Expression and Localization of the Contractile Prostaglandin F Receptor in Pregnant Rat Myometrium in Late Gestation, Labor, and Postpartum1

Abstract

A polyclonal antibody was raised against amino acids 7-18 in the first extracellular loop of rat prostaglandin F (FP) receptor to monitor expression and 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 antibody recognized a protein of approximately 43 kDa on Western blot analysis in both membrane (soluble and nonsoluble) and cytosolic fractions of myometrium on each day of gestation. Expression of FP protein increased significantly (P < 0.05) during late gestation in both soluble membrane and cytosolic fractions, being significantly greater at Day 21.5 than at Day 20 of gestation in the soluble membrane fraction and in the cytosolic fraction of tissues collected during labor compared with those obtained before labor. The total concentration of FP receptor in the membrane (soluble plus nonsoluble) remained high throughout late gestation and fell significantly (P < 0.05) in the postpartum period. The FP receptor in the soluble membrane fraction (compared to the total membrane FP receptor) was significantly (P < 0.05) higher in late gestation than earlier, whereas the ratio of FP protein in cytosolic to that in the total membrane was significantly (P < 0.05) higher on Day 23 than earlier in gestation, suggesting a dynamic movement of FP with advancing gestational age. Immunoreactive FP receptor localized to circular and longitudinal smooth muscle at all gestational ages, but changes in intracellular localization were observed in late gestation with a staining pattern similar to alpha-actin, suggesting an association with myofibrils. Our study suggests an increase in FP-receptor protein in myometrium with advancing gestation and a marked elevation at term. This supports a role for uterine FP receptors in mediation of uterine contractility at term.

Intraperitoneal infusion of proinflammatory cytokines does not cause activation of the rat uterus during late gestation

“…Our findings of increased expression of mRNA for FP receptor and Cx-43 levels during uterine activation are consistent with the data from others in mouse (11), rat (1,35), and human myometrium (7,18,50). However, there is no direct evidence linking regulation of these genes with cytokine stimulation.…”

Ablation of connexin43 in uterine smooth muscle cells of the mouse causes delayed parturition

“…During late gestation, OT receptors (OTR) and prostaglandin F receptors (FP) are significantly induced in the myometrium in many mammalian species (Challis and Lye, 1994;Zingg et al, 1995;Imamura et al, 2000;Al-Matubsi et al, 2001; Arosh , 2004). In rats, the gestational profiles of the expressed Fos gene showed significantly higher transcript levels only during labour (Piersanti and Lye, 1995;Mitchell and Lye, 2002).…”

A decline in the levels of progesterone receptor coactivators in the pregnant uterus at term may antagonize progesterone receptor function and contribute to the initiation of parturition

“…mRNA levels for other coregulators (steroid receptor RNA activator, nuclear receptor corepressor, silencing mediator for retinoid and thyroid hormone receptor, Alien, and RIP-140) (10)(11)(12) and proteins that facilitate PR DNA binding (highmobility group proteins 1 and 2) (13) were variable, with no obvious trend between the in-labor and not-in-labor samples (data not shown). It has previously been reported that CnX43, OTR, and PGF 2␣ R are expressed in pregnant myometrium and increase with the onset of labor (14)(15)(16). To confirm at the molecular level that the myometrial tissues were classified correctly with regard to ''labor'' status, mRNA levels for the gap junction protein, CnX43, the OTR, and PGF 2␣ R were analyzed by using semiquantitative RT-PCR.…”