We studied the relationship between mode of activation of isolated human eosinophils and in situ responsiveness in isolated tracheal smooth muscle (TSM) of guinea pigs. Human peripheral blood eosinophils were activated with either 10(-7) M phorbol myristate acetate (PMA) or 10(-6) M formyl-methionyl-leucyl-phenylalanine (fMLP) + 5 micrograms/ml cytochalasin 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 content) and PMA (10.0 +/- 2.8% of total content; P = NS). Topical application 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 preparations (P < 0.03 vs. baseline); cells activated with PMA caused no contractile 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 acetylcholine 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 cells (P < 0.01). Both AT and augmented muscarinic responsiveness were blocked by pretreating the eosinophils with 200 microM A-63162, an inhibitor of 5-lipoxygenase, before activation with fMLP+CYB. We demonstrate that eosinophils activated comparably (as assessed by EPO secretion) cause augmented muscarinic responsiveness and/or direct contraction of guinea pig TSM through secretion of a product of the 5-lipoxygenase pathway.(ABSTRACT TRUNCATED AT 250 WORDS)