ISOPROTERENOL-INDUCED INHIBITION OF IMMUNOGLOBULIN E-MEDIATED RELEASE OF HISTAMINE AND ARACHIDONIC-ACID METABOLITES FROM THE HUMAN-LUNG MAST-CELL

Abstract

The inhibitory effect of isoproterenol was examined on the release of histamine, leukotriene C4 (LTC4), and prostaglandin D2 (PGD2) from human lung mast cells. Isoproterenol was more potent in inhibiting anti-immunoglobulin (Ig) E-induced LTC4 and PGD2 release than histamine release from the dispersed lung cell preparations (2-5% mast cells). The negative log molar EC50 values of isoproterenol for inhibiting histamine, LTC4 and PGD2 release were 8.2 .+-. 0.2, 8.9 .+-. 0.2 and 8.7 .+-. 0.3, respectively (mean .+-. S.E.M., n = 8). Isoproterenol seldom inhibited histamine release by more than 60%, but usually abolished the release of LTC4 and PGD2. The potency of propranolol (KB = 6 .times. 10-10 M) was the same for competitively antagonizing isoproterenol mediated inhibition of histamine, LTC4 or PGD2 release. Using the irreversible beta adrenergic receptor antagonist, bromoacetylalprenololmenthane, the estimated dissociation constant of isoproterenol was 2 .times. 10-7 M irrespective of whether inhibition of anti-IgE-induced histamine or LTC4 release was examined. When the divalent cation ionophore A23187 was used to induce histamine release, isoproterenol had either no effect or potentiated the release. In contrast, isoproterenol was capable of virtually abolishing A23187-induced LTC4 release. Qualitatively similar effects of isoproterenol were observed on purified mast cell preparations (> 80% mast cells); however, the potency of isoproterenol in inhibiting mediator release from these preparations was reduced. The results demonstrate that there is a substantial receptor reserve for isoproterenol-mediated inhibition of histamine, LTC4 and PGD2 release from the human lung mast cells. The intrinsic efficacy of isoproterenol in inhibiting anti-IgE-induced release of arachidonic acid metabolites is approximately 3 times greater than that for inhibiting histamine release. The results with the ionophore A23187 suggest that this may be explained by a direct effect of beta adrenergic receptor activation of arachidonic acid metabolism in the mast cell in addition to its potent inhibitory effect on the stimulus induced by the crosslinking of mast cell bound IgE.