Prostaglandin receptors in lower segment myometrium during gestation and labor.

OBJECTIVE

To determine if expression of relaxatory prostaglandin (PG) E2 receptors (EP2 isoform) and contractile PG F receptors (FP isoform) changes during gestation and with labor in pregnant human myometrium.

METHODS

Lower segment myometrium was removed at cesarean from four groups of parturients (preterm [28-36 weeks] or term [37-41 weeks], either in or not in labor, ten per group). Myometrial RNA was isolated and used for reverse transcription-polymerase chain reaction (PCR) analysis with specific primer sets for human smooth muscle protein calponin and PGEP2 or FP receptor isoform mRNA. Polymerase chain reaction products were electrophoresed on gels and visualized, band intensity was measured, and EP2 and FP receptor expression was normalized to calponin.

RESULTS

Reverse transcription-PCR yielded products of expected sizes, and restriction enzyme cleavage confirmed identities. Prostaglandin EP2 receptor isoform mRNA expression (relative to calponin mRNA) was significantly greater in the preterm, no labor group (1.28+/-0.22, mean +/-standard error of the mean [SE]) compared with the term, no labor group (0.71+/-0.09) (P < .05 Student-Neuman-Kuels) and declined significantly with gestational age in patients not in labor (R = -.446, P = .001). Prostaglandin FP receptor isoform mRNA expression was significantly less in the term, no labor group (0.61+/-0.06) compared with all others (P < .02 Student-Neuman-Kuels). Prostaglandin FP receptor expression declined significantly with gestational age in patients not in labor (R = -.646, P = .012) and increased significantly with labor at term.

CONCLUSION

Changes in prostaglandin EP2 receptor isoform expression are consistent with influence on maintenance of quiescence. Labor at term is associated with a significant increase in FP receptor expression, consistent with influence on contraction. The balance between the two receptor isoforms might mediate myometrial contractility.