1. Responsiveness of the β-adrenoceptor adenylate cyclase system was measured in lymphocytes from healthy young and old subjects by incubating the cells with isoprenaline in the presence of a phosphodiesterase inhibitor and by measuring production of adenosine 3′:5′-cyclic monophosphate (cyclic AMP) with a competitive binding assay.

2. The two groups did not differ significantly in the levels of cyclic AMP produced or in the concentration of isoprenaline required to give half-maximal stimulation of the cells (ED50).

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