Leukocytic epinephrine receptors of normal and asthmatic individuals

Abstract

To determine if the hypothesized beta adrenergic blockade in asthma is located at the level of the hormone receptor, we have compared the number and binding affinity of leukocytic epinephrine receptors in normal and asthmatic subjects. Human leukocytes, but not human erythrocytes, possess low-affinity epinephrine receptors. When saturated, each leukocyte binds approximately 1.0 times 10-6 molecules of epinephrine. Binding of 3H DL-epinephrine was largely inhibited by excess unlabeled L-epinephrine. The binding was reversible and involved both the D and L forms of 3H DL-epinephrine. Inhibition studies with nonradioactive isoproterenol, norepinephrine, propranolol, and tolazoline produced results consistent with the interpretation that the leukocytes contained both alpha and beta adrenergic receptors. Two procedures, subcellular fractionation of lymphocytes and incubation of leukocytes in 0.1 per cent trypsin, permitted the demonstration that most of the catecholamine binding occurred at the plasma membrane. Thin-layer chromatography of the bound 3H DL-epinephrine after its extraction from the leukocytes permitted the interpretation that the hormone had fully retained its chemical structure. In addition, epinephrine binding was associated with cAMP production. Leukocytic epinephrine receptors of 10 asthmatic and 9 normal individuals were compared and found not to be substantially different in number or binding affinity.