Hepatic 15-hydroxylation of corticosteroids in the rat. Substrate specificity studied in the isolated perfused liver.

Abstract

The substrate specificity of a sex-specific hepatic 15-hydroxylase active on different C21O2 and C21O3 steroids was studied in the isolated perfused liver from female rats. Liquid-chromatographic separation methods in combination with computerized gas chromatography-mass spectrometry was employed to identify the metabolites formed. The majority (between 75-90%) of 15-hydroxylated compounds isolated were present as monosulphate conjugates while smaller amounts of disulphates were also detected. Hydroxylation was found to take place exclusively at position 15 beta. A certain number of 11-deoxy-21-hydroxy, 11-oxo-21-hydroxy and 11,21-dihydroxy steroids with a 3-keto-delta4-, 3-keto-5 alpha(5 beta)-, 3alpha, 5alpha- or 3 beta, 5 beta-structure were readily converted to 15 beta-hydroxylated metabolites. Depending on the structure of the substrate, between 20 and 87% of the total metabolites formed were 15 beta-hydroxylated. 5 alpha-Reduced steroids were better substrates for the hydroxylase than the corresponding 3-keto-delta4- or 5 beta-reduced compounds. The configuration of the hydroxylgroup at C-3 did not affect the degree of 15-hydroxylation. 11 beta-Hydroxylated steroids served as better substrates than the corresponding 11-dehydro-, 11-deoxy- or 11 alpha-hydroxy compounds. 5 alpha-Dihydrocorticosterone and 3 alpha, 5 alpha-tetrahydrocorticosterone were the best substrates for the 15 beta-hydroxylase.