Beta 2-adrenoceptor selectivity in four series of beta-adrenoceptor agonists

Current issues with beta2-adrenoceptor agonists: historical background

The discovery that dessicated adrenal glands had beneficial effects in asthma arose in 1900 following a vogue for studying organotherapy at the end of the 19th century. The adrenal hormone adrenaline was found to have sympathomimetic properties and was isolated and synthesized in 1901. The first nonselective beta-agonist, isoproterenol, was isolated in 1940, followed by the development of selective beta2-agonists in the 1960s and the introduction of the long-acting beta2-agonists in the 1990s. The introduction of beta2-selectivity reduced adverse effects, as did developments in inhaler technology that allowed subjects to inhale much smaller doses of drug selectively to the airways. The beta2-agonists are some of the more important drugs to have been developed in the 20th century. Excessive doses can cause problems, and attempts to maximize the benefit from beta2-agonists and to reduce adverse effects has led to considerable epidemiological, clinical, and mechanistic research over the last 50 yr.

An analysis of the beta 2-adrenoceptor selectivity in three series of beta-adrenoceptor agonists

The aim of the study was to analyse the beta 2-adrenoceptor selectivity earlier found in two series of catecholamines and one series of resorcinolamines (Johansson et al. 1986). The affinity of the compounds was assessed in binding studies in preparations from the guinea-pig left heart ventricle (beta 1-adrenoceptors) and the soleus muscle (beta 2-adrenoceptors) using 3H-CGP-12177 as radioligand. Further, the activation of the adenylate cyclase by the compounds was studied in the same preparations. Selectivity quotients were obtained from both functional effects and from affinity and adenylate cyclase activating studies. There was a good correlation between the selectivity quotients obtained in these two ways. Tertiary butyl substitution on the amino nitrogen gave the highest beta 2-adrenoceptor selectivity in both the catechol and resorcinol series. In comparison with their isopropyl substituted analogues the beta 2-adrenoceptor selectivity of these compounds (KWD 2026 and terbutaline) was mainly due to a change in affinity for the beta 1- and beta 2-adrenoceptors and, to a lesser degree, a change in intrinsic efficacy.

Involvement of the spleen in the endotoxin-induced deterioration of the respiratory airway and lymphocyte beta-adrenergic systems of the guinea pig

The beta-adrenergic binding sites on splenic lymphocyte membranes of the guinea pig were characterized with the radio-ligand [125I]cyanopindolol and showed a maximal number of binding sites (Bmax) of 125 fmol/mg protein and an affinity (Kd) of 170 pM. The potency of various beta-adrenoceptor antagonists to compete for [125I]cyanopindolol binding suggested that the receptor is of the beta 2 subtype. Endotoxin (1 mg/kg) induced a 35% decrease in the number of beta-adrenergic binding sites on lymphocytes, 4 days after i.p. administration. The reduction in the number of beta-adrenoceptors on the lymphocytes was accompanied by a 30% decrease in the relaxation of isolated guinea pig tracheal spirals to isoprenaline and a 20% reduction in the number of beta-adrenergic binding sites in peripheral lung tissue. The endotoxin-induced deterioration of the beta-adrenergic system in the respiratory airways was completely prevented by splenectomy. It is concluded that the spleen, and or cells or products derived from the spleen, are involved in the changes of the beta-adrenergic system in the respiratory airways and lymphocytes.