Interaction of estradiol and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inan ovulation model: evidence for systemic potentiation and local ovarian effects

Immature rats were treated with estradiol cypionate, (ECP, 0, 0.1, 1, or 2 mg/kg s.c.) followed 24 h later by TCDD (0 or 10 mu g/kg orally). Follicula r development was induced with eCG [5 or 10 IU subcutaneously (s.c.)] follo wed by an ovulatory dose of hCG (10 IU s.c.). Inhibition of ovulation by TC DD was potentiated by ECP in hypophysectomized but not intact rats. Only hy pophysectomized rats exposed systemically to TCDD and ECP exhibited weight loss. Pair feeding mimicked the combined effects of TCDD and ECP in hypophy sectomized rats. In another experiment, intact rats received ECP s.c. (0 or 2 mg/kg) and TCDD into the ovarian bursa (0 or 250 ng). Another group of i ntact rats received TCDD orally (10 mu g/kg) and ECP into the ovarian bursa (0 or 1.5 mu g). Blockade of ovulation by systemic or local TCDD was allev iated by ECP pretreatment. Estrogen increased the systemic toxicity of TCDD in rats whereas antagonizing its direct ovarian effects. (C) 2000 Elsevier Science Inc. All rights reserved.