Protective effects of heat stress from endotoxin induced lung injury and shock is attributed to the induction of a heat stress protein (HSP70).In-vitro, endotoxin prior to heat has been shown to increase TNF production and decrease HSP70 induction. The objective of this study was to determine if endotoxin decreases the synthesis of heat induced HSP70in-vivo. Twenty five rats were randomly assigned to 5 groups: Group 1, controls, received saline infusion. Group 2 received only endotoxin (LPS) infusion over 2 min. Group 3 received heat stress (42°C for 10 min). Group 4 received heat stress followed two hrs later by LPS infusion. Group 5 received LPS infusion followed two hrs later by heat stress. Animals were sacrificed two hrs after final treatment, the spleen was removed, splenocytes were washed, and inducible HSP70 was determined by Western blot. Densitometry analysis for each HSP band was compared to its corresponding actin band and reported as% actin. Group 1, control spleen cells were negligible for inducible HSP70 (0.58 ±0.63). Group 2, treated with LPS only were similar to controls (0.33 ±0.44). Group 3, receiving heat stress only had the greatest amount of HSP70 induced (84.4 ±20.2) and were similar to group 4, treated with heat stress followed by LPS (65.4 ±10.2). However, HSP70 induction was suppressed in group 5, pretreated with LPS prior to heat stress (21.0 ±8.0) which was different from groups 3(p<0.007) and group 4 (p<0.004). The suppression of HSP 70 in group 5 was reversed by washing the splenocytes and incubating them for two additional hours which resulted in increased HSP70 synthesis (70.8 ±33.9) similar to group 3.

Conclusion: Endotoxemia suppresses heat-induced HSP 70 synthesis in rat splenocytes. The mechanism of this apparently reversible suppression of HSP70 synthesis by endotoxin needs to be explored.