ELECTRON-PARAMAGNETIC-RESONANCE INVESTIGATIONS OF NITROSYL COMPLEX-FORMATION DURING ENDOTOXIN TOLERANCE

The prior administration of low dose endotoxin induces a state of hypo responsiveness or tolerance to the lethal effects of endotoxin. It is generally accepted that macrophages are main cellular components in th e development of tolerance, hence, nitric oxide ((NO)-N-.) as one of t he macrophage mediators may play a role in host defense mechanisms dur ing tolerance. In this study, we utilized EPR spectroscopy to directly detect nitrosyl complexes as products of (NO)-N-. in whole blood, liv ers and intestines of lipopolysaccharide (LPS)-tolerant rats. Male Spr ague-Dawley rats were injected with a ''low dose'' LPS (0.5 mg/kg) 12- 168 h prior to a ''high dose'' LPS (3 mg/kg), then sacrificed 6 h late r. EPR signals of nitrosyl hemoprotein complexes were detected in spec imens after high dose LPS. The post-LPS EPR signals-of nitrosyl comple xes from all samples were attenuated by a prior injection of low dose LPS. The signals of dinitrosyl-iron-dithiolate became apparent in samp les from tolerant rats as signals of nitrosyl hemoprotein decreased. T he maximal tolerance in terms of diminished (NO)-N-. production was ob served when low dose LPS was given 48-96 h prior to high dose LPS. Hem oglobin concentrations in the intestine used as biomarkers of hemorrha gic damage, were concomitantly attenuated in the jejunum of tolerant r ats. These results together with our previous studies indicate that su ppression of (NO)-N-. production may contribute to the amelioration of hepatic and intestinal injury during endotoxin tolerance.