Radioimmunoassay for Urinary Free 19-Nor-Deoxycorticosterone: Effects of Adrenocorticotropin and Sodium Depletion*

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Abstract
A RIA for urinary free deoxycorticosterone (DOC) and 19-nor-deoxycorticosterone [21-hydroxy-19-nor-4- pregnene-3,20-dione (19-nor-DOC)] was developed and used to measure urinary free DOC and 19-nor-DOC in rats kept on normal and low sodium diets and before and after ACTH administration. The RIA required a preliminary high performance liquid chromatography purification using a Lichrosorb diol column before the eluates were assayed using highly specific antibodies. The intraassay variability was 9.8% for DOC and 10% for 19-nor-DOC; the interassay variabilities were 19% and 16%, respectively. Urinary free DOC excretion was 0.71 ± 0.15 ng/day (mean ± SD) in rats maintained on a normal sodium diet and 1.42 ± 0.46 ng/day after 3 days of a sodium-restricted diet. Urinary free 19- nor-DOC was 10.5 ± 5.5 ng/day in rats kept on the normal sodium diet and 28.6 ± 11.5 ng/dl after 3 days of a sodiumrestricted diet. ACTH increased the excretion of urinary free DOC from 0.72 ± 0.2 to 4.62 ± 2.3 ng/day and that of 19-nor-DOC from 5.37 ± 2.8 to 10.15 ± 2.5 ng/day. These data indicate that the adrenal precursor of 19-nor-DOC probably comes from both the zona fasciculata and the glomerulosa to explain the ACTH and sodium depletion responses.