A radioimmunoassay for tetrahydrocortisol.

A radioimmunoassay for urinary tetrahydrocortisol (THF) is described. Antibodies were produced in rabbits against a THF-monohemisuccinate:bovine serum albumin conjugate. The radioimmunoassay procedure involves enzymic hydrolysis of the urine, extraction with ethyl acetate, radioimmunoassay, and separation of free from bound steroid with Somogyi reagents. The antibody showed some cross-reaction with tetrahydro substance S (36%) which does not occur in urine in appreciable amounts and with tetrahydrocortisone (10%) which does. An analysis of monkey urine extracts before and after tlc purification revealed that the THF antibody was specific enough to permit assay of urines for THF during stress experiments without a purification step. THF values obtained correlated very highly with 17-hydroxycorticosteroid values on the same urines obtained from monkeys during a chair restraint experience (r = 0.97). Also for comparison purposes these same urines were assayed for free THF, total cortisol, and free cortisol. The free (unconjugated) steroids showed the greatest percentage increase over basal levels.