HOMEORHETIC ACTIONS ON TISSUE PROTEIN-METABOLISM AFTER THE ADMINISTRATION OF RAT GROWTH-HORMONE TO NORMAL RATS

An acute treatment with rat growth hormone (1 mug/g) to intact female rats produced immediate changes in muscle and bone protein synthesis as well as in muscle protein breakdown, while glucose and glutamate-piruvate transaminase plasma levels were not altered. These effects, apparently, are not mediated by systemic insulin-like growth factor I. Also a long-term treatment with somatotropin (0.1 mug/g/d) for 22 days was performed, in which protein synthesis rates in muscle, liver and bone remained unchanged. However, the growth hormone long-term treatment induced a decrease in muscle proteolytic activity and an increase in tibia weight. In this context, this experiment describes, apparently for the first time, the systemic effect of growth hormone in entire female rats. Data suggest that a single dose of rat growth hormone produces immediate changes in tissue protein metabolism, through a direct effect of growth hormone. These effects were not observed after the long-term growth hormone treatment, although these animals showed an increased in tibia proportions.