It has been established in bovine capsule strippings, consisting mainly of zona glomerulosa tissue, that labeled progesterone, deoxycorticosterone and corticosterone are all converted to radioactive aldosterone. Analysis of the data indicates that at least 50 % of the aldosterone produced is derived from corticosterone; under certain conditions, with the addition of high concentrations of corticosterone, the percentage pathway is at least 92 % Progesterone studied at varying concentrations under similar conditions of incubation is a major precursor of both aldosterone and corticosterone; there is some possibility that aldosterone may be formed, to a minor extent, via a pathway not involving progesterone. Labeled deoxycorticosterone is also converted to aldosterone, and it seems likely, though not established by the present studies, that it is the intermediate between progesterone and corticosterone; thus the major sequence appears to be progesterone → deoxycorticosterone → corticosterone → aldosterone. Although the precursors of progesterone have not been demonstrated in incubations with capsule strippings, it has been found that homogenates prepared mainly from zone glomerulosa tissue can convert cholesterol to corticosterone and hence presumably to aldosterone. The route between cholesterol and corticosterone probably involves progesterone but this has not been established. The significance of these findings in relation to in vivo results has been briefly discussed.

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