BASAL SECRETORY ACTIVITY OF THE HYPOTHALAMO-PITUITARY-ADRENOCORTICAL AXIS IS ENHANCED IN HEALTHY ELDERLY - AN ASSESSMENT DURING UNDISTURBED NIGHTTIME SLEEP

The process of aging is characterized by a disturbed neuroendocrine regulation, including a changed secretory activity of the hypothalamo-pituitary-adrenocortical (HPA) axis. In the present study adrenocorticotropin (ACTH) and cortisol secretion was monitored during nocturnal sleep (controlled by somnopolygraphy) in healthy aged men (N = 10, age range 70-92 years, mean 78.2 years) and women (N = 10, age range 70-88 years, mean 78.6 years), and in young male controls (N = 16, age range 20-34 years, mean 24.9 years). Blood was drawn every 15 min. Mast important, basal HPA secretary activity was enhanced distinctly in the elderly, as indicated by significantly elevated nadirs of plasma cortisol and ACTH concentrations occurring during early nocturnal sleep (p < 0.001, compared to young controls) and by elevated average levels of cortisol and ACTH between 23.00 and 03.00 h (p < 0.001). The first rise in nocturnal plasma cortisol began, on average, 67 min earlier than in young controls (p < 0.005). Changes of endocrine activity were associated with marked reductions of slow-wave sleep (SWS, p < 0.05) and rapid eye movement (REM) sleep in the elderly (p < 0.01), while time awake and in stage I sleep was increased. The REM sleep coincided with decreased HPA secretory activity, irrespective of age, indicating that the link between the ultradian sleep structure and the secretory HPA activity is maintained in the elderly. It is concluded that the age-related elevation of basal HPA secretory activity is of central nervous origin, leading to a phase advance of the circadian pacemaker and an elevation of the basal secretory rate of the HPA axis. Considering complementary results from animal studies, it is suggested that basal HPA hypersecretion associated with SWS deficits in the elderly are markers for an altered function of hippocampal corticosteroid receptors which are involved in the tonic inhibition of HPA secretory activity.