Chronic leukotriene inhibition in the rat fails to modify the toxicological effects of a cyclooxygenase inhibitor.

A 5-week study was carried out in rats using a leukotriene biosynthesis inhibitor (MK-886; 3-[1-(4-chlorobenzyl)-3-t-butylthio-5-isopropylindol-2-yl]-2,2- dimethylpropanoic acid) at a dose of 300 mg.kg-1 x day-1, this being sufficient to produce > 90% inhibition of ex vivo leukotriene B4 synthesis in rat blood, and a cyclooxygenase inhibitor (indomethacin, 4 and 6 mg.kg-1 x day-1) to ascertain whether inhibition of leukotriene biosynthesis would potentiate or inhibit the toxicity associated with the administration of nonsteroidal anti-inflammatory drugs (NSAIDs), in particular the gastrointestinal damage. Treatment with indomethacin alone or in combination with MK-886 resulted in the toxicity normally associated with NSAIDs, including gastrointestinal lesions. No toxicity was associated with the administration of MK-886 alone, and MK-886 had no significant effect on the incidence of gastrointestinal lesions produced by indomethacin. These results indicate that leukotrienes are not significant mediators of NSAID-induced gastroenteropathy in the rat.