The effects of theophylline on beta 2-adrenoceptors on polymorphonuclear leukocytes of asthmatic children and juveniles. Increase in receptor density and prevention of agonist-induced down-regulation.

The density (Bmax) and affinity (KD) of beta 2-adrenoceptors in polymorphonuclear leukocytes (PMN) were measured in 29 children and juveniles with mild or moderate asthma and in 25 healthy control subjects using the highly specific radioligand (+/-)-125I-cyanopindolol. No significant difference in Bmax was found between asthmatic subjects without medication and the control group. The asthmatic subjects were divided into four different groups by their actual medication: no medication, adrenergics, theophylline, adrenergics plus theophylline. Analysis of variance revealed highly significant differences between these groups for Bmax (P = 0.0016) but not for KD. In asthmatics on adrenergic therapy Bmax was significantly lower (995 +/- 415) than in asthmatics without medication (1660 +/- 521; P = 0.008). In contrast, Bmax in asthmatics on theophylline therapy was significantly higher (2137 +/- 231; P = 0.009) than in the controls. Bmax was average in the group of asthmatics treated with both adrenergics and theophylline (1619 +/- 547). It is concluded that in asthmatic subjects therapy with theophylline increases the density of beta 2-adrenoceptors and partly prevents their down-regulation induced by adrenergic therapy.