Effects of dexamethasone on ovarian activity in rats

Rats with 5-day ovarian cycles were treated with dexamethasone (0.025 to 0.4 mg per rat per day) to examine its effects on ovarian activity. All doses of dexamethasone markedly suppressed endogenous secretion of ACTH as evidenced by decrease in weight of the adrenal glands after 7-23 days of treatment. Treatment with 0.4 mg of dexamethasone from the day of ovulation appeared to induce pseudopregnancy in more than 90% of the rats studied: pseudopregnancies lasted for 14-22 days. Induction of pseudopregnancy occurred less, in a dose-dependent fashion, when the lower doses of dexamethasone were administered. However, prolonged treatment with these lower doses resulted also in pseudopregnancy albeit after 1 or more cycles of 5 to 7 days. The effects of large doses of glucocorticoids on ovarian activity in rats, and possibly in humans as well, may be mediated predominantly through a stimulatory action of such drugs on prolactin secretion. Treatment with 0.4 mg per day of dexamethasone from the day before pro-oestrus did not interfere with ovulation and pseudopregnancy ensued this ovulation in all rats studied. Occasionally, unexpectedly large numbers of eggs per ovulating animal were found during treatment with dexamethasone. The data indicate failure of large doses of dexamethasone to interfere with ovulation and, possibly, induction of an increase in numbers of maturing follicles: this latter action deserves further analysis.