Estradiol-17β and o,p′-DDT stimulate gonadotropin release in Atlantic croaker

Xenobiotic estrogens have the potential to act at a variety of estrogen-responsive target tissues on the hypothalamic-pituitary-gonadal axis. However, to date most studies in fish have focused on stimulation of vitellogenin synthesis by the liver, In the present study the effects of the xenoestrogen o,p'-DDT and estradiol-17 beta on the neuroendocrine control of gonadotropin secretion were compared. Atlantic croaker (Micropogonias undulatus) were exposed to o,p'-DDT (0.02 and 0.1 mu g g(-1) body weight day(-1)) in the diet for 3 and 7 weeks during the gonadal recrudescence phase, The o,p'-DDT exposure elicited a significant increase in plasma gonadotropin levels after both 3 and 7 weeks of exposure. The stimulatory effect of o,p'-DDT on basal (spontaneous) gonadotropin release was accompanied by a slight increase in ovarian growth as evidenced by the increase in gonadosomatic index. It appears that the stimulation of gonadotropin release by o,p'-DDT during early-recrudescence phase results in enhanced o varian growth. A comparable stimulatory effect was observed with estradiol-17 beta treatment during early- and late-recrudescence phases of the ovarian cycle using three injections on alternate days and slow release silastic implants (five days). The present study provides the first evidence for an estrogen-like action of o,p'-DDT on gonadotropin release in a teleost model. (C) 1998 Elsevier Science Ltd. All rights reserved.