Abstract

The circadian rhythms of plasma cortisol was examined in 25 persons aged between 70 and 100 years by comparison with 5 adults aged between 17 and 38 years. The blood samples were drawn at 16 hundred, 20 hundred, 00 hundred, 04 hundred and 08 hundred hrs. Cortisol was assayed by the fluorimetric method. The experimental data were analyzed by Halberg's mean-cosinor method. The results showed that the circadian rhythm in plasma cortisol changes with age. The characteristic phenomena found were the following: a tendency towards reducing the hourly quantitative differences, comparatively more marked between 90 and 100 years; anticipation of the cortisol maximum level of 08 hundred at 04 hundred hrs in the group of 71 to 80 years, and at 00 hundred hrs in some of the subjects older than 80. A normal circadian rhythm was found in 2 of the 25 cases examined. These changes imply variations of the same kind in the CRF and ACTH levels. The changes in the circadian rhythms of cortisol show that the regulation systems are also implied in the aging process. It is possible that early-morning insomnia of the aged be due to this anticipation in cortisol secretion.