Effects of progesterone therapy on the stilboestrol-induced sensitivity of isolated rat uterus preparations.

1. Progesterone treatment (50 mg/kg) in ovariectomized rats antagonizes the effects of stilboestrol 100 mug/kg on the vaginal mucosa and uterine weight; but the sensitivity to acetylcholine, oxytocin and 5-hydroxytryptamine is increased by factors 4, 11 and 3, respectively.2. In intact animals a similar progesterone treatment (50 mg/kg) antagonizes the effects of stilboestrol 100 mug/kg on vaginal smears, uterine weight and uterine sensitivity. The uterine sensitivity to acetylcholine, oxytocin and 5-hydroxytryptamine is, however, decreased by a factor of 2, 1.4 and 17.7, respectively.3. These experiments show that the ovary is essential for the desensitizing effects of progesterone. The suggestion is put forward that another substance is released from the ovary by progesterone.