Estrogenic activity of chlordecone, o,p'-DDT and o,p'-DDE in juvenile rainbow trout: Induction of vitellogenesis and interaction with hepatic estrogen binding sites

Persistent organochlorines such as chlordecone (CD), DDT, and DDT degradation products bioaccumulate in fish and potentially impair reproduction or development via estrogenic actions. We evaluated the estrogenicity of CD, o,p'-DDT, o,p'-DDE, and p,p'-DDE in juvenile rainbow trout by assessing their potential to induce vitellogenesis; estrogen-regulated hepatic synthesis of the yolk-protein precursor, vitellogenin (Vg). In order to compare the sensitivities of various markers of estrogen stimulation, trout were injected with 17 beta-estradiol (0-10 mg kg(-1)) on days 0 and 3 and were sampled on days 3-12. Estradiol (5 mg kg(-1)) increased plasma Vg (2400%; 640 mu g l(-1)), liver somatic index (200%) and hepatic cytosolic estrogen binding site levels (EBS, 300%) on day 6. These results suggested plasma Vg was the most sensitive marker of estrogen exposure. Chronic dietary exposure to CD (0.4 mg kg(-1) day(-1), 33 weeks) elevated plasma Vg (0.9 mu g l(-1)), but not hepatic EBS concentrations, and resulted in relatively high hepatic CD concentrations (16 mu g g(-1)). The in vivo estrogenicity of DDT was examined by injecting trout at 14 day intervals with single or triplicate doses of o,p'-DDT, o,p'-DDE or p,p'-DDE (0, 5, 15 or 30 mg kg(-1)) and monitoring vitellogenesis 14 days after the final injection. Plasma Vg and hepatic EBS concentrations were significantly elevated by o,p'-DDT and o,p'-DDE (total dose 45 and 90 mg kg(-1); 23-24 mu g Vg l(-1)) but not p,p'-DDE. Target organ doses were estimated by conducting a disposition study in which trout were injected with three doses of [C-14]p,p'-DDE (30 mg kg(-1)), at 14 day intervals. Hepatic [C-14]p,p'-DDE equivalent concentrations, 14 days after the final injection, averaged 14 mu g g(-1). Additionally, we evaluated the relative affinity of CD and DDT or DDE for trout hepatic EBS utilizing in vitro competitive binding assays. CD had relatively low affinity (1000-fold less than moxestrol, a synthetic estradiol) for trout hepatic EBS, o,p'-DDT and o,p'-DDE, but not p,p'-DDE, also exhibited low EBS affinity (approximately 156 000-fold less than moxestrol). Collectively, these results indicated that CD, o,p'-DDT and o,p'-DDE were weakly estrogenic in juvenile trout.