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 c 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.