β2-adrenoceptor up-regulation in relation to cAMP production in human lymphocytes after physical exercise

The effect of isotonic bicycle exercise on β 2 -adrenoceptors and cAMP production in lymphocytes was studied. The origin of the newly exposed receptors was studied by measuring radioligand binding in the presence of hydrophylic or lipophylic `cold' ligands. During exercise β 2 -adrenoceptor density increased from 1207 ± 144 to 1776 ± 152 sites/cell (56 ± 14%). Isoprenaline induced an increase in cAMP synthesis, which was 68 ± 15% higher than those values measured before the test. Forskolin did not induce a higher increase in cAMP production after exercise. The increase in receptor density seems not to be due to a transfer of internalized receptors to the membrane surface. We conclude that physical exercise induces an up-regulation of β 2 -adrenoceptors on lymphocytes and that these adrenoceptors are functional.