Protein kinase activities were determined in liver from normal, thyroidectomized and triiodothyronine (T3)-treated rats. Changes related to thyroid hormone were observed in cytosol and nuclear protein kinase activities. When protamine was used as substrate for phosphorylation, thyroidectomy induced a decrease of protein kinase activity associated with nuclei but an increase of activity was found in the cytosol. Fifteen hours after injection of T3 the levels in nuclei and cytosol were restored to normal. When casein was used as substrate, hypothyroidism led to a lowering of protein kinase activity in both fractions and T3 treatment augmented the activity in both. These studies suggest that thyroid hormones modify hepatic protein kinase activity. Results differ depending upon the substrate used. The hormones also appear to alter the subcellular distribution of some protein kinase activities.
Phosphoprotamine phosphatase activity in the rat thyroid was examined by studying the release of inorganic phosphate from [32P]-phosphorylated protamine. Rats were given a normal diet supplemented or not with thyroxine (T4) (3 mg/l in 0.05% bovine serum albumin solution) or propylthiouracil (1 g/l in 1% sucrose solution) in drinking water for various periods. TSH was injected ip, 100 mU per animal. A significant increase of phosphatase specific activity-units per mg protein (3-fold) as well as units per gland- was observed following goitrogen treatment, whereas a decrease (50%) was seen in response to T4. Both the soluble and particle activities were similarly affected. As total activity decreased after T4 treatment, it appeared that only the Mn2+-stimulating enzyme was concerned, the Mn2+-unstimulated part remaining unaltered. In vitro cyclic AMP or cyclic GMP at concentrations from 10 micro M to 200 micro M had no effect on these phosphatase activities. TSH injected in chronically T4-treated rats (32 days treatment) failed to produce any significant enhancement in phosphatase activity whatever the time of injection before sacrifice (from 2 to 6 h). On the contrary a single injection of TSH in animals subjected to short treatment with T4 (2 days) induced an elevation of the enzyme activity, restoring partially the initial level. These findings suggest that TSH controls protein dephosphorylation activities in the thyroid. Furthermore, they offer additional evidence that prolonged T4 administration leads to decreased responsiveness to TSH.
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