Effects of amino acid infusion and renal failure on the uptake and release of amino acids by the dog kidney.

Net production and utilization (Qmet) of amino acids and ammonia were assessed in the left kidney of 11 normal and eight chronically uremic female dogs. Studies were conducted at the end of two 120-min infusions, first with half-normal saline and then with amino acids which increased plasma concentrations to postprandial levels. In the normal dogs, Qmet for a number of amino acids and ammonia was significantly positive (i.e., net production) or negative (i.e., net utilization). Qmet became more negative with the amino acid infusion. In the uremic dogs, Qmet for amino acids and ammonia was qualitatively similar to normal and tended to change in the same direction with the amino acid infusion. Although the absolute values for Qmet were usually less in the uremic dogs, with the amino acid infusion their mean fractional Qmet (Qmet/creatinine clearance) was often greater. A substantial proportion of the infused amino acids was removed by the kidney) in both groups of dogs. In the uremic dogs, there was evidence for preservation of glomerular-tubular balance between the filtered load of amino acids and tubular reabsorption. Data also suggest that the kidney may release sufficient quantities of certain amino acids into renal venous blood (e.g., serine) to affect the plasma levels. These findings indicate that the dog kidney may make an important contribution to total synthesis or metabolism of certain amino acids by the body and may also affect plasma concentrations of some amino acids. During amino acid infusion, the kidney plays a major role in removal of the added amino acids. In renal failure these functions are decreased, but compared to the fall in glomerular filtration rate, they are relatively well preerved.