Dilation of the distal convoluted tubule induced by repeated heat exposure in rats model

Thermal therapy (TT) has developed as a nonpharmacological strategy for various diseases, but little is known about its impact on the kidneys. This study conducted an animal experiment to elucidate this impact. We randomized 12 rats to control and TT groups and subjected them to 24 °C and 41 °C, respectively, once a day for four weeks. We monitored blood component changes weekly and examined rat kidneys pathologically after the trial. Cutaneous flux and renal blood flow were assessed before and during the intervention. The cross-sectional area of the distal convoluted tubule (DCT) significantly increased in the TT group compared to the control group (P < 0.001). The TT group's DCT showed an average perimeter elongation of 75.9 %, which is explained by mechanical strain and the proliferation of epithelial cells. Significant increases at 14 days (P < 0.05) in blood urea nitrogen, creatinine, and uric acid levels indicated that renal damage was the cause of these occurrences. Furthermore, this damage is caused by thermally induced renal ischemia, as indicated by a 21.3 % decrease in mean blood flow in the renal artery, which was also evidenced by a 65.2 % increase in mean cutaneous flux and a significant rise in red blood cell count (P < 0.05). Sirius red staining showed that there was no difference in fiber expression between the two groups. Although no progression of renal fibrosis was observed, repeated heat exposure could induce the dilation of DCT. These findings may guide the redesign of TT protocols for patients and recreational users.