). In control pregnant rats, we observed similar changes at the end of pregnancy, when myometrial concentrations of estradiol had increased, i.e., a 41% increase in immunoreactive Gi2 alpha subunit that correlated with a parallel 45% increase in mRNA levels. In contrast, levels of immunoreactive Gi3 alpha subunit and mRNA, which decreased with advancing gestation, were not influenced by estradiol or progesterone administration. Progesterone administration resulted 30 h later in a significantly decreased level of Gq alpha immunoreactivity (32%) and Gq alpha mRNA (30%). In control rats, Gq alpha protein and mRNA were also significantly lower at midpregnancy under progesterone dominance vs. term. At this stage, a twofold increase in Gq alpha subunit correlated with a 40% increase in mRNA levels. These results demonstrate that myometrial Gi2 alpha and Gq alpha subunits are physiological targets for estradiol and progesterone, respectively, in vivo. Alterations of these G protein levels are discussed in relation to their mediating effects on adenylyl cyclase activity or the phospholipase C pathway during the course of pregnancy.

Up-regulation of rat myometrial phospholipases Cβ1 and Cβ3 correlates with increased term sensitivity to carbachol and oxytocin

“…Control rats received the same volume of oil subcutaneously on the same schedule. The doses of progesterone and oestradiol administered significantly increased the myometrial levels of both steroids as we have determined in previous works (ElwardyMérézak et al 1994, Cohen-Tannoudji et al 1995.…”

“…Furthermore, the pattern of PLC 1 and PLC 3 expression correlates well with that of their cognate Gq protein. Indeed, we have previously reported a 120% increase in the amount of rat myometrial Gq protein between day 12 of pregnancy and term (Cohen-Tannoudji et al 1995). In addition, as for PLC 1 and PLC 3, the amount of Gq protein is maximal from day 21 of pregnancy (CohenTannoudji et al 1995).…”

“…Our results also indicated that, under our treatment conditions, myometrial PLC 1 and PLC 3 are insensitive to progesterone. Using a similar protocol, we have previously reported that progesterone significantly reduces the expression of rat myometrial Gq (Cohen-Tannoudji et al 1995).…”

“…At term, the increased expression of Gq and PLC 1 and PLC 3 due to progesterone withdrawal and oestrogen increase respectively may underlie the enhancement of uterine responsiveness to uterotonic factors. In myometrium, the expression of many proteins including OTR, connexin-43, cyclo-oxygenase 2 and Gi2 protein was shown to be regulated at the transcriptional level by oestradiol (Larcher et al 1995, Lefebvre et al 1995, Cohen-Tannoudji et al 1995, Wu et al 1997). Whether or not oestradiol controls the expression of PLC 1 and PLC 3 at the transcriptional or post-transcriptional level remains to be determined.…”

“…The days of steroid administration were chosen on the basis of our previous studies where myometrial concentrations of progesterone and oestradiol were determined during the course of pregnancy (Elwardy-Mérézak et al 1994, Cohen-Tannoudji et al 1995. Progesterone and oestradiol were thus delivered to rats when their myometrial endogenous levels are low, i.e.…”