大鼠侧脑室注射血管紧张素Ⅱ抑制近曲小管Na^+,K^+-ATPase活性

Intracerebroventricular administration with angiotensinⅡ Inhibits proximal convoluted tubules Na^+,K^+-ATPase activity in rats

目的探讨脑内血管紧张素Ⅱ(angiotensinⅡ,AngⅡ)对肾小管Na+,K+-ATPase活性的作用及作用途径。方法雄性SD大鼠,麻醉下侧脑室注射人工脑脊液或AngⅡ(100ng),或先注射AngⅡ的1型受体(AT1)拮抗剂Losartan(10μg)后再注射AngⅡ(100ng)。注射后30min取血,放射免疫分析法测定血清内源性洋地黄样物质(endogenousdigitalis-likesubstance,EDLS)水平;立体显微镜下手工微分离单根近曲小管,电镜鉴定;以[γ-32P]ATP与近曲小管孵育后用液闪计数器测定标记磷酸的方法计算出近曲小管Na+,K+-ATPase活性。结果与侧脑室注射aCSF的结果比较,在侧脑室注射AngⅡ后30min,血清EDLS水平显著升高(62.95±9.80vs.42.55±7.91pg/ml,P<0.05);近曲小管Na+,K+-ATPase活性显著降低(1285±157vs.2105±176pmolPi/mm/h,P<0.05);近曲小管Na+,K+-ATPase活性下降幅度与血清EDLS升高幅度呈负相关,(r=-0.918,P<0.05);而Losartan预处理侧脑室再注射AngⅡ后30min,血清EDLS水平和近曲小管Na+,K+-ATPase活性均无显著变化。结论脑内的AngⅡ通过AT1受体介导,促进EDLS释放,从而抑制肾小管的Na+,K+-ATPase活性。

Objective The present study is designed to investigate the effect and the of administration of angiotensin II (Ang II) into a lateral ventricle on the Na^+,K^+-ATPase activity of the proximal convoluted tubules and its approach in rats.Methods Experiments were carried out on anesthetized male SD rats. A stainless steel tube was planted accurately in an intracerebroventricular for microinjection. A lateral ventricle was administrated in vivo respectively with artificial cerebrospinal fluid(aCSF,5μl) or AngII(30ng),or an AngII antagonist(losartan,10μg) and AngII(30ng) successively. Blood samples, kidneys and brains were collected at 30min after Intracerebroventricular administration. The levels of serum endogenous digitalis-like substance(EDLS),and plasm AngII were assessed with radioimmunoassay (RIA). The proximal convoluted tubules were microdissected freehand, and were identified with electron microscope. Na^+,K^+-ATPase activity of proximal convoluted tubules were assessed after incubation with [γ- ~ 32 P]ATP using a radiochemical assay based on the measurement of Pi released from [γ- ~ 32 P]ATP by liquid scintillation counter(LSC).Results Microinjection of AngII intracerebroventricular produced a significantly increase in serum EDLS level than in control rats (62.95±9.80 vs. 42.55±7.91pg/ml,p<0.05).Na^+,K^+-ATPase activity of proximal convoluted tubules significantly decreased in AngII group rats than control rats(1285±157 vs. 2105±176 pmol Pi/mm/h, P<0.05). There was a negative linear correlation between serum EDLS level and the Na^+,K^+-ATPase activity of proximal convoluted tubules in the rat that an intracere broventricular were administrated with AngII (r=-0.908,P<0.05). In the rats with intracerebroventricular pretreatment with losartan before microinjection of AngII, however, there was not significant difference in the Na^+,K^--ATPase activities in proximal convoluted tubules or EDLS level in serum compared with aCSF group.Conclusions It is conclused that inhibition of the Na^+,K^+-ATPase activity in proximal convoluted tubules as a result of AngII in an intracerebroventricular is mediated by AT1 receptors. The increase in EDLS release may play an important role in this inhibition.