The purpose of this study was to elucidate likely signal transduction pathways in activated bovine neutrophils, by comparing the effects of various inhibitors on the bovine neutrophil respiratory burst and degranulation in vitro. The protein kinase C(PKC) inhibitors staurosporine, and chelerythine, and the beta-adrenergic receptor antagonist DL-propranolol, markedly inhibited opsonized zymosan (OZ) stimulated luminol-dependent chemiluminescence (LDCL). The G-protein inhibitor pertussis toxin (PT), the protein tyrosine inhibitor genistein, and the calcium channel blocker verapamil also reduced LDCL in a dose-dependent manner. In contrast, the lipoxygenase inhibitor zileuton had only a slight effect, and the cyclooxygenase inhibitor indomethacin had no effect on LDCL. The effects of these inhibitors on degranulation was also examined. Staurosporine, propranolol, and pertussis toxin significantly decreased primary granule (beta-glucosaminidase) release in response to OZ. These inhibitors also significantly reduced both phorbol myristate acetate (PMA)-induced primary and secondary granule (lactoferrin) release. Regulation of secondary granule (lactoferrin) release was complex, as it was significantly depressed by propranolol, enhanced by PT and unaffected by staurosporine. These findings suggest that PKC, beta-adrenergic receptors, G-proteins, protein tyrosine kinase(s) and Ca(2+) uptake, may all be involved in some part of the process of bovine neutrophil activation. Moreover, stimulation of LDCL and degranulation may be mediated through distinct signal transduction pathways.