Study of the effects of progesterone therapy on the stilboestrol-induced sensitivity of isolated uteri of hypophysectomized rats.

1. In intact rats progesterone (50 mg/kg) antagonized the effect of stilboestrol (100 mug/kg) on the vaginal smears and the uterine sensitivity. The uterine sensitivity to acetylcholine, oxytocin and 5-hydroxytryptamine was decreased by 6.8, 64 and 14.8 times, respectively, as compared with uteri removed after stilboestrol injections.2. Progesterone therapy in hypophysectomized rats also antagonized the effect of stilboestrol on the vaginal mucosa and on the uterine sensitivity to drugs. The sensitivity to acetylcholine, oxytocin and 5-hydroxytryptamine was decreased by 6.2, 50 and 14.5 times, respectively. Similar results were obtained on uteri removed from sham-hypophysectomized rats.3. On the basis of these results it is suggested that the hypophysis does not play any part in the desensitization of the myometrium to the oxytocic drugs and in the changes found in the vaginal mucosa after progesterone therapy.