The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on weight gain and hepatic ethoxyresorufin-o-deethylase (EROD) induction vary with ovarian hormonal status in the immature gonadotropin-primed rat model

Immature female rats received 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) du ring an induced proestrus or diestrus. The inhibitory effect of TCDD on acu te weight gain and the induction of hepatic ethoxyresorufin-o-deethylase (E ROD) activity by TCDD were greatest during proestrus. In a second experimen t, ovariectomized rats received estradiol cypionate (ECP) or progesterone f ollowed by TCDD. TCDD and estradiol each alone significantly inhibited weig ht gain. Progesterone potentiated the effects of TCDD on weight gain. The h ighest dose of ECP was associated with greater induction of hepatic EROD ac tivity by TCDD than seen with TCDD alone. Estradiol modulates the induction of hepatic EROD activity by TCDD. Differential effects: of TCDD on acute w eight gain during proestrus vs, diestrus in this model do not mimic changes induced by estrogen alone. Hepatic responses to TCDD may vary according to phase of the female reproductive cycle. (C) 2001 Elsevier Science Inc. All rights reserved.