Neutrophil-derived oxidants such as hydrogen peroxide (H2O2), hypochlorous acid (HOCl), and monochloramine (NH2Cl) may contribute to gallbladder inflammation in cholecystitis. We examined the influence of oxidants on the biological activity of different agonists and antagonists of gallbladder smooth muscle function. The concentration-response curves for cholecystokinin-octapeptide (CCK-OP) and carbachol were examined before and after incubation of the tissues with NH2Cl (30 microM). The 50% effective concentration of CCK-OP was shifted from 0.5 +/- 0.09 nM (control) to 4 +/- 1.2 nM in the presence of NH2Cl. The effect of carbachol was not affected by NH2Cl. The contractile effect of CCK-OP (3 nM) was abolished by prior exposure to HOCl or NH2Cl. These actions were prevented by 60 microM glutathione. Oxidant-induced degradation of CCK-OP was confirmed by high-performance liquid chromatography and thin-layer chromatography. NH2Cl also significantly reduced the contractile response to neurokinin A, bradykinin, leukotriene D4, and phorbol 12,13-dibutyrate and the relaxant response to isoproterenol. Prior exposure of acetylcholine, histamine, serotonin, prostaglandin E2, vasoactive intestinal polypeptide, or calcitonin gene-related peptide to NH2Cl had no effect on their activity. The results indicate that NH2Cl generated during inflammation may decrease the biological activities of different agonists and antagonists of smooth muscle function.