Effects of pretreatment with small dose of lipopolysaccharide on cardiac function in endotoxemic rats

Objective It was reported that pretreatment with small dose of lipopolysaccharide (LPS) could protect the animal from lethal dose endotoxin. The purpose of this study was to investigate the effects of pretreatment with small dose of LPS on cardiac function in endotoxemic rats and the possible mechanism. Methods Sixty male Wistar rats weighing 200-280 g were randomly divided into 3 groups: group I normal saline(NS) ( n = 12); group Ⅱ LPS (n = 24) and group Ⅲ LPS-pretreatment ( n = 24). Group Ⅱ and group Ⅲ were further divided into 3 groups: 2 h,4 h and 6 h subgroups based the time when blood sample was taken and the animal was sacrificed. The table shows the LPS given in the 3 groups: group Ⅰ Ⅱ Ⅲ0h NS NS LPS 0.25 mg·kg-1ip 24 h NS NS LPS0.5mg·kg-1ip 96 h NS LPS 10 mg·kg-1 Ⅳ LPS 10 mg·kg-1 TV The animals were anesthetized with 3 % pentobarbital 30 mg·kg ip and intubated. Right femoral artery and vein were cannulated for MAP monitoring and fluid infusion. Cardiac catheter was placed in the left ventricle for measurement of left ventricular systolic pressure (LVSP) and±dp/dt max. Blood samples were taken 2 h,4 h and 6 h after intravenous LPS (10 mg·kg-1) for determination of plasma levels of L-lactate-dehydrogenase (LDH) and creatine kinase (CK) . The animals were sacrificed right after blood sampling and the heart was removed for determination of myocardial HSP 70 expression using immuno-histochemical staining. Results LVSP and±dp/dt max gradually decreased 1h after intravenous administration of LPS in group Ⅱ (LPS group); while in group DI (pretreatment group) the cardiac contractility was maintained and LVSP,±dp/dt max did not decrease as compared with the baseline value. Plasma LDH concentration and CK activity increased significantly 4 h and 6 h after intravenous IPS in group Ⅱ . The plasma LDH and CK levels were significantly lower in groupⅢthan those in group Ⅱ ( P 0.05). In group Ⅲmyocardial HSP 70 expression was significantly higher than that in group I and Ⅱ . ( P 0.05). Conclusion Administration of a small dose of LPS before endotoxin challenge can protect heart from injury induced by endotoxin in rats. The mechanism may involve the induction of HSP Ⅱ70 protein expression in heart.