Simultaneous determination of cortisol, deoxycortisol and corticosterone in plasma and urine by competitive protein binding assay. Response of normal subjects to ACTH and metyrapone

A procedure is described for measurement of Cortisol, deoxycortisol and corticosterone in samples of plasma or urine by competitive protein binding assay. The method, involving t.l.c., is such that no “blank” value is dealt with; amounts as small as 1 ng of cortisol and 0–15 ng of deoxycortisol and corticosteronecan be reliably measured. It is therefore suitable for clinical and investigative purposes.In healthy adults the plasma levels at 9 a.m. are 16.1 μg/100 ml for cortisol, 0.11 μg/10ml for deoxycortisol and 0.70 μg/100 ml for corticosterone. The urinary excretion of unconjugated cortisol, deoxycortisol and corticosterone are respectively 34.0, 0.31 and 2.04 μg/24 h. At the end of an ACTH infusion (0.25 mg i.v. over 8 h) the plasma levels of cortisol had risen to 48.1 μg/100 ml and those of deoxycortisol and corticosterone to 0.34 and 5.90 μg/100 ml, respectively. The corresponding values for urinary excretion of unconjugated cortisol, deoxycortisol and corticosterone were 1320, 2.0 and 23.0 μg/24 h. Oral administration of metyrapone, 750 mg q. 4h, for 48 h, induces a fall of plasma cortisol to 3.6 μg/100 ml while plasma deoxycortisol level increases to 16 μg/100 ml; concomitantly urinary excretion of unconjugated cortisol decreases to 14.3 μg/24 h and that of unconjugated deoxycortisol rises to 24.8 μg/24 h, while plasma and urine corticosterone levels are left unaffected.