PLASMA BETA-ENDORPHIN, CORTISOL AND NOREPINEPHRINE RESPONSES TO PHYSICAL AND METABOLIC STRESSORS IN YOUNG AND ELDERLY HUMANS

The aim of the present study was to evaluate the effects of ageing on the activity of both the hypothalamic pituitary-adrenal axis and the sympathetic system in response to physical and metabolic stimuli. Eight young and eight elderly healthy subjects were studied. Three different tests were performed: handgrip, cold pressor and insulin-induced hypoglycaemia. Plasma beta-endorphin (beta-END), cortisol and norepinephrine (NEpi) levels were measured before and during the tests. While the two physical tests, handgrip and cold pressor, did not induce significant changes in plasma beta-END and cortisol levels, plasma NEpi levels rose in both young and aged subjects. The response of plasma NEpi was significantly higher in elderly than in young men. During the insulin-induced hypoglycaemia, plasma beta-END, cortisol and NEpi values significantly increased in both young and elderly men, the group of elderly subjects showing an enhanced responsiveness of plasma NEpi levels. These data suggest that ageing is associated with an increased activity of the sympathetic system and a normal responsiveness of the hypothalamic-pituitary-adrenal axis to the hypoglycaemic stress.