Cortisone-provoked depression of plasma tyrosine concentration: relation to enzyme induction in man.

Open Access
Publisher Website
Google Scholar
Abstract
Despite extensive studies of alterations in the activity of tyrosine transaminase in animals, only limited attention has been paid to the possible existence of steroid-inducible enzymes in man. In the present report, the administration of cortisone to euthyroid and hypo-thyroid adult human subjects in divided doses for 1 and 2 days was shown to produce consistent decreases of several Mg/ml in the concentration of tyrosine in plasma after an overnight fast. Cortisone also decreased the plasma levels of tyrosine 3 hrs. after an oral load of tyrosine had been fed, compared to results obtained after oral loading before cortisone administration. In hyperthyroid subjects, by contrast, cortisone produced no consistent changes in either the levels of tyrosine in fasting subjects, or the levels in plasma 3 hr. after an oral load of tyrosine. The results are consistent with the hypothesis that cortisone depresses the concentration of tyrosine in plasma by increasing the activity of hepatic tyrosine transaminase. This process of enzyme induction appears to be modified in hyperthyroid subjects in a manner entirely analogous to that previously described in experimental animals. Thyroid and adrenal cortical hormones differ markedly in their effects upon the metabolism of tyrosine, with respect to the plasma levels of tyrosine, and the activity of hepatic tyrosine transaminase.