Expression and localization of the contractile prostaglandin F receptor inpregnant rat myometrium in late gestation, labor, and postpartum

A polyclonal antibody was raised against amino acids 7-18 in the first extr acellular loop of rat prostaglandin F (FP) receptor to monitor expression a nd localization in pregnant rat myometrium at Gestational Days 16, 18, 20, 21, 21.5, 22 (delivery), and 23 (1-day postpartum; n = 5 per group). The an tibody recognized a protein of approximately 43 kDa on Western blot analysi s in both membrane (soluble and nonsoluble) and cytosolic fractions of myom etrium on each day of gestation. Expression of Fl? protein increased signif icantly (P < 0.05) during late gestation in both soluble membrane and cytos olic fractions, being significantly greater at Day 21.5 than at Day 20 of g estation in the soluble membrane fraction and in the cytosolic fraction of tissues collected during labor compared with those obtained before labor. T he total concentration of FP receptor in the membrane (soluble plus nonsolu ble) remained high throughout late gestation and fell significantly (P < 0. 05) in the postpartum period. The FP receptor in the soluble membrane fract ion (compared to the total membrane FP receptor) was significantly (P < 0.0 5) higher in late gestation than earlier, whereas the ratio of FP protein i n cytosolic to that in the total membrane was significantly (P < 0.05) high er on Day 23 than earlier in gestation, suggesting a dynamic movement of FP with advancing gestational age. Immunoreactive Fl? receptor localized to c ircular and longitudinal smooth muscle at all gestational ages, but changes in intracellular localization were observed in late gestation with a stain ing pattern similar to alpha -actin, suggesting an association with myofibr ils. Our study suggests an increase in FP-receptor protein in myometrium wi th advancing gestation and a marked elevation at term. This supports a role for uterine Fl? receptors in mediation of uterine contractility at term.