Roles of nitric oxide synthases in platelet-activating factor-induced intestinal necrosis in rats

Objective To examine the role of constitutive and inducible nitric oxide synthases (cNOS and iNOS) in platelet-activating factor (PAF)-induced shock and intestinal injury. Design Prospective, randomized, controlled experimental study. Setting Hospital research laboratory. Subjects Young adult male Sprague-Dawley rats were anesthetized and studied. Interventions Rats were injected with PAF, either alone or after the following pretreatments: a) selective iNOS inhibitors aminoguanidine or S-methylisothiourea; b) 3-morpholinosydnonimine, a NO donor; c) S-methylisothiourea + 3-morpholinosydnonimine; and d) antineutrophil antibody (to deplete neutrophils). Measurements and main results Blood pressure, hematocrit, white blood cell counts, intestinal injury, and intestinal cNOS and iNOS activities were assessed. We found that: a) cNOS is the predominant NOS in the intestine and its activity is inversely correlated to the level of tissue injury; b) there is a time-dependent increase in cNOS activity in sham-operated animals, which was abolished by PAF; c) Western blotting and immunohistochemistry showed iNOS present in the normal intestine, localizing mainly in crypt cells; d) iNOS inhibitors attenuated PAF-induced injury in animals with high cNOS activity, but had no protective effect in animals with low cNOS activity; e) 3-morpholinosydnonimine, alone or together with S-methylisothiourea, alleviated PAF-induced injury; and f) neutrophil depletion blocked the suppressive effect of PAF on cNOS and prevented injury. Conclusions We conclude that cNOS and iNOS play different roles in PAF-induced intestinal injury. Caution should be exerted concerning potential therapeutic uses of iNOS inhibitors.