EFFECT OF AGING ON BETA(2)-ADRENERGIC RECEPTOR-STIMULATED FLUX OF K+,PO4, FFA, AND GLYCEROL IN HUMAN FOREARMS

beta-Adrenergic responses have been shown to decline with aging, parti cularly in the cardiovascular system. We infused terbutaline, a select ive beta(2)-adrenoceptor agonist, into the brachial artery of 10 young (mean age 25 yr, range 22-31 yr) and 9 elderly (mean age 73 yr, range 68-81 yr) healthy subjects to examine its effects on nutrient flux. F orearm K+, PO4, free fatty acid (FFA), and glycerol uptake were determ ined by measurement of forearm blood flow (using dye dilution) and bra chial arterial and deep venous plasma substrate concentrations. Elderl y subjects were less sensitive to terbutaline-mediated increases in fo rearm blood flow, net fluxes of K+, and glycerol but not net fluxes of FFA or PO4. The mean fitted slopes of each parameter vs. the log of t he terbutaline concentration, a measure of forearm beta-adrenergic sen sitivity, for young and elderly groups were 4.9 +/- 1.7 (SD) vs. 2.4 /- 2.3 for forearm blood flow (P < 0.05), 0.84 +/- 0.46 vs. 0.43 +/- 0 .37 for K+ net flux (P < 0.05), -157 +/- 113 vs. -26 +/- 26 for glycer ol net flux (P < 0.01), -336 +/- 429 vs. -44 +/- 457 for FFA net flux (P = 0.11), and 0.31 +/- 0.24 vs. 0.18 +/- 0.16 for PO4 net flux (P = 0.14). Terbutaline promoted net uptake of K+ into skeletal muscle less well in the elderly, although net PO4 flux was similar in the two gro ups. Terbutaline-stimulated vasodilation and net glycerol efflux but n ot FFA efflux were impaired with aging. These data demonstrate that he terogeneous changes in beta-adrenergic responses occur with aging.