REGULATION OF METALLOTHIONEIN IN TELEOSTS - INDUCTION OF MTMRNA AND PROTEIN BY CADMIUM IN HEPATIC AND EXTRAHEPATIC TISSUES OF A MARINE FLATFISH, THE TURBOT (SCOPHTHALMUS-MAXIMUS)

Synthesis of the heavy metal-binding protein metallothionein (MT) was determined in the major organs of accumulation of Cd (liver, kidney an d gills) of a marine flatfish, the turbot, after intraperitoneal (i.p. ) administration of varying doses of Cd. Synthesis of MTmRNA and MT we re linearly related to dose only at low Cd dosages (up to ca. 100 mu g Cd/kg). Induction of MTmRNA was rapid, peaking 1-2 days after Cd admin istration in gills and kidneys, at 4 days in liver. In all three tissu es, at low doses of Cd, MTmRNA levels declined with an apparent half l ife of 5-7 days and for a given dose of Cd, similar MTmRNA concentrati ons were attained. Induction of MT levels temporally followed that of MTmRNA. Steady state levels of MT were attained more quickly at a low dose of Cd. At acute Cd doses of >200 mu gCd/kg, MT gene transcription and protein translation appeared to be progressively reduced, inferri ng that the rate of MT synthesis was limiting due to cytotoxicity of t he high acute Cd dosage. In contrast to MTmRNA levels which were induc ed to similar levels in the three tissues, MT levels decreased in the order liver > kidneys > gills implying differences in translational pr ocesses.