Studies of the functional role of the intrarenal renin-angiotensin system

In the kidney, renin is synthesized and stored by specialized cells in the afferent arteriole, the juxtaglomerular cells, which are derived from smooth muscle cells. The juxtaglomerular cells are more highly differentiated than ordinary smooth muscle cells and contain numerous-bound granules, the sites where renin is stored and presumably synthesized. Specialized granular epithelial cells situated in the angle between the afferent and efferent arterioles and the distal tubule comprise the macula densa. Collectively, the granular cells of the macula densa and in the wall of the afferent arteriole are termed the juxtaglomerular apparatus [1]. It has been shown repeatedly that all components of the renin-angiotensin system are present within the kidney in close association with the component structures of the juxtaglomerular apparatus [2-4]. Thus, it has been proposed that angiotensin may be formed intrarenally, and that angiotensin exerts a controlling influence on renal function through the unique anatomical structure of the juxtaglomerular apparatus, independent of changes in the systemic renin-angiotensin system. In this article, we will assess the evidence for a functional role of the intrarenal renin-angiotensin system acting as a local hormonal system in the control of renal function.