Quantitative relationship between adrenal cytochrome P-450 and its reducing system, and their organ specificities in relation to corticoidogenesis

Adrenocortical factors in hypertension. I. Significance of 18-hydroxy-11-deoxycorticosterone

Low renin essential hypertension and the syndrome of mineralocorticoid excess have two features in common, low plasma renin activity and volume-sensitive hypertension. The proposal that both disorders share a common mechanism--because of the ability of agents that inhibit or antagonize the adrenocortical secretion to lower blood pressure in the low renin hypertensive group--appears to be based on a circular argument. The beneficial effect of removal or neutralization of the adrenocortical contribution only constitutes evidence for volume-dependency or sensitivity, which is how the low renin group is defined. Any measure that blocks a component of the normal homeostatic chain for the maintenance of extracellular and intravascular volume including the adrenal cortex would be expected to have a beneficial effect in volume-sensitive hypertension. Evidence for an adrenal factor in low renin hypertension must rest on the isolation of an active substance that reproduces the effect when readministered. 18-Hydroxy-11-deoxycorticosterone (18-OH-DOC) does not meet these criteria. It is not significantly increased in experimental hypertension and, although its overproduction in unselected low renin essential hypertensive patients remains controversial, the magnitude of the reported elevations is insufficient in relation to the low biologic activity of the steroid to account for a significant effect. Apart from its increase in the 17alpha-hydroxylase defect, 18-OH-DOC is increased in primary aldosteronism and may also be an indicator of a histologic variant of the aldosteronoma. On the basis of a large body of evidence showing parallelism between the 11beta- and 18-hydroxylase functions of the fasciculata zone, we have proposed that both enzymic functions are functionally related and may involve the same enzyme protein and catalytic site. According to this view, the secretion of 18-OH-DOC would have no special significance of its own but would be an obligatory consequence of the secretion of fasciculata zone corticosterone.