Contrast analysis for the evaluation of the circadian rhythms of plasma cortisol, androstenedione, and testosterone in normal men and the possible influence of meals.

To evaluate the circadian rhythms of plasma androstenedione (delta) and testosterone (T), we used continuous blood withdrawal at 30-min intervals for 24 h to obtain integrated concentrations in six normal men. The data were submitted to contrast analysis as well as to a graphical method with smoothing of the variations between samples. As reference, cortisol (F) levels also were measured, since they have a well defined circadian rhythm. Integrated F concentrations had a circadian rhythm, with the highest levels between 0500 and 0900 h, nadir values between 2000 and 300 h, and secretory peaks coincident with lunch and dinner hours, suggesting the influence of food ingestion on secretion. Integrated androstenedione concentrations also had a circadian rhythm, with the highest levels between 0530 and 0930 h and the lowest between 1900 and 0230 h. There also were peaks with lunch and dinner, however, occurring some minutes before the corresponding ones for F. Integrated T concentrations had a circadian rhythm, with the peak values between 0100 and 1130 h and the lowest levels between 0700 and 2100 h. There were no peaks of the T integrated concentrations during the meal periods as found with F and delta. Furthermore, no correlation was found between the integrated concentrations of T and F or delta.