Expression and regulation of the messenger ribonucleic acid encoding the prostaglandin F-2 alpha receptor in the rat myometrium during pregnancy and labor

OBJECTIVE: We examined expression of messenger ribonucleic acid encoding th e prostaglandin F-2 alpha receptor in the rat myometrium throughout late ge station and its regulation by progesterone and mechanical stretch. STUDY DESIGN: Normal pregnant rats were killed on gestational day 15, 22, o r 23 (during labor) or 1 day post partum. The effects of progesterone on pr ostaglandin F-2 alpha receptor messenger ribonucleic acid levels were inves tigated by daily injections of progesterone (4 mg) from day 20 of normal ge station or from day 17 in rats bilaterally ovariectomized on day 17. To inv estigate the effects of myometrial stretch, unilaterally pregnant rats unde rwent 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-2 alpha receptor messenger ribonucleic acid levels in the myometrium were determined by a semiquantitative reverse transcription-pol ymerase chain reaction method. RESULTS: Myometrial prostaglandin F-2 alpha receptor messenger ribonucleic acid levels significantly increased during both term and ovariectomy-induce d preterm labor. This increase was blocked by progesterone. In rats with un ilateral pregnancies prostagtandin F-2 alpha receptor messenger ribonucleic acid levels in the nongravid horns were similar to those in the contralate ral 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-2 alpha rece ptor messenger ribonucleic acid during term and preterm labor is temporally associated with progesterone withdrawal but is not dependent on mechanical stretch of the myometrium.