ALTERATIONS OF β-ADRENOCEPTORS ON HUMAN LEUKOCYTE SUBSETS INDUCED BY DYNAMIC EXERCISE: EFFECT OF PREDNISONE

SUMMARY 1. In order to investigate exercise‐induced changes of β2‐adrenoceptors on human leukocyte subsets, β‐adrenoceptor density was determined as specific binding of [125I]‐iodocyanopindolol to granulocytes, monocytes, B and T lymphocytes of six subjects immediately before and after exercise and after 30 min of rest. 2. A 10 min graded bicycle exercise with a workload of 50–250 W caused a transient increase of granulocytes, monocytes, B and T cells of about 32, 43, 120 and 25%, respectively. 3. While the number of β2‐adrenoceptors in granulocytes remained unchanged, β‐adrenoceptor densities in B cells, T cells and monocytes increased from pre‐exercise mean values of 2730, 870 and 2400 binding sites/cell to 3500, 1230 and 3220 binding sites/cell, respectively, under physical stress. The rise in receptor numbers was accompanied by an enhanced isoprenaline‐stimulated cyclic AMP formation in unfractionated mononuclear leukocytes (MNL) of about 26% as well as by a 2–3‐fold increase in plasma catecholamine levels. Cell concentrations, β2‐adrenoceptor numbers and adrenergic responsiveness returned to normal after 30 min rest. 4. Administration of 60 mg prednisone 2 h before exercise resulted in granulocytosis and lymphopenia with a preponderant effect on the exercise‐induced rise in B cells and monocytes. Corticosteroids showed no effect on stress‐induced changes of β2‐adrenoceptors and responsiveness. 5. It is concluded that exercise‐induced increases in β2‐adrenoceptor density and adrenergic responsiveness of unfractionated MNL are caused by a release of receptor‐enriched cells into the circulation, particularly of B lymphocytes and monocytes which carry the highest β2‐adrenoceptor density.