Comparison Between the Effects of Aging on Antagonist and Agonist Interactions With Beta-Adrenergic Receptors on Human Mononuclear and Polymorphonuclear Leukocyte Membranes

Abstract

Age-related differences in the binding properties of beta-adrenergic receptors on lymphocyte membranes isolated from healthy individuals have been reported. The purpose of the present studies was to determine whether or not beta receptors on polymorphonuclear leukocyte (PMN) membranes showed similar age-related changes. Plasma Percoll gradients were used to isolate PMN and mononuclear leukocyte (MN) cells from blood drawn in the supine position from young (25-34 years) and elderly (60-76 years) healthy volunteers. Both blood pressures and plasma norepinephrine levels were significantly elevated in the elderly subjects. Saturation analysis with [125I]-(-) iodopindolol (IPIN) showed a 2.5-fold higher density of beta 2 receptors on the MN, but not PMN, membranes from the elderly. Neither the affinities of the receptor for IPIN or the agonist isoproterenol, nor the GTP-induced shift in agonist affinity, differed with subject age in either cell type. These results suggest that subpopulations of MN cells on which beta-adrenergic receptors are localized may increase in the elderly and that it is important to measure receptor properties on a more homogeneous leukocyte population such as PMN cells or subpopulations of MN cells as a function of aging.