Corticosteroid side chain oxidations--II. Metabolism of 20-dihydro steroids and evidence for steroid acid formation by direct oxidation at C-21.

Rabbits have been injected with 4-14C-labelled progesterone, deoxycorticosterone and corticosterone and the corresponding 20 beta-3H-reduced steroids (20-dihydro steroids) in order to compare the influence of oxidation at C-20 on the excretion of steroid acids. Both 20 beta-reduced progesterone and deoxycorticosterone were extensively oxidized at C-20 and metabolized to 20-oxo-21-oic acids devoid of tritium. A small proportion of the acidic metabolites of [20 beta-3H]dihydro deoxycorticosterone retained tritium. By contrast the majority of the metabolites of [20 beta-3H]dihydro corticosterone were tritiated and [11 beta,20 beta-3H]-dihydroxy-4-pregnene-3-one-21-oic acid was identified as a major acidic metabolite. These results indicate that the presence of a 11 beta-hydroxyl in 20 beta-dihydro corticosterone inhibits oxidation at C-20 and provides evidence for the direct oxidation of this corticosteroid at C-21 in this species.