Transfer of metyrapone and its metabolite, rac-metyrapol, into breast milk.

Metyrapone, an inhibitor of corticosteroid biosynthesis, is used in the diagnosis and treatment of adrenocortical hyperfunction. The authors describe the excretion of metyrapone and its metabolite, rac-metyrapol, in milk from a lactating woman requiring metyrapone treatment (250 mg 4 times daily). At steady state, the average concentrations in milk and absolute and relative infant doses were 11 microg/L, 1.7 microg/kg/d, and 0.02%, respectively, for metyrapone, and 48.5 microg/L, 7.3 microg/kg/d, and 0.08%, respectively, for rac-metyrapol. The findings suggest that maternal metyrapone use during breastfeeding is extremely unlikely to be a significant risk for the breastfed infant.

Carbonyl reduction of metyrapone in human liver.

Carbonyl reduction was investigated in cytosolic and microsomal fractions of human liver using the ketone metyrapone as a substrate. The cytosolic enzyme has a stronger preference for NADPH over NADH than the microsomal enzyme: the former shows only 14% of the NADPH-supported activity while the latter exhibits 36% activity with NADH. Barbitone and quercitrin, the classic inhibitors of carbonyl reductases, do not affect metyrapone reduction in either fraction. Dicumarol and indomethacin, the specific inhibitors of NAD(P)H: quinone-oxidoreductase and dihydrodiol dehydrogenase, respectively, only slightly decreased metyrapol formation. In contrast, 5 alpha-dihydrotestosterone, the active form of the androgen steroid testosterone, inhibited metyrapone reduction very strongly in the microsomal fractions and is postulated to be the physiological substrate of the enzyme. This resembles the situation in mouse liver [E. Maser and K. J. Netter, Biochem Pharmacol 38: 3049-3054, 1989] where microsomal metyrapone reductase was inhibited by steroids and the purified enzyme was demonstrated to mediate androsterone oxidation. Immunoblot analysis revealed antigenic cross-reaction of antibodies against the 34 kDa metyrapone reductase from mouse liver microsomes with the homologous protein in human liver microsomes pointing to structural homologies between the respective enzymes of the two species. These results--together with previous findings, which have shown that there exist functional as well as structural relationships between microsomal mouse liver metyrapone reductase and 3 alpha-hydroxysteroid dehydrogenase from Pseudomonas testosteroni [E. Maser, U. Oppermann and K. J. Netter, Eur J Pharmacol 183:1366, 1990]--suggest that metyrapone reduction in human liver microsomes might be catalysed by a microsomal hydroxysteroid dehydrogenase.

Synthesis of N-oxide derivatives of metyrapone and their detection as in vitro metabolites.

A variety of possible N-oxidation products of 2-methyl-1, 2-bis(3-pyridyl)propan-1-one (metyrapone) have been synthesized by peracid oxidation, and characterized using various spectroscopic techniques. Specific and sensitive chromatographic techniques have been developed for the separation and identification of its in vitro metabolites. Incubation of metyrapone with rat or mouse hepatic microsomes, in the presence of a NADPH-regenerating system, leads to the formation of metyrapol (keto-reduction), and two mono-N-oxides.

Single dose metyrapone test: 11 beta-hydroxylase inhibition by metyrapone and reduced metyrapone assayed by radioimmunoassay.

To assess the effects of metyrapone and reduced metyrapone on 11 beta-hydroxylase inhibition, the plasma levels of cortisol, 11-deoxycortisol, and the inhibitors were measured by radioimmunoassays in 34 normal subjects 8 h after they received a single oral dose of metyrapone at midnight. The ratio of 11-deoxycortisol to cortisol, as an index of 11 beta-hydroxylase inhibition, was compared to plasma levels of metyrapone and reduced metyrapone. One subject received an infusion of metyrapone ditartrate in order to study the sequential conversion of metyrapone to reduced metyrapone. A new radioimmunoassay was developed for measurement of plasma concentrations of metyrapone and reduced metyrapone. Following intravenous administration of metyrapone, it is rapidly converted to an active metabolite, reduced metyrapone. At 8 h after a dose was given, the average reduced metyrapone level was 1.5 times higher than the average metyrapone level. Following oral administration of the drug, we found a high correlation when plasma levels of metyrapone were compared to reduced metyrapone and when the ratio of 11-deoxycortisol to cortisol was related to metyrapone or to total metyrapone levels. In conclusion, the conversion of metyrapone to reduced metyrapone is such that by 8 hours after a single oral dose, more than one-half of the inhibitory effect on 11 beta-hydroxylase appears to be produced by reduced metyrapone. The inhibitory action of metyrapone and reduced metyrapone on the enzyme system is reflected by their concentration in plasma.