| Objective: Tubulointerstitial fibrosis is the final common pathway to end stage renal disease. Close pathological analysis shows that functional impairment of the kidney is better correlated with the degree of renal interstitial fibrosis (RIF) damage than with that of glomerular injury in patients with CKD. The degree of RIF has high relevance to that of renal dysfunction. So renal interstitial fibrosis could often been considered as a reliable indecator in evaluating progression of kidney diseases. The mechanisms of Renal interstitial fibrosis of occurrence and development is complex, in which renal tubular epithelial myofibroblast transdifferentiation plays an important role .Erythropoietin (EPO) is an endogenous hormone produced primarily by the kidney which can control the production of erythrocytes by promoting the survival, proliferation and differentiation of marrow erythroid progenitor cell. It is widely used in treating patients with chronic renal failure anemia. It has been found in recent studies that EPO is a multifunctional cytokine, in addition to increase the oxygen supply by the regulation of erythropoietin, It also has the function of anti-apoptotic, anti-inflammatory, antioxidant, promoting angio- Genesis, cell proliferation and anti-tumor.It was studied abroad that, EPO can induce HO-1 expression to increase, decrease oxidative stress, reduce renal tubulointerstitial damage and macrophage infiltration, and exert the effects on protection of renal. If the renal tubular epithelial cell strains are cultivated in medium with the absent of HO-1, Tubular epithelial cells and smooth muscle actin expression begin to significantly increase and enhanced epithelial cell transdifferentiation.This research takes the UUO model as the object of study, observes kidney organization's pathology changes, exams routine blood, uses the immunohistochemistry to observe and discuss the expression and variety of TGF-β1`α-SMA and HO-1. and meanwhile uses the recombinant human erythropoietin, (rh-EPO) to intervene, then make a further discussion to the functions of improving the renal interstitial fibrosis and other possible systerms. It explores a sexperimental theory for preventing chronic kidney disease progress.Methods: 54 health male Wistar rats weighing 180~220g were randomly divided into 3 groups: sham-operated group (A), UUO group(B), UUO with treated rh-EPO group(C). To establish the unilateral ureteral obstructive rat model, the left ureter was ligated by 4.0 silk at two points and cut between the ligatures under 10% Chloral Hydrate anesthesia(0.8~1ml). Sham-operated rats only free the ureter, but not ligated. Rh-EPO was administrated by daily ih injections of 300IU/kg from three days before surgery until the day killed, and the same volume of saline was administrated for the controls. Each group was also randomly divided into 3, 7, 14 groups in term of the days after surgery(n=6). All rats were allowed free access to food and water. Rats were killed on days 3, 7 and 14 after surgery, then the blood was got for examination and their left kidneys were promptly taken out. Accroding to coronary palce kidneys were promptly taken longitudinal shape and half of them were fetched and were routinely fitted in 4% phosphate-buffered paraformaldehyde and paraffin embedded. Tissue sections at 5μm and 3μm were obtained. Under the light microscope, pathological changes were observed by using HE and Masson stain to calculate the area of pathological changes. The changes of hemoglobin is tested. The changes of HO-1, TGF-β1,α-SMA and their expression positions were analyzed by routine immunohistochemical method. The results were analyzed semi-quantitatively by the pathological image analysis system. All the data were analyzed by SPSS13.0 statistics software, Pvalue<0.05 was considered to have statistical significance.Results: 1 Gross observation: The rat kidneys in group A were normal like bean from the appearance; The obstruction kidneys become bigger as time went on in group B and group C since the third day after surgery. The clear and transparent seeper was obstructed in the bigger kidneys. The renal cortex become thin, the renal pelvis expanded, minor calyx oppressed and become flat. 2 HE: There was no abnormal changes in sham-operated group on 3, 7, 14 days after UUO; At the third day after the obstructive operation in group B, the renal tubles slightly expanded, there were a small number of monocyte/macrophage and lymphocyte inflammatory infiltration; the interstitial area was even widened and epithelial cells became occasionally flatting. With the time of obstruction going on, above mentioned lesion aggravated; the tubule basement membrance appeared diffuse thicken, atrophy and even collapse; there were a lot of auantic tubules in the renal cortex and extra medulla; In the interstitial area there were more monocyte/macrophage and lymphocyte inflammatory infiltration and the interstitial area was wider than before; fibrosis in the area also seemed more obvious than before. The area of the renal interstitial was significantly increased in the obstructed kidneys compared with that of group A (P<0.05); compared with B, C is improved (P<0.05). 3 Masson: The renal interstitial area in kidney of group C significantly decreased compared with that of group B (P<0.05), but increased compared with that of group A (P<0.05) by Masson stain; 4 the difference of Hemoglobin in different groups had no statistical significance(P>0.05); 5 By immunohistological staining, we knew that the expression of HO-1,α-SMA, TGF-β1 were at low level of in group A; Whereas in group B and C, the expression of HO-1 was highter than those in group A and decreased gradually. And the level of HO-1 in group C was higher than that in group B at the same time point(P<0.05). The expression of TGF-β1. andα-SMA increased gradually in group B and C, and peaked at day 14. The level of TGF-β1 andα-SMA in group C was lower than that in group B at the same time point and obviously higher than that in group A(P<0.05). Rats in group B showed more significant difference between any two of the three groups and between any two time points within a group (P<0.05). Only rats in group A revealed constant levels in these three factors in different time points (P>0.05).Conclusion: 1 Expression ofα-SMA and TGF-β1 up-regul -ation but HO-1 down-regulation in kidney of UUO rat; 2 EPO can improve changes of histomorphology in kidney of UUO rat, lighten renal tubule extension, mononuclear-lymphocyte infiltration and deposition of collagen in renal interstitium. At the same time, it does not change the normal hemoglobin; 3 EPO makes the expression ofα-SMA and TGF-β1 up-regulation and HO-1 down-regulation in kidney of UUO rat to suppress renal tubular epithelial cell transdifferentiation, postpone fibrosis of renal interstitium.
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