高盐饮食上调肾局部肾素-血管紧张素系统参与大鼠高血压肾损害的发生

目的：探讨肾脏局部肾素-血管紧张素系统（renin-agiotensin system，RAS）在高盐诱发大鼠高血压及其肾损害发病机制中的作用。方法：8周龄雄性Wistar大鼠随机分为3组：对照组（NS，n=9），普通饲料喂养；高盐组（HS，n=9），含8%（质量分数）NaCl的高盐饲料喂养；高盐饮食+氯沙坦组（HS+L，n=9），高盐饲料喂养同时每日给予氯沙坦20 mg/kg灌胃。实验共6周，期间每2周监测血压和24 h尿蛋白，6周后处死大鼠，放射免疫法测定血浆、肾脏匀浆以及尿液的肾素活性、血管紧张素Ⅱ水平，Real-time PCR、免疫组织化学染色分别检测肾脏血管紧张素原（angiotensinogen，AGT）mRNA、蛋白表达水平，ELISA测定血、肾皮质匀浆液以及尿AGT水平。结果：与NS组相比，HS组大鼠第2周始血压显著升高［（156±2） mmHg vs. （133±3） mmHg （1 mmHg=0.133 kPa）, P<0.05）］，第6周时尿蛋白显著增加［（14.07±2.84） mg/24 h vs. （7.62±3.02） mg/24 h， P<0.05］；HS+L组与HS组大鼠血压差异无统计学意义（P>0.05），但第6周时HS+L组尿蛋白比HS组显著降低［（9.69±2.73） mg/24 h vs. （14.07±2.84） mg/24 h， P<0.01］。与NS组相比，HS组血浆肾素活性、AGT和血管紧张素Ⅱ（angiotensin Ⅱ，ANGⅡ）水平无显著变化（P>0.05），肾皮质肾素活性、AGT 和ANGⅡ水平均显著升高（P<0.05），尿AGT和ANGⅡ排泄率均显著升高（P<0.05）；与HS组相比，HS+L组大鼠血浆肾素活性、AGT和ANGⅡ水平均显著升高（P<0.05），肾皮质肾素活性、ANGⅡ和AGT水平均显著降低（P<0.05），尿AGT和ANGⅡ排泄率均显著降低（P<0.01），尿AGT排泄率与肾皮质AGT水平呈显著正相关（P<0.05）。结论：高盐可能通过上调肾脏局部RAS的表达参与大鼠的肾损害，尿AGT排泄率可能反映肾脏局部RAS激活的程度。

Up-regulation of intrarenal renin-agiotensin system contributes to renal damage in high-salt induced hypertension rats

Objective:To test the hypothesis that in a high-salt induced hypertension in normal rats , whether the changes of intrarenal renin-agiotensin system ( RAS) play a critical role in renal damage and could be reflected by urinary angiotensinogen ( AGT ) .Methods: In the study , 27 normotensive male Wistar-Kyoto rats were divided into control group 0.3% (mass faction) NaCl in chow, n=9, NS], high-salt diet group 8% (mass faction) NaCl in chow, n=9, HS] and high-salt diet with Losartan group 8%(mass faction) NaCl in chow and 20 mg/(kg· d) Losartan in gavages, n=9, HS+L)], and were fed for six weeks .The blood pressure was monitored and urine samples were collected every 2 weeks.AGTs in plasma, kidney and urine were measured by ELISA kits .The renal cortex expression of mRNA and protein of AGT were measured by Real-time PCR and immunohistochemistry ( IHC ) .The renin activity and ANGⅡ were measured by radioimmunoassay ( RIA) kits.Results: Compared with NS, the systolic blood pressure (SBP) (156 ±2) mmHg vs.(133 ±3) mmHg, P<0.05] increased significantly at the end of the 2nd week, and the urinary protein (14.07 ±2.84) mg/24 h vs.(7.62 ± 3.02) mg/24 h, P<0.05] increased significantly at the end of the 6th week in HS.Compared with HS, there was no significant difference in SBP (P>0.05) but the proteinuria (9.69 ±2.73) mg/24 h vs.(14.07 ±2.84) mg/24 h, P<0.01] decreased significantly in HS +L.Compared with NS, there was no significant difference in the plasma renin activity , angiotensinogen and ANGⅡlevel in HS ( P>0.05), but the renal cortex renin content (8.72 ±1.98) ng/(mL· h) vs.(4.37 ±1.26) ng/(mL· h), P<0.05], AGT formation (4.02 ±0.60) ng/mg vs.(2.59 ±0.42) ng/mg, P<0.01], ANG Ⅱlevel (313.8 ±48.76) pmol/L vs.(188.9 ±46.95) pmol/L, P<0.05] were increased signifi-cantly in HS, and the urinary AGT and ANGⅡexcretion rates increased significantly (P<0.05).Com-pared with HS , the plasma renin activity , angiotensinogen and ANGⅡlevel were significantly increased (P<0.05), but the renal cortex renin content , AGT formation, ANGⅡ level significantly decreased ( P<0 .05 ) , and the urinary AGT and ANGⅡ excretion rates decreased significantly in HS +L ( P<0.05).The urinary AGT excretion rates were positively correlated with the AGT level in the renal cortex (P<0.05).Conclusion:Up-regulation of intarenal RAS may contribute to renal damage in high-salt in-duced hypertension rats .Urinary AGT may reflect the status of intrarenal RAS .