Myometrial inhibiting activity of relaxin-containing extracts of human corpora lutea of pregnancy.

Relaxin is a peptide hormone secreted by the human corpus luteum of pregnancy . Aqueous extracts of relaxin-rich pregnancy corpora lutea decreased the amplitude of spontaneous human myometrial strip contractions in vitro. Relaxin-poor extracts of menstrual cycle corpora lutea did not affect contractions. Antibody precipitation of relaxin from pregnancy luteal extracts eliminated the effect on myometrial strips. Relaxin removal was confirmed by bioassay. This demonstrates an inhibiting action of human relaxin on human myometrial tissue in vitro. This action suggests a mechanism for maintaining uterine quiesence in early pregnancy.