Anterior pituitary: triiodothyronine and/or dexamethasone induced changes in protein formation in thyroidectomized...

Protein formation in the anterior pituitary was investigated in vitro in thyroidectomized (TX) and/or adrenalectomited (AX) rats treated with a single dose of 100 micrograms/100 g of 3,5,3'-triiodothyronine (T3) and/or with a single dose of 10 micrograms/100 g of dexamethazone (DEX) 12 h before sacrifice. Male Wistar rats of a specific pathogen free colony 6 weeks after TX and/or AX receiving 1% calcium chloride and/or saline after surgery were used in the experiments. Non-pooled anterior pituitaries (in acellular condition) complemented with all essential amino acids, CPK, creatine phosphate in a HEPES buffer containing potassium acetate, magnesium acetate and dithiothreitol, were incubated with 35S-methionine at 28 degrees C for 10 or 40 min. The reaction was stopped by EDTA followed by RNAase plus DNAase treatment and the samples were analyzed for total 35S-methionine incorporation or by SDS 12.5% polyacrylamide gel slab electrophoresis (PAGE). As compared to intact rats (100%), TX and/or AX caused a significant diminution of the total 35S-methionine incorporation into protein ranging from 33% to 68% that may be easily restored to 107% by T3 plus DEX treatment. PAGE analysis reflects an appreciable relation between T3 administration and 21.5 kDa protein (growth hormone) formation in the anterior pituitary. In addition, the effect 5,5'-diphenylhydantoine (DPH) on 35S-methionine incorporation in relation to T3 nuclear specific binding was investigated. The data suggest that the decreased protein synthesis de novo is due to a significant diminution of T3 specific binding to nuclear receptors in the anterior pituitary.