Effects of o,p′-DDE, heptachlor, and 17β-estradiol on vitellogenin gene expression and the growth hormone/insulin-like growth factor-I axis in the tilapia, Oreochromis mossambicus

Effects of two endocrine disruptors, o,p'-DDE and heptachlor, and 17 beta-estradiol (EA on vitellogenin (Vg) and the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis were examined in male tilapia. In the first experiment, fish were given 5 weekly injections of either E-2, o,p'-DDE or heptachior (5 mu g/g). E-2 treatment increased plasma Vg and hepatic expression of three Vg genes (Vgs A, B. and C) and estrogen receptor alpha (ER alpha), while reducing plasma levels of IGF-I and Suppressing the expression of IGF-I, the GH receptor (GHR2) and the putative somatolactin receptor (GHR1). Neither pesticide greatly affected the other parameters examined, except for a significant reduction in expression of GHR2 and increased plasma IGF-I. In the second experiment, fish were given a single injection of o,p'-DDE or heptachlor (100 mu g/g), or E-2 (5 mu g/g) and sacrificed 5 days post-injection. Treatment with E2 Stimulated expression of all three Vg genes. Both o,p'-DDE and heptachlor increased expression of VgB, whereas only o,p'-DDE increased VgA expression. There was no effect of o,p'-DDE or heptachlor on VgC expression or plasma Vg levels. Treatment with o,p'-DDE and heptachlor as well as E-2 increased ER alpha and ER beta transcript levels. Similarly, both pesticides increased GHR1 and IGF-I expression, whereas no significant effect of E-2 was observed on GHR1, GHR2 or IGF-I expression. These results indicate that o,p'-DDE and heptachlor have varying temporal and dose effects on modulation of Vg and the GH/IGF-I axis that are distinct from E-2. (c) 2008 Elsevier Inc. All rights reserved.