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The Effect of Glucocorticoids on the Relative Distribution of Aspartate Aminotransferase Isozymes of Morris Hepatoma 5123B

Laboratory of Biochemistry, National Cancer Institute, NIH, USPHS, Department of Health, Education, and Welfare, Bethesda, Maryland 20014

The effect of adrenal glucocorticoids on the activity and on the relative isozyme distribution of aspartate aminotransferase from normal liver and from Hepatoma 5123B (Morris) under a defined set of conditions was studied.

Although no marked effect was observed on the specific activities and on the relative isozyme distribution of the aspartate aminotransferase from normal female rat liver after adrenalectomy, hydrocortisone treatment, or both, there appeared to be some responsiveness by aspartate aminotransferase of Hepatoma 5123B to these treatments. Adrenalectomy effected a decrease in specific activity of the aspartate aminotransferase from Hepatoma 5123B, while hydrocortisone caused a slight increase in specific activity, as well as a change in the isozyme distribution in favor of the cationic or mitochondrial component. A combination of adrenalectomy and hydrocortisone treatment caused a normalization of the two effects on the specific activity and an alteration of the isozyme distribution favoring the cationic component.

Under the conditions of these experiments, the specific activity of the aspartate aminotransferase from normal male rat liver remained essentially unchanged upon administration of cortisone. However, adrenalectomy of the tumor-bearing male animal caused a decrease, and cortisone administration, a slight increase in specific activity of the tumor aspartate aminotransferase. Cortisone or hydrocortisone administration to adrenalectomized male tumor-bearing rats neither normalized the decrease in tumor aspartate aminotransferase activity caused by the adrenalectomy nor caused an alteration in the isozyme profile.

Received 9/19/67. Accepted 6/24/68.