Circadian time structure in the endocrine system of elderly subjects.

Six young, healthy males (mean age 27 +/- 0.8 years) and six healthy elderly men (mean age 75 +/- 2.0 years) underwent an evaluation of their circadian rhythms in cortisol, PRL, and TSH; oral body temperature and heart rate also were recorded. In the two groups no differences in the circadian patterns of cortisol, PRL, and body temperature were found. We consider it remarkable that the mesor of PRL values did not differ significantly between young and elderly subjects. A markedly advanced TSH acrophase was found in the elderly compared to the young controls. This change in acrophase could be important, because the hormone is known to be a marker of the function of the hypothalamus-hypophysis axis. In addition, an advance of the acrophase of the heart rate in the elderly compared to the younger age group was observed.