Metabolism of Insulin-I¹³¹ and Glucagon-I¹³¹ in the Kidney of the Rat

Crystalline insulin or glucagon labeled with I 131 was injected intravenously in adult male Sprague-Dawley rats under ether anesthesia. The left kidney was removed at intervals ranging from 10 seconds to 6 minutes following the injection, and radioautographs of histological sections were prepared. Radioactivity was found to be concentrated in the cortex of the kidney. At intervals less than 2 minutes after injection, radioactivity was prominent in the lumina of proximal convoluted tubules. At later intervals radioactivity tended to become more concentrated in the cells of the proximal tubules than in the lumina. The observations support the hypothesis that proteins may be filtered through the glomerular membrane and reabsorbed in the tubules.