EFFECT OF MODE OF ACTIVATION OF HUMAN EOSINOPHILS ON TRACHEAL SMOOTH-MUSCLE CONTRACTION IN GUINEA-PIGS

We studied the relationship between mode of activation of isolated hum an eosinophils and in situ responsiveness in isolated tracheal smooth muscle (TSM) of guinea pigs. Human peripheral blood eosinophils were a ctivated with either 10(-7) M phorbol myristate acetate (PMA) or 10(-6 ) M formyl-methionyl-leucyl-phenylalanine (fMLP) + 5 mug/ml cytochalas in B (CYB), and activation was confirmed by measurement of eosinophil peroxidase (EPO) secretion by kinetic assay. EPO secretion was similar after activation with fMLP + CYB (10.2 +/- 3.2% of total eosinophil c ontent) and PMA (10.0 +/- 2.8% of total content; P = NS). Topical appl ication of 6 X 10(6) eosinophils/cm2 activated with fMLP + CYB to the TSM segment caused 0.51 +/- 0.14 g/cm active tension (AT) in five prep arations (P < 0.03 vs. baseline); cells activated with PMA caused no c ontractile response (0.04 +/- 0.03 g/cm AT, P = NS vs. baseline). Both PMA- and fMLP + CYB-activated cells caused augmentation of muscarinic responsiveness of guinea pig trachealis. The dose of intravenous acet ylcholine required to cause a threshold response (ED0.3) was -7.3 +/- 0.1 log mol/kg at baseline vs. -8.7 +/- 0.5 log mol/kg after treatment with fMLP + CYB-activated eosinophils (P = 0.05) and -6.9 +/- 0.1 log mol/kg at baseline vs. -7.5 +/- 0.1 log mol/kg after PMA-activated ce lls (P < 0.01). Both AT and augmented muscarinic responsiveness were b locked by pretreating the eosinophils with 200 muM A-63162, an inhibit or of 5-lipoxygenase, before activation with fMLP + CYB. We demonstrat e that eosinophils activated comparably (as assessed by EPO secretion) cause augmented muscarinic responsiveness and/or direct contraction o f guinea pig TSM through secretion of a product of the 5-lipoxygenase pathway. However, TSM contraction and augmented muscarinic responsiven ess caused by activated eosinophils are not predicted by EPO secretion , a common marker of eosinophil activation in vitro.