Hypoxic tubulointerstitial fibrosis and swimming exercise change expression of urotensin II and its receptor GPR14 in rats

AIM: To observe the expression of urotensin II (UII) and its receptor GPR14 in rats with hypoxic tubulointerstitial fibrosis, and to explore the changes after swimming exercise. METHODS: The animal model of hypoxic renal interstitial fibrosis was established by exposing the rats to isobaric hypoxic chamber for 7 weeks (8 h/d, 7 d/week). Forty-five male SD rats were randomly divided into normal control group (control), hypoxic 7-week group (hypoxia) and hypoxic 3-week and swimming without loads 4-week group (swimming). Serum creatinine (Scr) and blood urea nitrogen (BUN) were measured by chemical colorimetry, and UII was detected by ELISA. The content of hydroxyproline (Hyp) in the renal homogenate was assayed. The mRNA expression of UII and GPR14 were detected by RT-PCR. The protein level of UII was determined by the method of immunohistochemistry. Meanwhile, the renal specimens were prepared to observe renal interstitial fibrosis by van Gieson(VG) staining. RESULTS: The content of Scr and BUN in hypoxia group was lower than that in control group by 18.5% and 14.1%,respectively, while there was no significant difference between swimming group and hypoxia group. The content of Hyp in hypoxia group was 42.9% higher than that in control group, while swimming group was 26.1% lower than that in hypoxia group. The plasma content of UII in hypoxia group was 380.8% higher than that in control group, while swimming group was 42.6% lower than that in hypoxia group. The mRNA expression of UII in the kidneys was obviously up-regulated by 104.5% in hypoxia group compared with control group, while it was markedly down-regulated by 33.2% in swimming group compared with hypoxia group. The mRNA expression of GPR14 in the kidneys was significantly up-regulated by 35.4% in hypoxia group compared with control group. However, no significant difference between hypoxia group and swimming group was observed. The UII protein level in the kidneys of hypoxia rats was distinctly higher than that in control group and lower in swimming group than that in hypoxia group. VG staining revealed that the renal interstitial fibrosis was found in hypoxia group, which was significantly alleviated by swimming exercise. CONCLUSION: The levels of UII and GPR14 increase in the kidneys of the rats with hypoxic tubulointerstitial fibrosis. Moderate swimming exercise alleviates the tubulointerstitial fibrosis induced by hypoxia and decreases the expression of UII.