INTERACTION OF CADMIUM AND ESTRADIOL-17-BETA ON METALLOTHIONEIN AND VITELLOGENIN SYNTHESIS IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The induction of metallothionein and vitellogenin synthesis in rainbow trout liver was studied after injection of oestradiol-17 beta alone o r in combination with cadmium or zinc. Intraperitoneal injection of oe stradiol-17 beta increased the liver somatic index, with subsequent in duction of vitellogenin synthesis. Oestradiol-17 beta did not induce m etallothionein synthesis. Injection of cadmium induced the synthesis o f metallothionein mRNA and metallothionein. Injection of oestradiol-17 beta in combination with cadmium resulted in inhibition of transcript ion and translation of both vitellogenin and metallothionein. Chromato graphy of liver cytosols revealed that cadmium, when co-injected with oestradiol-17 beta, did not bind to metallothionein but would initiall y bind to high-molecular-mass (HM(r)) cytosolic proteins. In fish inje cted with cadmium in combination with oestradiol-17 beta, cadmium was gradually redistributed from HM(r) proteins to metallothionein. This r esulted in induction of metallothionein synthesis and in binding of mo st of the cadmium to metallothionein. Induction of vitellogenin mRNA w as observed 15 days after injection, as cadmium was being redistribute d to newly synthesized metallothionein. These findings indicate that c admium inhibits the transcription of vitellogenin. The binding of cadm ium to these non-metallothionein proteins represses the induction of m etallothionein and results in increased toxicity of the metal. Preindu ction of metallothionein by zinc injections resulted in decreased cadm ium sensitivity of the fish and a decrease in the repression of vitell ogenin mRNA. Furthermore, a role for metallothionein in the detoxifica tion of cadmium is indicated by the induction of vitellogenin synthesi s that occurs once metallothionein has begun sequestering cadmium.