Journal of Applied Physiology, Vol 78, Issue 1 172-178, Copyright © 1995 by American Physiological Society

ARTICLES

Effect of aging on beta 2-adrenergic receptor-stimulated flux of K+, PO4, FFA, and glycerol in human forearms

G. A. Ford, W. D. Dachman, T. F. Blaschke and B. B. Hoffman
Department of Medicine, Stanford University School of Medicine 94305.

beta-Adrenergic responses have been shown to decline with aging, particularly in the cardiovascular system. We infused terbutaline, a selective 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. Forearm K+, PO4, free fatty acid (FFA), and glycerol uptake were determined by measurement of forearm blood flow (using dye dilution) and brachial arterial and deep venous plasma substrate concentrations. Elderly subjects were less sensitive to terbutaline-mediated increases in forearm 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 the terbutaline concentration, a measure of forearm beta-adrenergic sensitivity, 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 glycerol 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 groups. Terbutaline-stimulated vasodilation and net glycerol efflux but not FFA efflux were impaired with aging. These data demonstrate that heterogeneous changes in beta-adrenergic responses occur with aging.

This article has been cited by other articles:

				A. J. Donato, L. A. Lesniewski, and M. D. Delp Ageing and exercise training alter adrenergic vasomotor responses of rat skeletal muscle arterioles J. Physiol., February 15, 2007; 579(1): 115 - 125. [Abstract] [Full Text] [PDF]

				T. CLAUSEN Na+-K+ Pump Regulation and Skeletal Muscle Contractility Physiol Rev, October 1, 2003; 83(4): 1269 - 1324. [Abstract] [Full Text] [PDF]

				H. Bundgaard, K. Kjeldsen, K. Suarez Krabbe, G. van Hall, L. Simonsen, J. Qvist, C. Muff Hansen, K. Moller, L. Fonsmark, P. Lav Madsen, et al. Endotoxemia stimulates skeletal muscle Na+-K+-ATPase and raises blood lactate under aerobic conditions in humans Am J Physiol Heart Circ Physiol, March 1, 2003; 284(3): H1028 - H1034. [Abstract] [Full Text] [PDF]

				O. M. Sejersted and G. Sjogaard Dynamics and Consequences of Potassium Shifts in Skeletal Muscle and Heart During Exercise Physiol Rev, October 1, 2000; 80(4): 1411 - 1481. [Abstract] [Full Text] [PDF]

				E. E. Blaak, M. A. van Baak, and W. H. M. Saris {beta}-Adrenergically Stimulated Fat Oxidation Is Diminished in Middle-Aged Compared to Young Subjects J. Clin. Endocrinol. Metab., October 1, 1999; 84(10): 3764 - 3769. [Abstract] [Full Text] [PDF]

				X. Sun, M. Nagarajan, P. W. Beesley, and Y.-C. Ng Age-associated differential expression of Na+-K+-ATPase subunit isoforms in skeletal muscles of F-344/BN rats J Appl Physiol, September 1, 1999; 87(3): 1132 - 1140. [Abstract] [Full Text] [PDF]

				J. E. Baumgardner, D. Baranov, D. S. Smith, and E. L. Zager The Effectiveness of Rapidly Infused Intravenous Fluids for Inducing Moderate Hypothermia in Neurosurgical Patients Anesth. Analg., July 1, 1999; 89(1): 163 - 163. [Abstract] [Full Text] [PDF]