The magnitude of physical exercise-induced hyperthermia is associated with changes in the intestinal permeability and expression of tight junction genes in rats

We investigated whether the magnitude of exercise-induced hyperthermia influences intestinal permeability and tight junction gene expression. Twenty-nine male Wistar rats were divided into four groups: rest at 24 degrees C and exercise at 13 degrees C, 24 degrees C or 31 degrees C. The exercise consisted of a 90-min treadmill run at 15 m/min, and different ambient temperatures were used to produce distinct levels of exercise-induced hyperthermia. Before the experimental trials, the rats were treated by gavage with diethylenetriaminepentaacetic acid labeled with technetium-99 metastable as a radioactive probe. The rats' core body temperature (T-CORE) was measured by telemetry. Immediately after the trials, the rats were euthanized, and the intestinal permeability was assessed by measuring the radioactivity of blood samples. The mRNA levels of occludin and zonula occludens-1 (ZO-1) genes were determined in duodenum samples. Exercise at 24 degrees C increased T-CORE to values close to 39 degrees C, without changing permeability compared with the resting trial at the same environment. Meanwhile, rats' T-CORE exceeded 40 degrees C during exercise at 31 degrees C, leading to greater permeability relative to those observed after exercise in the other ambient temperatures (e.g., 0.0037%/g at 31 degrees C vs. 0.0005%/g at 13 degrees C; data expressed as medians; p < 0.05). Likewise, the rats exercised at 31 degrees C exhibited higher mRNA levels of ZO-1 and occludin genes than the rats exercised at 24 degrees C or 13 degrees C. The changes in permeability and gene expression were positively and significantly associated with the magnitude of hyperthermia. We conclude that marked hyperthermia caused by exercise in the warmer environment increases intestinal permeability and mRNA levels of tight junction genes.