This chapter discusses the effects of renal renin-angiotensin system (RAS). All the components of the RAS are present within the kidney, and intrarenal formation of angiotensin (Ang) II occurs independently from the systemic RAS. Intrarenal Ang II is compartmentalized such that concentrations much higher than those existing in the circulation are maintained in the renal interstitial fluid and the proximal tubular compartment. The mRNA for angiotensinogen (AGT) is present in proximal tubular cells, and the protein is secreted into the tubules to increase intratubular formation of Ang I and II. Ang II is internalized via ATi receptor-mediated mechanisms into renal cellular endosomes. Ang II also stimulates AGT mRNA, thus leading to a positive amplification mechanism and further enhancement of intrarenal Ang II. Ang II has pleiotropic actions in the kidney regulating both cortical and medullary blood flow, vascular tone of the afferent and efferent arterioles, mesangial cells, and the sensitivity of the tubuloglomerular feedback mechanism via activation of ATi receptors. At the level of the tubules, Ang II regulates the transport rate of several transport systems in proximal and distal nephron segments via the activation of luminal and basolateral ATi receptors. Collectively, the actions of Ang II regulate many aspects of renal function, including renal blood flow, glomerular filtration rate, and sodium excretion. © 2006 Elsevier Inc. All rights reserved.
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