Uptake and release of amino acids by normal and remnant kidneys: studies in the isolated perfused rat kidney.
In order to evaluate the capacity of normal and remnant kidneys to take up and release amino acids when plasma concentrations are increased above normal levels, we have determined the simultaneous net uptake or release of eight representative amino acids using the isolated perfused rat kidney model. Eight normal and five partially infarcted kidneys from Sprague-Dawley rats were perfused with Krebs-Ringer's bicarbonate buffer containing glucose 8 g/100 ml albumin and amino acids at concentrations approximately 10 times above normal plasma levels. Urine was collected every 15 min for 75 min, and perfusate samples were obtained at the midpoint of each urine collection. Amino acids were measured by gas-liquid chromatography. During perfusion, there was substantial net utilization of asparate, proline, alanine, and glycine by normal kidneys. In remnant kidneys the net uptake of amino acids tended to be lower than that of the normal kidneys. The fractional excretion of most amino acids by remnant kidneys was significantly higher than that of controls. These studies demonstrate the substantial capacity of the kidney to take up or release amino acids when presented with an increased load. The findings suggest that the fractional reabsorption of amino acids by residual nephrons of remnant kidneys is decreased.