| Objective: To investigate the renoprotective effects of angiotensinⅡtype 1 receptor antagonist (losartan) through renal up- regulated angioensin II type-2 receptors in renovascular hypertension rat . Explore the renal function of AT2-R. To appraise the effects of losartan on Na+-K+- ATPase activity and the expression of AT2-R protein of WKY rat proximal tubules (RPT) cell.Methods:Maleness SD rats were divided into sham group and 2K1C group. 2K1C group,left renal artery was partially obstructed by ligation with the residual diameter of 0.3mm. Sham group ,left and right renal artery were not touched.The two groups were delivered by direct intragastric administration with different dose losartan.After 6 weeks treatment,all animals were killed for the measurements of renal function。The expression of AT2-R protein in right kidney were deteminde by immunohistochemisty. AngII cotents in right kidney and plasma were deteminde by radio-immunoassay.Adding H2O,AngⅡ,Losartan,AngⅡ+Losartan respectively to the cultured fluid to observe the changes. Na+-K+- ATPase activity of the cultured RPT cell membranes were estimated by Na+-K+- ATPase activity test kit . The expression of AT2-R protein in RPT cell were deteminde by Western-Blot.Results:1. In renovascular hypertension rats, renal contents of Scr,BUN in plasma were decreased by 88% and 89%,respectively.2. Losartan (10,20,30mmg/Kg d-1) decreased the contents of Scr,BUN in operated group and sham operated group rats,it was more apparent in operated group rats.3. The presence of the AT2 receptor expression in non-ischemic kidney was confirmed by Immunohistochemisty. Statistical Analysis revealed 0.45–fold increased in AT2 receptor proteins compared with sham operated group rats .And losartan increased the expression of renal AT2-R.4. The contents of AngII in operated group kidney increased significantly compared with sham-operated group,whereas the contents in plasma didn,t change.Losartan not only increased the AngII cotents in non-ischemic kidney of operated group and sham operated group rats ,but also the AngII cotents in plasma,it was more apparen in plasma.5. AngII exerts a biphasic effect on Na+-K+-ATPase activity. Beginning at 10-13 M, AngII increased Na+-K+-ATPase activity in freshly isolated rat proximal tubules ,to a maximum stimulation at 10-10 M of 0.49-fold above control.Stimulation decreased progressively at concentrations above10-9 M .6. The ANG II AT1 receptor antagonist losartan blocked the stimulatory effect of ANG II at 5×10-11 M.7. Densitometric analysis of the bands revealed AngII,losartan and A+L increased the expression of AT2-R in WKY RPT cell by Western blotting, respectively increased 19.5%,35.5%,52.5% compared to control group.Conclusion:1. In renovascular hypertension rats, the expression of AT2-R protein in the contralateral, non- ischemic kidney were up-rugulated,losartan increased the expression of AT2-R protein.The contens of AngII in operated group kidney increased significantly, whereas the contents in plasma didn,t change. Losartan selectively blocked AT1 receptors, increased the AngII cotents in non-ischemic kidney and plasma, especially in plasma.2. AngII exerts a biphasic effect on Na+-K+-ATPase activity. Losartan blocked the stimulatory effect of ANG II at 5×10-11 M, had renal protective effect at cellular level.3. In the renovascular hypertension rats, the renoprotective effects of losartan were not only related to blocking AT1-R mediated physiological effect in receptor level,but also related to up-regulating and activating of AT2-R.4. AngiotensinⅡtype 1 receptor antagonist (Losartan) selectively block AT1 receptors and leave the AT2 receptors unopposed to function,leave the AT2 receptors intact, which mediates the beneficial effects and protects renal function.
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