Rapid cooling after acute hyperthermia alters intestinal tissue morphology and increases the systemic inflammatory response in pigs

The study objective was to determine the direct effects of rapid cooling after acute hyperthermia on intestinal morphology and inflammatory response in pigs. In 4 repetitions, male pigs (N=36; 88.7±1.6 kg) were exposed to thermoneutrality (TN; n = 3/rep; 19.5±0.1°C) for 6 h, or heat stress (HS; 36.4±0.1°C) for 3h, followed by a 3h recovery period of rapid cooling (HSRC; n=3/rep; rapid TN exposure and ice water dousing for 1.5h) or gradual cooling (HSGC; n=3/rep; gradual decrease from HS to TN). Rectal (T_R) and gastrointestinal-tract temperatures (T_GI) were obtained every 15 min for 6h. In repetitions 1 and 2, blood was collected at 60 and 180 min during HS, and 30 and 60 min during recovery, and then pigs were euthanized at 180 min of recovery and duodenum, ileum, and colon tissue were collected to evaluate intestinal morphology. HS increased (p<0.01) maximum T_R (40.7°C) and T_GI (41.5°C) compared to TN treatment (38.9 and 39.3°C, respectively). Recovery reduced T_R (p<0.01; 0.4°C) in HSRC versus HSGC pigs, but T_GI was similar (40.7°C). HSRC reduced (p<0.01) villus height to crypt depth ratio in the duodenum (34%) and ileum (46%) versus HSGC pigs. Serum [LPS] was greater in HSRC pigs (p=0.04; 68.5 and 52.4%, respectively) compared to TN and HSGC pigs, and [TNFα] tended to be greater (p=0.06; 41.2%) compared to HSGC pigs during recovery. In summary, rapid cooling reduced T_R but had no effect on T_GI and this may be linked to increased intestinal damage and a systemic inflammatory response.

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