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Altered β-Adrenoceptor Internalization Does Not Explain Reduced β-Adrenergic Responsiveness in the Elderly^*

D. J. SILBERSTEIN, J. RIGBY, J. MERRELL, T. NASLUND and A. J. J. WOOD

Department of Clinical Pharmacology, Vanderbilt University, School of Medicine Nashville, Tennessee 37232

To determine whether altered β-adrenoceptor internalization contributes tothe reduced adrenergic responsiveness of the elderly, the ability to internalize β-adrenoceptors in young and elderly men was studied by in vitro exposure of whole lymphocytes to a range of isoproterenol concentrations. The total numbers of receptors per cell were similar inthe two groups [young, 1645 ± 206 ± SE); elderly, 1707 ± 120], as were the basal levels of β-adrenoceptor internalization (young, 8.85 ±1.09%; elderly, 8.73 ± 1.35%). Incubation in the presence of isoproterenol resulted in dose-dependent internalization of receptors. The EC₅₀ values for isoproterenol-induced internalization were similar in the young (20.7 ± 3.5 nmol/L) andelderly groups (26.9 ± 4.4 nmol/L). These results suggest that altered receptor internalization does not contribute to impaired β-adrenoceptor function in the elderly.

^* This work was supported by USPHS Grants HL-14192, AG-01395,and RR-95.

To whom requests for reprints should be addressed.

Received May 18, 1988.

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