ABSTRACT
This study tested the hypotheses that aging is associated with prolonged recovery after a challenge to the hypothalamic-pituitary-adrenal axis (acute exercise) and that aerobic fitness is associated with a blunting of the age-related loss of negative feedback sensitivity. Young (27 +/- 2.8 yr, n = 9), older (64.6 +/- 1.4 yr, n = 11), and older-fit women (66.3 +/- 2.2 yr, n = 11) underwent a short bout of treadmill exercise at high (but submaximal) intensity. The exercise trial elicited significant increases in heart rate, blood pressure, ACTH, and cortisol (P < 0.001). Although the young and the older women exhibited similar cortisol response to the trial and throughout the recovery period, the older women had a slower decrease of ACTH levels (P < 0.05), suggesting reduced negative feedback sensitivity with aging. Between the two groups of older women, the older-fit group had significantly greater rate of recovery of ACTH levels (P < 0.05) compared with the older unfit women. However, older fit women had greater cortisol production during the recovery period (P < 0.05), suggesting greater adrenal sensitivity to ACTH. These results suggest that aging is associated with changes in the dynamic function of the hypothalamic-pituitary-adrenal axis and that these changes are attenuated by aerobic fitness.
