Early effects of glucocorticoid treatment on amino acid metabolism in lymphosarcoma P1798.

Administration of 9a-fluoroprednisolone causes an early (3 hr) decrease of basic amino acid incorporation into CS-P1798 lymphosarcoma protein. Decreased utilization of neutral amino acids is observed after 6 hr. These effects are accompanied by expansion of the intratumoral free amino acid pool in CS-but not in CR-P1798. Thus, decreased incorporation of radioactive amino acids in CS-P1798 appears to result from pool dilution of the tracers. It is suggested that the increase in intratumoral levels of free amino acids is a consequence of steroid-induced breakdown of tumor protein and that this effect may be related to tumor regression.