Potent bronchodilating effects of enprofylline and theophylline on contractions induced by egg albumin or by slow reacting substance (SRS).

Isolated sensitized guinea pig tracheal smooth muscle tone was induced by use of egg albumin or SRS-A (slow reacting substance of anaphylaxis). The dose-response relationships of theophylline and enprofylline were studied on these preparations. Enprofylline was more potent than theophylline in relaxing the egg albumin- or SRS-A-induced tracheal muscle tone. The theophylline relaxation-curve was significantly shifted to the left after addition of adenosine-deaminase to the egg albumin-contracted trachea, but this was not observed with the enprofylline relaxation-curve. In SRS-A-contracted tracheas, the addition of adenosine-deaminase did not significantly alter the relaxation curves of theophylline or enprofylline. It is therefore suggested that the relaxing effects of theophylline and enprofylline on SRS-A-induced contractions, at the therapeutically relevant concentrations demonstrated in this study, might be of importance for the anti-asthmatic effects of xanthines.