Molecular endocrinology - Steroids tickle cells inside and out

Steroid hormones are classically thought to bind to receptors inside cells, acting through changes in gene expression. But a study of the hormone progesterone shows that it can also act on the outside of a cell. The authors have found that it can bind the oxytocin receptor, preventing the natural ligand — oxytocin — from binding. Because progesterone is involved in maintaining pregnancy whereas oxytocin has the opposite effect, inducing uterine contractions, these findings could be used in preventing pre-term labour.