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The main beta-blockers are propranolol, acebutolol, alprenolol, atenolol, carvedilol, esmiolol, etc. They block the action of endogenous catecholamines (adrenaline and noradrenaline). Almost, all immune cells have beta-adrenoreceptors, that are used by catecholamines to regulate their functions. Catecholamines are key hormones in the modulation of the immune response, so the inhibition of their receptors will affect the immune response and the cells involved on it. For example, decreased chemotaxis and phagocytosis capacity following acute exercise when neutrophils' beta-adrenoreceptors are blocked has been observed, since noradrenaline can not exert it. Therefore, athletes who take beta-blockers would be more susceptible to infections since their phagocytic cells would not be impeded. Noradrenaline also stimulates chemotaxis, phagocytic and microbicide capacity of macrophages, but it also needs beta-receptors.
A common dogma of the 1980s and early 1990s was that norepinephrine stimulation suppressed lymphocyte function. Both, norepinephrine and Isoproterenol increased the number of lymphocytes leaving the spleen, without any apparent alterations in blood flow. Alterations in lymphocyte adhesion molecule expression may mediate the norepinephrine-induced increase in the number of circulating lymphocytes. Therefore, the intake of beta-blockers can also alter the flux of immune cells and their immunosurveillance especially during exercise. For example, exercise-induced increases in leukocyte numbers enhance following propranolol treatment. Propranolol treatment interferes with the adrenergic regulation of circulating leukocyte numbers by blunting psychological stress effects but enhancing exercise effects.
Noradrenaline and adrenaline at high concentrations stimulate T lymphocytes production, but this stimulation is inhibited by beta-blockers like propranolol; but on the contrary high concentrations of noradrenaline inhibit the proliferation of lymphocytes which regulate the proliferative response. The intake of beta-blockers by healthy people can alter immune equilibrium above all during stress situations as exercise.
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