Regulation of 18-hydroxydeoxycorticosterone in the rat

Simultaneous measurements of plasma 18-hydroxydeoxycorticosterone (18 OH-DOC), corticosterone, and aldosterone were performed in the rat by using RIA. Under basal conditions, 18 OH-DOC levels averaged 11.3 +/- 3.7 (SE) ng/ml. Plasma concentrations were increased 8-fold (86.8 +/- 8.0 ng/ml) 1 h after 1 U sc ACTH. Dexamethasone suppressed 18 OH-DOC to less than 1.5 ng/ml, irrespective of Na+ intake. Neither Na+ depletion nor Na+ loading had any influence on 18 OH-DOC levels. Excellent correlation between 18 OH-DOC and corticosterone (r = 0.90, P less than 0.001) was observed, whereas there was none between 18 OH-DOC and aldosterone (r = 0.061, P greater than 0.6). In the rat, 18 OH-DOC is an ACTH-dependent steroid which does not appear to be under the influence of the renin-angiotensin system.