Control of glomerular function by juxtaglomerular apparatus

黄斑致密体（macula densa， MD）感知管状液中NaCl浓度的变化，从而控制肾小球传入小动脉（glomerular afferement arteriole, Af-Art）的阻力，这种现象被称为管肾小球反馈（tubuloglomerular feedback， TGF）。在与亨利福特医院高血压研究部的o . a .卡雷特罗的合作下，该项目。研究者（SI）使用同时微灌注分离Af-Art和MD的体外制剂直接研究TGF。血管紧张素II （Ang II）在tgf中的作用当MD处NaCl浓度升高时Af-Art收缩。这预示着高盐摄入会导致GFR下降。然而，在正常受试者中，高盐摄入会导致GFR轻微升高。这种悖论可以通过TGF敏感性的重置来解释，据报道Ang II在其中起着至关重要的作用。我们确实观察到，在没有Ang II的情况下，增加MD处的NaCl浓度对Af-Art的收缩作用比存在Ang II时要小。腺苷（Ado）在TGF中的作用近期研究表明，Ado在TGF中发挥作用。我们观察到一种ado A受体拮抗剂可以替代高NaCl诱导的Af-Art收缩。在Af-Art灌注液中加入低浓度ado （10^<-8>M）对基底直径没有影响，但可以大大增强tgf介导的Af-Art收缩。另一方面，MD灌注液中添加的ado （10^<-8>-10^<-6>M）无论NaCl浓度高或低，对Af-Art直径均无影响。本研究提示肾小球旁间质ado A_1受体在TGF中起重要作用。

The macula densa (MD) senses the change in NaCl concentration in the tubular fluid and thereby controls the resistance of the glomerular afferent arteriole (Af-Art), a phenomenon called the tubuloglomerular feedback (TGF). In collaboration with O.A.Carretero at Hypertension Research Division of Henry Ford Hospital, the project. Investigator (SI), studied the TGF directly using an in vitro preparation in which both isolated Af-Art and the MD were microperfused simultaneously.Role of Angiotensin II (Ang II) in the TGFWhen NaCl concentration at the MD is elevated the Af-Art constricts. This predicts that the GFR would decline under high salt intake. However, in normal subjects, high salt intake results in slightly increased GFR.This paradox could be explained by ressetting of the sensitivity of TGF,in which Ang II reportedly plays a rucial role. We indeed observed that increasing the NaCl concentration at the MD induces less constriction of the Af-Art in the absence than in the presence of Ang II.Role of Adenosine (Ado) in the TGFRecent studies indicate that ado plays a role in the TGF.We observed that an ado A receptor antagonist altenuates the Af-Art constriction induced by high NaCl at the MD.A low concentration of ado (10^<-8>M) added to the Af-Art perfusate had no effect on basal diameter but greatly augmented the TGF-mediated Af-Art constriction. On the other hand ado (10^<-8>-10^<-6>M) added to the MD perfusate had no effect on Af-Art diameter whether NaCl concentration of the MD perfusate was high or low. This study suggest ado A_1 receptor in the juxtaglomerular interstium is important in TGF.