THE EFFECTS OF NORMAL AGING ON CORTISOL AND ADRENOCORTICOTROPIN RESPONSES TO HYPERTONIC SALINE INFUSION

To assess the effects of aging on hypothalamic-pituitary-adrenal (HPA) axis responsivity, we compared the plasma cortisol and adrenocorticot ropin (ACTH) responses to hypertonic saline infusion between normal ol der and young human volunteers. We administered a 90 min hypertonic sa line infusion (5% sodium chloride at 0.06 ml/kg/min) and a 90 min plac ebo infusion (0.9% sodium chloride at 0.06 ml/kg/min) to normal young subjects (n=13, age=29 +/- 2 years) and normal older subjects (n=8, ag e=63 +/- 3 years). Plasma cortisol, ACTH, osmolality and arginine vaso pressin (AVP) were measured before and at 30 min intervals during the infusions. The rate of increase in plasma osmolality and AVP induced b y hypertonic saline infusion was similar between groups. The plasma co rtisol increase during hypertonic saline infusion was greater in norma l older subjects than in young subjects (p=.03), but a stimulatory eff ect of hypertonic saline infusion on plasma ACTH was not apparent in e ither older or young subjects. These results suggest increased sensiti vity with human aging to stimulation of cortisol release by hypertonic saline infusion at the adrenocortical level of the HPA axis.