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 adrenocorticotropin (ACTH) responses to hypertonic saline infusion between normal older and young human volunteers. We administered a 90 min hypertonic saline infusion (5% sodium chloride at 0.06 ml/kg/min) and a 90 min placebo 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, age = 63 +/- 3 years). Plasma cortisol, ACTH, osmolality and arginine vasopressin (AVP) were measured before and at 30 min intervals during the infusions. The rate of increase in plasma osmolality and AVP induced by hypertonic saline infusion was similar between groups. The plasma cortisol increase during hypertonic saline infusion was greater in normal older subjects than in young subjects (p = .03), but a stimulatory effect of hypertonic saline infusion on plasma ACTH was not apparent in either older or young subjects. These results suggest increased sensitivity with human aging to stimulation of cortisol release by hypertonic saline infusion at the adrenocortical level of the HPA axis.