Beta Adrenergic Receptors of Polymorphonuclear Particulates in Bronchial Asthma

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Abstract
We have tested the beta adrenergic receptor theory of bronchial asthma by determining the number and affinity of binding sites of the beta adrenergic radioligand [3H]dihydroalprenolol (DHA) and the activity of adenylate cyclase in broken cell preparations of polymorphonuclear leukocytes (PMN). We studied 31 control subjects (group 1), 30 asthmatics receiving no systemic adrenergic medication (group 2), and 17 asthmatics receiving adrenergic agonists systemically (group 3). Control subjects and asthmatics taking no adrenergic drugs bound similar amounts of DHA at 0.5 nM and 30 nM DHA and had about 900 binding sites per PMN. In contrast, asthmatics receiving adrenergic agonists had a >70% decrease in their number of DHA binding sites per PMN (254±57). In a subset of our three groups of subjects (eight from group 1, six from group 2, and five from group 3) we measured DHA binding at several DHA concentrations and found similar values (0.4-0.7 nM) for the dissociation constant of DHA among these subjects. In further studies we examined the interaction of the agonist (−)-isoproterenol with beta adrenergic receptors in 8 normal subjects and 10 asthmatics not receiving adrenergic medication. We tested the ability of isoproterenol to compete for DHA binding sites and to stimulate adenylate cyclase in sonicates prepared from PMN and examined under identical conditions. The dissociation constants for the competition of isoproterenol for DHA binding sites in normal and asthmatic subjects were virtually identical (∼1.0 μM). In addition, the (activation constant) values for stimulation of adenylate cyclase were similar (0.16-0.19 μM) in the two groups of subjects. Thus, these data suggest that asthma per se is not associated with alteration in either the number or affinity of beta adrenergic receptors in PMN. Our findings indicate that previous reports of abnormal beta adrenergic receptor function in asthmatic patients may in part be explained by prior treatment of such patients with adrenergic agonists. Because the asthmatics who received adrenergic agonists in our study tended to be more ill and to receive additional medication compared to subjects in group 2, we cannot rule out unequivocally that severe asthma may be associated with decreased binding to beta adrenergic receptors. Nevertheless, we conclude that beta adrenergic receptors on PMN from asthmatics are relatively normal unless such patients are treated with adrenergic agonists.