Gluconeogenesis in the Isolated Perfused Rat Kidney

The perfused rat kidney was used for a study of gluconeogenesis. The kidney was completely isolated and perfused with Krebs-Henseleit bicarbonate buffer containing 5% albumin. Perfusion flow rate and pressure remained stable for 2 to 3 hours, although the glomerular filtration rate diminished with time. The fractional reabsorption of both water and sodium was 0.92 during the 1st hour of perfusion. The rate of glucose formation from pyruvate was linear and in excess of 1 µmole per min per g of tissue. Glucose production from l-lactate was less than that from pyruvate, and the uptake of lactate was also less. Fructose was converted to glucose more readily than was dihydroxyacetone, and at approximately the same rate as pyruvate. Glucose production from l-glutamate proceeded at about the same rate as that from l-lactate. l-Alanine produced no glucose, and no alanine uptake could be detected. A mixture of amino acids, pyruvate, l-lactate, and glycerol at normal plasma concentrations supported gluconeogenesis at an initial rate of about 0.6 µmole per min per g of kidney. The rate of gluconeogenesis was sensitive to small changes in the pH of the perfusate. With either lactate, pyruvate, glutamine, or a substrate mixture of predominantly amino acids, glucose production was greater at pH 7.23 than at pH 7.64. Conversely, gluconeogenesis from glycerol and fructose was inhibited by a pH of 7.23 and increased by pH 7.64. Addition of adenosine 3',5'-monophosphate to the perfusate stimulated gluconeogenesis from lactate, pyruvate, and amino acids, but not from glycerol. Neither glucagon, epinephrine, parathyroid extract, nor vasopressin altered the rate of gluconeogenesis.