Tubule-vascular feedback in renal autoregulation

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American journal of physiology. Renal physiology


Afferent arteriole (Af-Art) diameter regulates pressure and flow into the glomerulus, which are the main determinants of the glomerular filtration rate (GFR). Thus, Af-Art resistance is crucial for sodium filtration. Af-Arts play a role as integrative centers, where systemic and local systems interact to determine the final degree of resistance. The tubule of a single nephron contacts an Af-Art of the same nephron at two locations: in the transition of the thick ascending limb to the distal tubule (macula densa) and again in the connecting tubule. These two sites are the anatomical basis of two intrinsic feedback mechanisms: tubule-glomerular feedback (TGF) and connecting tubule-glomerular feedback (CTGF). The cross-communications between the tubules and Af-Arts integrate tubular sodium and water processing with the hemodynamic conditions of the kidneys. TGF provides negative feedback that tends to avoid salt loss, and CTGF provides positive feedback that favors salt excretion by modulating TGF (resetting it) and increasing the GFR. These feedback mechanisms are also exposed to systemic modulators (hormones and the nervous system); however, they can work in isolated kidneys or nephrons. The exaggerated activation or absence of any of these mechanisms may lead to disequilibrium in salt and water homeostasis, especially in extreme conditions (e.g., high-salt diet/low-salt diet) and may be part of the pathogenesis of some diseases. In this review, we focus on molecular signaling, feedback interactions and the physiological roles of these two feedback mechanisms.

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ePub ahead of print