Inhibition of oxytocin receptor function by direct binding of progesterone

Pregnancy maintenance in animals relies on the steroid hormone progesterone (P4), which maintains uterine inactivity by reducing uterine sensitivity to the uterotonic peptide hormone oxytocin. A new study reveals that P4's effect on uterine sensitivity to oxytocin involves a non-genomic action on the uterine oxytocin receptor, which belongs to the G-protein-coupled receptor family. This is the first evidence of a functional interaction between a G-protein linked member and a steroid.