Effect of IgG-coated erythrocytes and lipopolysaccharide (LPS) tolerance on the depression of vascular reactivity caused by LPS

Previous studies have shown that the injection of IgG-coated erythrocytes (EIgG) increased the mortality rate caused by bacterial lipopolysaccharide (LPS) and that animals made tolerant to LPS show a decrease in the mortality rate caused by LPS. The present study determined the effect of the injection of EIgG and of LPS tolerance on the depression of vascular reactivity caused by LPS in vivo or in vitro. For in vivo studies, LPS was injected intravenously into rats 2 h after the injection of E or EIgG. Aortae were removed 90 min after the injection of LPS, and cumulative concentration-response curves to phenylephrine were performed in helically cut aortic strips. LPS (.1 mg/kg) caused a 21% decrease in the maximum tension developed in response to phenylephrine in aortae from animals given erythrocytes. In contrast, animals given EIgG showed a 63% decrease in maximum tension following the injection of this dose of LPS. For in vitro studies, the depression of vascular reactivity caused by incubation with LPS of aortae from rats injected with EIgG was determined. As with the in vivo studies, there was a greater depression of vascular reactivity caused by incubation with LPS of aortae taken from animals injected with EIgG. Similar studies were carried out with rats made tolerant to LPS. Tolerance was induced by giving a regimen of five daily injections of LPS. Following the injection of LPS (1 mg/kg), the maximum tension of aortae from sham tolerant animals was depressed 63%, while aortae from LPS tolerant animals were depressed only 16%.