STUDIES ON ROLE OF CATECHOLAMINES AS REGULATORS OF TYROSINE AMINOTRANSFERASE

It has been suggested that catecholamines are involved in the control of tyrosine aminotransferase activity. We have studied the effects of drugs which produce adrenergic blockade and catecholamine depletion on the activity of tyrosine aminotransferase (TAT) in rat liver. Phentolamine was found to increase TAT activity while phenoxybenzamine and propranolol had no effect. Of the depleting agents tested reserpine, guanethidine and α-methyl-para-tyrosine increased TAT activity while α-methyl-meta-tyrosine had no effect. All compounds which increased TAT activity also increase the plasma corticosterone concentration; α-methyl-para-tyrosine also increased slightly the enzyme activity in adrenalectomized rats. Thus, TAT activity is influenced by the changes in plasma corticosterone levels which these compounds produced, rather than their adrenergic blocking or catecholamine depleting effects. The response to α-methyl-para-tyrosine in adrenalectomized animals suggests that some additional mechanism is also involved. © 1969.