Abstract
1. Isolated cat kidneys perfused at constant pressure with blood from normal animals respond either to infusion or to injection of 0-9% NaCl (5-20 ml./150 ml. blood) by diuresis, natriuresis, a fall of the Na concentration in the urine, a fall followed by a rise in urinary Na/K and a rise in renal blood flow. The filtration fraction remains unchanged (Figs. 1, 2). 2. Kidneys perfused either with blood from intact donors at constant blood flow or with blood from hypophysectomized donors at constant pressure show no vascular response to dilution of the blood with 0 9% NaCl. Saline dilution still causes diuresis and natriuresis. The concentration of urinary Na rises, as does Na/K without an initial fall (Figs. 3, 4). 3. Kidneys perfused with blood from headless animals are unable to respond to saline loading (Fig. 6). 4. Extracts of posterior hypothalamus convert the modified response of the kidney perfused with blood from hypophysectomized animals an dilution of the blood with saline to the response given when blood from intact animals is used (Figs. 3-5). 5. Renal responses to saline loading are shown to be due to two hormones, and are dependent on the presence of an unidentified intracranial hormone, related to hypophysial hormones.