Physical activity decreases the number of β-adrenergic receptors on human lymphocytes

On intact human lymphocytes a specific binding site (BS) for125I-Cyanopindolol (125I-CYP), a derivative of the β-blocking drug pindolol, was characterized. Inhibition of binding for catecholamines in the following order of potency: l-isoprenaline > l-adrenaline > l-noradrenaline proves the BS as a β2-receptor subtype. In 77 healthy persons (36 females, 41 males) the number of BS amounted to 2,639±125 BS/cell without any significant correlation to age (17–86 years) or sex. The dissociation constant (KD) indicating the affinity of iodocyanopindolol to the BS on intact lymphocytes was K d =1.9±1.1×10−10 M. A change of the number of β-adrenergic receptors on intact human lymphocytes has been measured previously in asthmatics and in the myocardium of patients with congestive heart failure. We investigated a possible change in the β-receptors on lymphocytes by physical and mental activity (“stress”) in physicians going about their daily routine work. Persons left alone in a hospital room reading or sleeping were defined as “inactive controls”. The number of BS on intact lymphocytes was significantly higher in inactive persons at 8 a.m. (2,230±482 BS) compared to active persons (1,743±285 BS;P<0.05) and at 1 p.m. (2,394±253 BS vs 1,733±556;P<0.05) but not different at 6 p.m. (1,634±578 BS vs 1,768±588 BS;P<0.1). The K d remained unchanged under all conditions. The serum noradrenaline and adrenaline levels were also measured during the day. The serum adrenaline levels were higher in the active group than in the inactive group at 8 a.m. (46±11 pg/ml vs 22±8 pg/ml;P<0.01) and at 1 p.m. (36±13 pg/ml vs 13±5 pg/ml;P<0.01) but not at 6 p.m. (37±28 pg/ml vs 13±6 pg/ml;P<0.1). Our data clearly show higher serum adrenaline levels but fewer BS on intact human lymphocytes in active persons than in inactive persons at 8 a.m. and 1 p.m. The high catecholamine serum levels may cause a down-regulation of the number of β-receptors in the active persons.