Objective: We examined expression of messenger ribonucleic acid encoding the prostaglandin F(2alpha) receptor in the rat myometrium throughout late gestation and its regulation by progesterone and mechanical stretch.
Study design: Normal pregnant rats were killed on gestational day 15, 22, or 23 (during labor) or 1 day post partum. The effects of progesterone on prostaglandin F(2alpha) receptor messenger ribonucleic acid levels were investigated by daily injections of progesterone (4 mg) from day 20 of normal gestation or from day 17 in rats bilaterally ovariectomized on day 17. To investigate the effects of myometrial stretch, unilaterally pregnant rats underwent either sham surgery or placement of a polyvinyl tube 3 mm in diameter in the nongravid uterine horn on day 15 or 18 and were killed 5 days later. Prostaglandin F(2alpha) receptor messenger ribonucleic acid levels in the myometrium were determined by a semiquantitative reverse transcription-polymerase chain reaction method.
Results: Myometrial prostaglandin F(2alpha) receptor messenger ribonucleic acid levels significantly increased during both term and ovariectomy-induced preterm labor. This increase was blocked by progesterone. In rats with unilateral pregnancies prostaglandin F(2alpha) receptor messenger ribonucleic acid levels in the nongravid horns were similar to those in the contralateral gravid horns on day 20 and during labor regardless of whether they were stretched by a 3-mm tube.
Conclusion: Increased myometrial expression of prostaglandin F(2alpha) receptor messenger ribonucleic acid during term and preterm labor is temporally associated with progesterone withdrawal but is not dependent on mechanical stretch of the myometrium.