A technique for perfusing the isolated rat kidney is described. It is primarily designed for the study of renal metabolism but is also suitable for studying some aspects of the secretory function; this was normal with respect to minimal glucosuria. The glomerular filtration rate as measured by creatinine clearance was lower than in vivo and slowly decreased with time. 2. Gluconeogenesis from a variety of precursors was rapid and similar to that in kidney-cortex slices, in contrast with liver where the perfused organ is more effective than slices. Whereas the maximal rates of gluconeogenesis from glycerol and pyruvate were similar in liver and kidney, the rates from succinate, malate and fumarate were 14-20 times, and those from glutamate and aspartate about three times, as high in the kidney. 3. The oxygen consumption of the perfused organ was about twice that of cortex slices, presumably because of the secretory work done in the perfused organ but not in slices. 4. The rate of acetoacetate oxidation was about the same in the perfused organ and in slices but, because of the higher rate of oxygen consumption, the percentage contribution of acetoacetate to the fuel of respiration was lower in the perfused organ. The results suggest that acetoacetate can supply energy for the basal requirements and for gluconeogenesis but not for the secretory work. 5. Glutamine was formed at a high rate from glutamate and at a lower rate from aspartate. The high rates indicate that, in the rat, the kidney is a major source of body glutamine.
