Morsing P, Velazquez H, Ellison D, Wright F S
Department of Internal Medicine, Yale University, New Haven, CT.
Acta Physiol Scand. 1993 May;148(1):63-8. doi: 10.1111/j.1748-1716.1993.tb09532.x.
Cell-cell contact between the macula densa and the glomerular arterioles is is thought to provide the information pathway for the tubuloglomerular feedback (TGF) mechanism. When concentrations of sodium and chloride in the macula densa segment are increased, a signal is transmitted through the extraglomerular mesangium to contract the afferent arteriole. In addition, some observers have described a second region of contact between a later part of the distal tubule and the afferent arteriole of the same nephron. In this region the connecting tubule (CNT), and sometimes nerves that make contact with the cells of this CNT, were found. This arrangement gives another potential tubular segment, besides the macula densa plaque, in which the composition of tubular fluid may regulate glomerular dynamics. The present study was designed to investigate whether interrupting flow in the distal tubule downstream from the macula densa would influence the TGF mechanism. TGF was examined in rats by orthograde microperfusion, before and after blockade of the distal nephron with castor oil. Two variables were measured: maximum decrease in stop-flow pressure (delta Psf), and perfusion rate which elicits half-maximal decrease in delta Psf (V1/2). The fluid arriving at the blocking point was collected into a micro-pipette. The results show a significant increase in V1/2 from 19 to 25 nl min-1 after 30 min of blockade. In conclusion the results support a role of the distal nephron in the control of the TGF mechanism.
致密斑与肾小球小动脉之间的细胞间接触被认为是管球反馈（TGF）机制的信息传递途径。当致密斑段的钠和氯浓度升高时，信号通过球外系膜传递，使入球小动脉收缩。此外，一些观察家描述了远端小管后半部分与同一肾单位的入球小动脉之间的第二个接触区域。在这个区域发现了连接小管（CNT），有时还发现了与该CNT细胞接触的神经。这种排列除了致密斑之外，还提供了另一个潜在的肾小管节段，其中肾小管液的成分可能调节肾小球动力学。本研究旨在探讨阻断致密斑下游远端小管的血流是否会影响TGF机制。在用蓖麻油阻断远端肾单位前后，通过顺行微灌注在大鼠中检测TGF。测量了两个变量：停流压力的最大降低值（δPsf），以及引起δPsf降低一半最大值的灌注率（V1/2）。到达阻断点的液体被收集到微量移液器中。结果显示，阻断30分钟后，V1/2从19 nl min-1显著增加到25 nl min-1。总之，结果支持远端肾单位在TGF机制控制中的作用。
