Rats given progesterone subcutaneously on the 3rd day of life were studied to compare their reproductive capacity with that of oil-injected control females.
Females treated with 5 mg of progesterone showed an extremely high mortality rate. Of those surviving, the typical progesterone-treated female, when adult, showed: persistent vaginal cornification and infertility, ovaries weighing less than normal, absence of corpora lutea yet many large follicles with degenerate ova. After castration and treatment with ovarian hormones they show few or no lordoses in response to male mounts.
Similar results have been reported before as due to neonatal testosterone or estrogen treatment. In contrast to the almost invariable results seen with high doses of testosterone or estrogen, however, as many as 50% of the females treated with 5 mg of progesterone may not show one or more of the above reproductive features. Females treated with 1.25 or 2.50 mg of progesterone showed greater survival and fewer reproductive effects.