Density and functioning of human lymphocytic β‐adrenergic receptors during prolonged physical exercise

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Abstract
In order to study the regulation of β‐adrenergic receptor number and function in response to prolonged physical effort, lymphocytic β‐adrenoceptor density (determined by (‐)[125I]iodocyanopindolol binding), lymphocytic basal and isoproterenol‐stimulated cyclic AMP (cAMP) production and concentrations of plasma catecholamines were measured before and during 3 h running exercise in eight healthy volunteers. A significant (P < 0.01) increase of the lymphocytic β‐adrenoceptor density from 45±4 to 81 ± 9 fmol mg‐1protein (mean ± SEM) took place during the first hour of exercise. As the exercise was continued for up to 2.1–3 h, the receptor densities did not change significantly any more and remained elevated (72 ± 9 fmol mg‐1protein) in comparison to the resting levels (P < 0.02). The isoproterenol‐stimulated cAMP production of the lymphocytes increased during the first hour of running from 190 ± 36 to 269 ± 56 pmol mg‐1protein (P < 0.01) and returned to the resting level at the end of the exercise (182 ± 38 pmol mg‐1protein). The mean levels of plasma catecholamines increased ˜ sixfold during the first hour of exercise and remained elevated until the end of the running. This study demonstrates that the β‐adrenergic receptor system is activated in lymphocytes during prolonged aerobic physical exercise. This activated state becomes, however, attenuated within 2–3 h of exercise as indicated by a diminishing ability of β‐adrenoceptors to mediate catecholamine‐induced cAMP production.

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