Résumé : Since endotoxin-induced vascular hyporeactivity to phenylephrine is enhanced in Mg-deficient rats, this study was designed to determine whether endotoxin directly enhances nitric oxide (NO) production in thoracic aortas isolated from Mg-deficient rats in vitro. Thoracic aortas isolated from Mg-deficient and control rats were cultured for 6 h with or without endotoxin (LPS). LPS (0.01-1.0 μg) increased NO production in a concentration-dependent manner. NO production in the presence of 0.1 and 1.0 μg/mL LPS was significantly higher in Mg-deficient rat aortas compared to aortas from control rats. The enhanced NO production was not significantly affected by endothelium-denudation. LPS-stimulated NO production was fully inhibited by a selective iNOS inhibitor, 1400W (0.1, 1.0 μM), in control rat aortas, but in Mg-deficient rat aortas inhibition by 1400W was only partial. A similar inhibitory effect was observed with anti-CD14 and anti-TLR4 antibodies. These results suggest that endotoxin enhances NO production in Mg-deficient rat aortas directly, and that endotoxin receptors might, at least in part, contribute to this enhancement.