Distribution of exogenously administered renin in mouse kidney

Purified mouse submaxillary gland renin was labelled with iodine (¹²⁵I) by the chloramine-T method and this ¹²⁵I labelled renin was given to male ICR mice(6-7 wks. old), intravenously in a dose of 20 ng(2 μCi)/40 g body weight. At a specified time, the kidneys of these treated mice were excised, the radioactivity determined and the tissues immediately prepared for microscope and electron microscope autoradiography(micro-ARG and EM-ARG). Silver grains accumulated mainly at the apical site of the proximal convoluted tubules but were not identified in other areas of the nephron, including macula densa or in the arterial wall, glomeruli, and juxtaglomerular cells(micro-ARG). Silver grains were seen in the pinocytotic vesicles, vacuoles and lysosomal granules(EM-ARG). This is the first demonstration that exogenous renin is ultrafiltered through glomerular capillaries and is reabsorbed by pinocytosis in the one-third upper area of the proximal convoluted tubule.