RADIOIMMUNOASSAY OF 18-HYDROXY-11-DEOXYCORTICOSTERONE IN PLASMA

A method is described for the radioimmunoassay of 18-OH-DOC [deoxycorticosterone] using antibodies generated in rabbits against the carboxymethoxime derivative coupled to bovine serum albumin. The procedure uses 4 ml of plasma with intra- and inter-assay variations of 8 and 9%, respectively. Standard 18-OH-DOC added to plasma from an adrenalectomized patient gave a regression equation, Y = 0.974 X .+-. 2.210 and a correlation coefficient of 0.999. The only cross reacting steroid, 18-OH-corticosterone, which may lead to falsely high levels, is removed by a single TLC step. Blood levels in normal subjects agree closely with those calculated indirectly by metabolic clearance and secretion rate measurements. ACTH stimulation produced an 18-fold increase in plasma concentration while dexamethasone suppression decreased levels 3-fold. Four hours in the upright position resulted in a decreased plasma concentration while aldosterone increased. No significant response to dietary Na restriction could be demonstrated.