[Diurnal and seasonal variations in the plasma levels of cortisol and its precursors in Macaca mulatta].

The presence of circadian and seasonal rhythms of cortisol, 11-desoxycortisol, 17 alpha-hydroxyprogesterone and 17 alpha-hydroxypregnenolone in the blood plasma of rhesus monkeys was found by the radioimmunological technique. The circadian rhythm was characterized by the highest content of all the steroids early in the morning followed by its decrease to the minimum in the late evening. The time-course of the precursor content was in good agreement with the hormonal level throughout 24 hours. The circadian rhythm pattern did not depend on the season, though the average diurnal concentrations varied considerably, being the highest in spring. Possible mechanisms of circadian and seasonal rhythms of the adrenal gland activity are discussed.