DIFFERENTIAL SENSITIVITY OF ZONAGENESIS AND VITELLOGENESIS IN ATLANTIC SALMON (SALMO-SALAR L) TO DDT PESTICIDES

In Atlantic salmon (Salmo salar L) female sexual maturation entails bo th zonagenesis and vitellogenesis, both of which are controlled by inc reasing levels of estradiol-17 beta (E-2). Antibodies against salmon z ona radiata proteins (eggshell zr-proteins) and vitellogenin were used to monitor induction of oogenesis in juvenile salmon. Molecular weigh ts of zr-monomers were estimated to about 66, 61, and 55 kDa, and to a bout 180 kDa for vitellogenin. Xenobiotics such as the pesticide DDT i mpair biological reproduction. The o,p'-DDT hloro-2-[2-chlorophenyl]-2 -[4-chlorophenyl]ethane) isomer seems to be a xenoestrogen. Serum leve ls of zr-proteins and vitellogenin, and hepatocytic biosynthesis of th ese components, were determined after in vivo treatment of salmon with DDT (technical, p'-(1,1,1-trichloro-2,2-bis[4-chlorophenyl]ethane) or o,p'-DDT) or E-2. Exposing fish to frequent doses of o,p'-DDT (25 mg/ kg b.w. (body weight) twice a week, six times totally) resulted in ind uction of all three zr-protein monomers, but not of vitellogenin. In c ontrast, three weekly injection of 10 mg/kg b.w of either of the three DDT preparations did not induce typical zr-proteins or vitellogenin i n serum. In vivo studies with combined DDT + E-2 injections showed tha t none of the DDT preparations influenced E-2-induced biosynthesis of zr-proteins or vitellogenin. E-2 induction of these oogenetic processe s was not blocked even by a high concentration (125 mg/kg b.w.) of o,p '-DDT. Furthermore, pretreatment of salmon with o,p'-DDT for 2 weeks, followed by one injection of E-2, did not antagonize biosynthesis of z r-proteins, but serum concentration of vitellogenin was decreased. The data indicate that in juvenile salmon o,p'-DDT may be xenoestrogenic with regard to zonagenesis, but weakly anti-(xeno)estrogenic with rega rd to vitellogenesis. These findings suggest new complexities in fish reproductive toxicology of xenoestrogens. Compared to vitellogenesis, zonagenesis is a more sensitive parameter for monitoring reproductive effects of xenoestrogens. J. Exp. Zool. 281:346-353, 1998. (C) 1998 Wi ley-Liss, Inc.