Relationship of Juxtaglomerular Apparatus

IN A SYMPOSIUM devoted to angiotensin, it is appropriate to consider briefly the juxtaglomerular apparatus. Angiotensin makes its appearance in the body as a direct result of the proteolytic action of renin, and there is considerable evidence to support the hypothesis that all the renin in a kidney comes from the juxtaalomerular apparatus. Before reviewing this evidence, the anatomy of the juxtaglomerular apparatus should be considered. It consists of 2 separate cell types, the granular cells and the macula densa cells. The granular juxtaglomerular cells actually lie within the medial layer of the afferent glomerular arteriole. They have small, uniform-sized granules in the cytoplasm, which can be clearly stained with Bowie 's stain1 or with osmic acid.2 When examined with the electron nmicroseope, these cells are seen to have a rich endoplasmic reticulum with an abundanee of RNA granules, a Golgi apparatus, and their specific cytoplasmic secretory granules.2 When there are abundant granules in the cytoplasm, these cells have all the appearances of actively secreting cells. One side of the granular cell abuts the intimal layer of the afferent arteriole. On the other side, the border of the cell may interdiaitate with the border of the macula densa cells. The macula densa consists of specialized cells which are part of the wall of the distal convoluted tubule. Their stainling characteristics are different from tlle usual epithelial cells lining the distal tubule. The macula densa cells are always at the very first part of the distal tubtule and are always in close proximity to the vascular pole of the glomerulus of their particular nephron. As mentioned above,