Metabolites of arachidonic acid like prostaglandins have an established role in the pathogenesis of gallstone formation and cholecystitis, but any contribution by leukotrienes is less clear. Leukotrienes might contribute to the disease process by contracting the inflamed and (or) obstructed gallbladder, resulting in further inflammatory damage and biliary pain. To better define the role of leukotrienes, we assessed their effects on gallbladder contractility in vitro. Both leukotriene C4 (LTC4) and D4 (LTD4) had a concentration-dependent excitatory effect on guinea-pig gallbladder smooth muscle. The LTD4-receptor antagonist MK-571 (1 microM) competitively depressed the contractile response, to both LTD4 and LTC4. The source of calcium was defined using ryanodine to deplete intracellular calcium stores and nifedinine to block extracellular entry. Ryanodine (10 microM) antagonized gallbladder contraction at low concentrations of LTD4 (10(-10) and 10(-9) M). Nifedipine (1 microM) had a greater inhibitory effect on the contractile response at high concentrations of LTD4 (10(-8)-10(-6) M). LTD4-induced contractions were unaffected in tissues pretreated with the neural blocker tetrodotoxin or the muscarinic antagonist atropine. Thus, leukotrienes act directly on the gallbladder smooth muscle, causing contraction at concentrations found in models of cholecystitis, suggesting that these inflammatory mediators contribute to the symptoms and morbidity associated with gallbladder disease.