Effects of ovarian steroids on plasma LH in normal and persistent estrous adult female rats.

The ability of ovarian steroids to influence the release of LH was examined after ovariectomy in regularly cycling adult female rats and two types of anovulatory persistent estrous rats: rats treated with 10 mug of testosterone propionate (TP) shortly after birth, and normal rats housed under constant illumination. Two months after ovariectomy the negative feedback effects of a single injection of 20 mug estradiol benzoate (EB) on plasma LH were measured in these three preparations. Ovariectomized (ovex) normal and TP-treated but not ovex constant light-exposed rats had reduced LH values 6 hr after EB treatment. However, LH levels were reduced by the next day in rats in constant light. Positive feedback was measured in similar EB-primed rats following a second injection of EB or progesterone (P). In ovex normal rats LH values remained low in the morning but increased in the afternoon following the second steroid injection. Ovex EB-primed androgenized rats failed to demonstrate this positive feedback. Similarly, in ovex EB-primed constant light-exposed rats, LH values did not increase after a second EB injection. However, high LH values were observed in the afternoon 6 hr after P administration and again 40 and 50 hr later. These results indicate that the lack of spontaneous ovulation in androgenized rats may be due to the absence of positive feedback to ovarian steroids. Constant light-exposed ovex rats do not respond to the positive feedback action of estrogen and show a different response to P than ovex normal rats, in that a regular diurnal peak in plasma LH is not observed.