Radioimmunoassay of tetrahydrocorticosterone (THB) in human urine

Antisera against tetrahydrocorticosterone (THB) (one of the metabolites of the glucocorticoid corticosterone) was raised in white New Zealand rabbits. A 3α,5β-THB-20-oxime-bovine serum albumin complex was used as antigen. The resulting titers were 1/300-1/19,000. The cross-reactions of the best antiserum were: THDOC 2.25%, THB-21-glucuronide 39%, and THF-21-glucuronide 4.8%. Other steroids and steroid metabolites have given negligible cross-reactions, e.g., allo-(3α,5α-)-THB 0.53%, tetrahydro-11-dehydro-corticosterone (THA) 0.92%, allo-THA 0%, and THB-3-glucuronide 0%. Two methods were introduced: for screening an estimation of THB-glucuronide, mostly THB-21-glucuronide ('THB-gluc.'), in unprocessed urine after simple dilution, and, specific estimation of THB using one paper chromatographic system. The values estimated by the first method showed a highly significant correlation (r = 0.9654, P < 0.01) with the values obtained by the second technique. Normal values (the second method) measured in subjects hospitalized under standardized conditions were: 21.8-177.6; mean 89.1 μg/24 hr. THB levels and 'THB-gluc.' levels react to ACTH stimulation and dexamethasone suppression and thus the authors propose that the methods are useful for the diagnosis of hyper- and hypocorticosterone production states.