Human myometrial chorionic gonadotropin/luteinizing hormone receptors in preterm and term deliveries.

Nonpregnant human myometrium contains functional hCG/LH receptors. The present study investigated whether pregnant human myometrium also contains these receptors and whether they vary as a function of delivery in preterm or term pregnancies. Northern blotting revealed that pregnant human myometrium contains 4.3- and 2.2-kilobase receptor messenger ribonucleic acid transcripts. Immunoblotting with a specific hCG/LH receptor antibody showed that myometrium contains 70- and 50-kilodalton immunoreactive proteins. Ligand blotting demonstrated that only the 50-kilodalton protein could bind [125I]hCG, and this binding was inhibited by excess unlabeled hCG. In situ hybridization and immunocytochemistry revealed that the receptor messenger ribonucleic acid and receptor protein are present in myometrial and vascular smooth muscle. The myometrial smooth muscle receptor levels were lower during labor compared to those before labor at preterm and term pregnancy. In summary, our study demonstrates that pregnant human myometrium express hCG/LH receptor gene. The receptor levels were lower during labor compared to those before labor in preterm or term pregnancy. These data suggest that hCG, via its receptors, may contribute to myometrial quiescence until labor begins at the end of pregnancy.