Cardiac sensitivity to isoprenaline, lymphocyte β-adrenoceptors and age

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Abstract
The heart rate response to isoprenaline in 11 subjects aged 19-46 yr was compared with lymphocyte .beta.-adrenoceptor numbers and lymphocyte cAMP responsiveness. The dose of isoprenaline required to increase heart rate by 25 beats/min (CD25) increased as a function of age (r 0.79; P < 0.01). Lymphocyte receptor numbers also correlated directly with age (r 0.61; P < 0.05), but there was no true correlation between CD25 and lymphocyte receptor numbers. Baseline and maximum lymphocyte cAMP concentrations in response to isoprenaline stimulation in vitro were unrelated to age, CD25 or receptor numbers. A reduced responsiveness with age and a rise in receptor numbers in young and middle-aged adults are indicated. The decline in the heart response to isoprenaline was unrelated to any measurable change in .beta.-adrenoceptor concentration or responses, at least in the isolated lymphocyte.