Depression of Alanine Transaminase Activity in the Liver

responsive to changes in the balance between protein anabolism and catabolism. The activity of this enzyme is low when conservation of protein is required for body growth. Thus, in the livers of immature rats, alanine transaminase is only one-fourth the level of that found in adult rat liver (11). Conversely, alanine transaminase activity in liver may be elevated by as much as sevenfold when gluconeogenesis and catabolism of protein are increased by treatment with glucocorticoids (5, 34) or by withholding food (34). Furthermore, treatment of rats bearing Walker carcinoma 256 with cortisol or by feeding a 75 per cent casein diet will also inhibit the growth of the tumor and enhance the activity of this transaminase in tumor tissue (32). The capacity of the Walker tumor to utilize large amounts of protein at the expense of the host has been studied extensively (13). The results of the experiments described in this paper indicate that, as the amount of protein available to the host becomes limiting during the growth of the tumor, the level of alanine transaminase in liver is reduced and this enzyme becomes less responsive to cortisol.