Role of 18-Hydroxylation in the Biosynthesis of Aldosterone12

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Abstract
The role of 18-hydroxylation in the biosynthesis of aldosterone from corticosterone was investigated by incubating radioactive 18-hydroxycorticosterone with aldosterone- producing adrenal tissue. Small, but significant, conversions were obtained which indicated that the 18-hydroxy derivative was a possible precursor. When corticosterone was incubated under identical conditions, however, the yields of aldosterone were 17 to 81 times greater. The variables in these experiments included the use of bullfrog, beef or human adrenals and the use of tissue slices as well as homogenates. A comparison of progesterone with its 18-hydroxy derivative and deoxycorticosterone with its 18-hydroxy derivative gave similar results. The 18-deoxy steroid was a more effective precursor of aldosterone than the corresponding 18-hydroxy derivative. The 18-hydroxy steroids in the incubation medium probably exist largely as 18,20-cyclic hemiketals. Their slower rate of conversion to aldosterone in vitro may be explained by the relative resistance toward oxidation of these cyclic forms rather than by the existence of an alternate biosynthetic pathway which does not require 18-hydroxylation. (Endocrinology76: 514,1965)