Metabolism of kinins and angiotensins in the isolated glomerulus and brush border of rat kidney

Abstract

In order to localize the activities of kallikrein, kininase, angiotensin I converting enzyme, and angiotensinase in the kidney, rat kidneys were homogenized and glomeruli and brush border were isolated. The yield and purity of glomeruli preparations were high. The similarity of the structure of the isolated glomeruli in situ was established by scanning and transmission electron microscopy and freeze-fracture. The morphology of isolated brush border of proximal tubules was compared to brush border in situ. Isolated brush border, devoid of core material, retained its converting enzyme, kininase, and angiotensinase activity confirming our previous findings that these enzymes are bound to plasma membrane. Isolated glomeruli contained little or no kallikrein. In addition, compared to renal brush border, renal glomeruli contained a relatively low concentration of kininase, angiotensin I converting enzyme, and angiotensinase. The results of these experiments support the idea that the brush border of the proximal tubule is the major site of inactivation of kinins and angiotensins and that renal kallikrein enters the tubular filtrate distal to the glomeruli and proximal tubule.