REDUCED EPINEPHRINE CLEARANCE AND GLYCEMIC SENSITIVITY TO EPINEPHRINEIN OLDER INDIVIDUALS

To test the hypothesis that glycemic sensitivity to pinephrine is redu ced in older individuals and to assess the impact of a sedentary lifes tyle on responses to the hormone, we performed 30-min sequential intra venous infusions of epinephrine (0, 41, 82, 164, 246, and 328 pmol.kg( -1).min(-1)) in young (n = 10) and older (n = 23) healthy subjects. We performed these again after 12 mo of physical training, which raised peak O-2 consumption from 24.4 +/- 1.0 to 30.4 +/- 1.4 ml.kg(-1).min(- 1) (P < 0.01) in most of the older subjects (n = 21). During epinephri ne infusions, plasma epinephrine concentrations were higher (P = 0.000 1) in older than in young subjects (e.g., final values of 7,280 +/- 50 0 vs. 4,560 +/- 380 pmol/l, respectively), indicating that the clearan ce of epinephrine from the circulation was reduced in the older indivi duals. Plasma epinephrine concentration-response curves disclosed redu ced glycemic sensitivity to the hormone in the older subjects (P = 0.0 001), a finding plausibly attributed to increased sympathetic neural a ctivity, as evidenced here by higher plasma norepinephrine concentrati ons (P = 0.0001) in the alder subjects and consequent desensitization of cellular responsiveness to catecholamines. Training did not correct reduced epinephrine clearance, reduced glycemic sensitivity to epinep hrine, or raised norepinephrine levels. We conclude that aging is asso ciated with reduced clearance of epinephrine from the circulation and reduced glycemic sensitivity to epinephrine, the latter plausibly attr ibuted to an age-associated increase in sympathetic neural norepinephr ine release. These age-associated changes are not the result of a sede ntary lifestyle.