Unilaterally ovariectomized pregnant mice: dieldrin induction of the hepatic monooxygenases and plasma progesterone levels.

Abstract

Plasma progesterone, pregnancy maintenance, gestation period, and litter size were measured in mice unilaterally ovariectomized on day 6 of pregnancy (plug day = day 0) and then treated daily with dieldrin (2 mg kg-1, p.o.). By days 15--16, dieldrin had reduced the pentobarbital sleep time by 54% (P < 0.05), increased the liver mass by 8% (P < 0.05), and increased hepatic microsomal cytochrome P-450 by 66% (P < 0.05). However, the levels of plasma progesterone in the hemiovariectomized, dieldrin-treated mice were not different from those in the hemiovariectomized controls. Other experiments showed that hemiovariectomy decreased plasma progesterone by about 25%. Moreover, hemiovariectomy increased the frequency of premature delivery but it did not affect litter size; dieldrin treatment did not alter these effects. The failure of the induction to reduce plasma progesterone could result from (1) increased progesterone synthesis compensating for its elevated metabolism or (2) no (net) increase in progesterone metabolism.