Expression of regulator of G protein signaling-2 in rat myometrium during pregnancy and parturition

The purpose of this study was to determine the potential physiologic roles of myometrial regulator of G protein signaling-2 (RGS2), a G protein-associated GTPase, by the analysis of the changes in RGS2 messenger RNA expression during pregnancy and parturition and to examine factors that regulate these changes.

Myometrial RGS2 messenger RNA levels were analyzed by Northern blotting in rats (1). during pregnancy, parturition, and in the postpartum period; (2). with preterm-induced and delayed, postterm delivery; (3). that were ovariectomized and treated with either estradiol, progesterone, or both; and (4). with unilateral uterine pregnancies.

RGS2 messenger RNA was almost undetectable until day 5 of pregnancy, when it rose sharply and remained elevated up to and including day 19, at the time that progesterone withdrawal occurs. The expression of myometrial RGS2 messenger RNA on day 22 did not differ between rats either before or during delivery. Onapristone caused preterm delivery and a premature fall in RGS2 messenger RNA levels. In contrast, progesterone treatment prolonged pregnancy beyond day 25 and attenuated the decline in RGS2 messenger RNA levels. Simulation of the first 5 days of pregnancy resulted in a 3-fold rise in RGS2 messenger RNA expression. The levels of RGS2 in nonimplanted horns were approximately one half that of pregnant horns.

Sex steroids, in particular progesterone, and the presence of the conceptus play a role in the regulation of myometrial RGS2 messenger RNA expression. Although the elevated myometrial RGS2 messenger RNA expression corresponds to the period during pregnancy when the uterus is relatively quiescent and the down-regulation of RGS2 messenger RNA at the end of pregnancy may be related to the timing of parturition, the specific role of myometrial RGS2 remains unknown.