Objective:To evaluate the intestinal function in rats with exertional heat stroke (EHS) and explore the protective role of Ruifuping pectin (RFP) against heat related intestinal mucosal injury.Methods:One hundred and twenty healthy special pathogen free (SPF) male Sprague-Dawley (SD) rats were randomly divided into normothermic control group, EHS model group, hyperthermic plus drinking water group (H 2O+EHS group) and hyperthermic plus pectin group (RFP+EHS group) with 30 rats in each group. The rats in the H 2O+EHS group and RFP+EHS group were given water 20 mL/kg or RFP 20 mL/kg orally for 5 days during adaptive training period. After 1 week, the temperature control range was adjusted to (37±1)℃ using the temperature control treadmill, and the rat model of EHS was reproduced by one-time high temperature exhaustive exercise. No rehydration intervention was given during the training adaptation period in the EHS model group. The rats in the normothermic control group were maintained to room temperature (25±2)℃ and humidity (55±5)% without other treatment. Behavior tests including withdraw response, righting, and muscle strength were performed immediately after onset of EHS. Blood of inferior vena cava was collected, and the serum inflammatory cytokines [tumor necrosis factor-α (TNF-α) and interleukins (IL-6, IL-1β, IL-10)] and activity of diamine oxidase (DAO) were detected by enzyme linked immunosorbent assay (ELISA). The intestinal mucosa was collected, after hematoxylin-eosin (HE) staining, and Chiu score was performed to assess EHS induced pathological changes under light microscope. Results:The rats in the EHS model group had behavioral, inflammatory and pathological changes, such as delayed withdraw response and righting, decreased forelimb pulling, increased inflammatory index, and obvious intestinal mucosal injury, which indicated that the reproduction of the EHS model was successful. There was no significant difference in above parameters between the H 2O+EHS group and the EHS model group except that the inflammatory index in the RFP+EHS group was improved. Compared with the EHS model group, the withdraw reflex to pain and righting after RFP pretreatment in the RFP+EHS group were significantly improved (righting score: 1.4±0.2 vs. 0.3±0.2, withdraw reflex to pain score: 1.0±0.1 vs. 0.2±0.1, both P < 0.05), the muscle strength was significantly increased (N: 13.0±0.5 vs. 8.2±0.6, P < 0.01). The levels of pro-inflammatory factors in the RFP+EHS group were significantly lower than those in the EHS model group [TNF-α (ng/L): 67.5±9.2 vs. 194.3±13.7, IL-6 (ng/L): 360.0±54.1 vs. 981.2±84.4, IL-1β (ng/L): 33.7±9.0 vs. 88.7±6.1, all P < 0.01], while the level of anti-inflammatory factor IL-10 was higher than that in the EHS model group (ng/L: 208.7±10.5 vs. 103.7±7.0, P < 0.01). The degree of intestinal mucosal injury in the RFP+EHS group was less severe than that in the EHS model group, and the Chiu score and DAO were significantly lower than those in the EHS model group [Chiu score: 1.5±0.2 vs. 3.8±0.0, DAO (U/L): 83.7±6.7 vs. 128.7±10.5, both P < 0.05]. Conclusions:High temperature training can damage the intestinal barrier function, and induce endotoxemia and systemic inflammatory response syndrome (SIRS) in rats. Oral prophylactic RFP can protect the intestinal barrier function, alleviate SIRS, and promote the recovery of basic nerve reflex and muscle strength after the occurrence of EHS in rats.