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ABSTRACT The diurnal variation in plasma cortisol, corticosterone and non-protein-bound cortisol was investigated using altogether 991 plasma samples obtained from preoperative chronically ill (control) subjects and patients during and following major surgery. A fluorimetric method using an elution chromatography on Amberlite IRC-50 and the equilibrium dialysis method were used for the determinations. The diurnal variation in plasma cortisol of the preoperative control subjects reached a peak (17.3 μg/100 ml) at 6 a.m. and declined to the lowest level (2.3 μg/100 ml) between 10 p.m. and midnight. The maximum value in the levels of corticosterone (0.6 μg/100 ml) was observed at 6 a.m. Surgery caused a steep rise in plasma cortisol showing a maximum value (30.0 μg/100 ml) 2 to 4 hours after the end of the operation. Although the average of the morning levels of plasma cortisol returned to the control levels within 4 to 5 days, the evening levels returned on the 6th day after the operation. The response of plasma corticosterone in the surgery group was found to parallel the change in plasma cortisol. However, the increase in the corticosterone concentration was significantly higher than that of cortisol. The percentage of non-protein-bound cortisol in the plasma of the preoperative control subjects was found to be 2.5 to 3.3 per cent at 6 and 8 a.m. and 1.5 per cent at midnight, while the percentage remained almost unchanged (about 2%) at 10 a.m., 12 a.m. and 6 p.m. The percentage increased significantly during and for 4 days following the operation, concomitant with the increase in the levels of plasma cortisol. It is suggested that stressful situations are associated with markedly increased plasma levels of biologically active cortisol.
HAMANAKA et al. (1970) studied this question.