Aminotransferase activities and involution of the thymus in rats bearing AH 130 tumors.

Involution of the thymus was observed in rats bearing AH 130 (solid-type) tumors. The thymus weight decreased with tumor growth. Daily injection of a pharmacological dose of hydrocortisone into normal rats resulted in involution of the thymus and marked increase in alanine aminotransferase activity. This treatment also caused slight increase in the activity of tyrosine aminotransferase but not of aspartate aminotransferase in these animals. Involution of the thymus in tumor-bearing rats, however, was not accompanied by appreciable increases in the activities of these aminotransferases, even at an advanced stage of tumor growth when the plasma corticosterone level was very high and significant increase in the activities of all these enzymes was observed in the liver. Further, additional injections of hydrocortisone into rats with tumors weighing more than 5% of the body weight did not cause any appreciable change in alanine aminotransferase activity in the thymus, although in rats with smaller tumors it slightly increased the enzyme activity in the thymus. Furthermore, in normal rats, increase in alanine aminotransferase activity in the thymus with involution of the glands was observed with a dose of corticosterone close to the physiological range attained in rats with tumors in an advanced stage.