Inhibition by isoproterenol of ovalbumin-induced contraction of tracheal strips and release of histamine from lung isolated from the actively sensitized guinea-pig

Abstract

Tracheal strips and lung parenchyma were obtained from guinea pigs actively sensitized with egg albumin (ovalbumin). Dose-response curves to ovalbumin for producing tracheal contraction and histamine release from chopped lung were shifted to the right and the maximum response reduced by isoprotenol. Small concentrations of isoproterenol exerted a selective inhibitory effect on ovalbumin-induced tracheal contractions and 100-fold larger concentrations were required to inhibit ovalbumin-induced histamine release. Practocol, a cardioselective beta adrenergic receptor antagonist, bloked the inhibitory effect of isoproterenol on histamine release at a concentration which did not alter the effect of isoproterenol on antigen-induced tracheal contraction. The dose-response curve for ovalbumin in producing tracheal contraction was approx. 2 log units to the left of that in producing histamine release. This difference cannot be explained by the presence of a receptor reserve for histamine. These results suggest that the beta adrenergic receptors mediating inhibition of antigen-induced histamine release and tracheal contraction have some different pharmacological properties. Also, histamine does not appear to be the principal mediator of the anaphylactic tracheal contraction.