Gestrinone

Gestrinone has weak agonist activity on progesterone receptors in the rabbit endometrium and progesterone antagonist activity in various other pharmacological test systems. In addition, it has moderate agonist activity on prostatic androgen receptors in vitro. In several in vivo experiments, this activity was found to be low.

The primary action of gestrinone is on the hypothalamic-pituitary axis where it inhibits gonadotrophin release with a weak inhibitory effect on its synthesis. It also possesses anti-estrogen activity. The suppression of the ovular gonadotrophin peak is observed after the first month of treatment; the resulting decline in ovarian hormone secretion rapidly leads to endometrial atrophy. Aside from its central action, gestrinone also has anti-progesterone activity on cell receptors in both endometrium and extra-uterine ectopic implants. Gestrinone has no direct estrogen and/or uterotrophic effects.

A study was done to examine the efficacy of gestrinone in emergency contraception. The data from the study suggest that the mechanism of action of gestrinone used for the purposes of emergency contraception is likely the inhibition of implantation by acting on the endometrium as opposed to the inhibition of ovulation.