Early Changes in Luteal Function Associated with the Luteotropic Effect of Testosterone in the Pregnant Rat1

The luteotropic effect of testosterone was investigated in pregnant rats by determining some of the early changes in luteal function associated with the action of this hormone after injection of LH antiserum. The injection of LH antiserum on Day 11 of pregnancy caused a decrease in serum progesterone and in luteal estradiol concentration within 6 h, and subsequently led to abortion. Treatment with a low dose of testosterone via Silastic capsule prevented abortion and the decrease in luteal estradiol and rapidly restored serum progesterone to values which were maintained at elevated, though distinctly lower, values than in control pregnant rats. The reduced serum progesterone in testosterone-treated rats was interpreted as the result of increased formation of 20α-dihydroprogesterone, which appeared in high concentrations within 24 h after injection of LH antiserum and remained elevated through Day 15 of pregnancy, the end of the experiment. In LH antiserum-treated rats without testosterone, the increment in 20α-dihydroprogesterone was also apparent within 24 h, but did not compensate for the sustained loss of progesterone secretion which preceded abortion. Corpora lutea retained aromatase activity in rats aborting after administration of LH antiserum, suggesting that this enzyme was not rate-limiting for estradiol formation in these regressing corpora lutea. These, together with other studies, provide further impetus to the idea that estrogens formed in luteal tissue mediate the sustained progesterone steroidogenic effect of LH. However, one important action of LH may be the suppression of 20α-dihydroprogesterone secretion, thus augmenting the secretion of progesterone.