Metyrapone modulation of tyrosine aminotransferase induction by dexamethasone in cultured hepatocytes.

Metyrapone, an inhibitor of cytochrome P-450-dependent monooxygenases, enhanced the induction of tyrosine aminotransferase by dexamethasone in primary cultures of hepatocytes, while it had no effect on the basal level of the enzyme activity in the absence of the hormone. The amplification of the hormonal induction of tyrosine aminotransferase activity was strictly correlated with the concentration and with the inhibitory action of the compound on cytochrome P-450. The phenomenon occurred even at the maximally effective concentrations of dexamethasone, thus showing that metyrapone is a 'Glucocorticoid Potency Amplifier'. The dexamethasone activity amplification by metyrapone could be the consequence of a modulation of the glucocorticoid biotransformations due to the cytochrome P-450 inhibitor.