ESTRADIOL-17-BETA AND O,P'-DDT STIMULATE GONADOTROPIN-RELEASE IN ATLANTIC CROAKER

Xenobiotic estrogens have the potential to act at a variety of estroge n-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 neuroendocr ine 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 go nadal recrudescence phase, The o,p'-DDT exposure elicited a significan t increase in plasma gonadotropin levels after both 3 and 7 weeks of e xposure. The stimulatory effect of o,p'-DDT on basal (spontaneous) gon adotropin release was accompanied by a slight increase in ovarian grow th as evidenced by the increase in gonadosomatic index. It appears tha t the stimulation of gonadotropin release by o,p'-DDT during early-rec rudescence phase results in enhanced o varian growth. A comparable sti mulatory effect was observed with estradiol-17 beta treatment during e arly- and late-recrudescence phases of the ovarian cycle using three i njections on alternate days and slow release silastic implants (five d ays). The present study provides the first evidence for an estrogen-li ke action of o,p'-DDT on gonadotropin release in a teleost model. (C) 1998 Elsevier Science Ltd. All rights reserved.