[Effect of somatotropin on cathepsin D in the liver of hypo- and hyperthyroid rats]

In experiments on albino male rats the dependence of the cathepsin D activity on the thyroid hormone- and somatotropin levels in the organism was studied. It was demonstrated that the total cathepsin D activity in the liver of hypothyroid rats is lowered by 37% and that of hyperthyroid animals is augmented by 63%. Somatotropin injected to intact rats within 10 days in doses of 0.5 mg/100 g body weight enhanced the total enzyme activity by 19%. Hormone injection to hypothyroid animals returns to the normal cathepsin D activity, whereas in hyperthyroid rats the enzyme effect is significantly lowered under hormone action. Protein content in the nucleus-free homogenate of the hypothyroid rat liver does not differ from that of intact rats and is increased by 27% in hyperthyroid animals. Exogenous somatotropin returns to normal protein content in hyperthyroid rats.