Effects of amino acid isomers on canine renal hemodynamics

The major objective of this study was to ascertain whether the renal hemodynamic response to amino acid infusion in dogs is stereospecific. To test this hypothesis, we examined the renal hemodynamic effects of two isomers (L and D) of an amino acid mixture of serine, alanine, and proline (SAP; 0.051 mmol.kg-1.min-1) in anesthetized dogs. Intravenous infusion of L-SAP (n = 6) significantly elevated renal blood flow (RBF) and glomerular filtration rate (GFR) by 33 +/- 3 and 30 +/- 5%, respectively, over 1 h. DL-SAP (n = 6) elevated RBF and GFR by only 14 +/- 3 and 13 +/- 3%, respectively. Yet D-SAP (n = 6) failed to elevate either RBF or GFR over 1 h. Intravenous mannitol (940 mos-mol/kg; osmotic control; n = 6) also failed to elevate renal hemodynamics. In six other dogs, intrarenal infusion of L-, but not D-, SAP marginally elevated RBF and GFR by 13 +/- 2 and 12 +/- 2%, respectively, over 1 h. Infusion of alpha-aminoisobutyric acid (0.051 mmol.kg-1.min-1; n = 6), an amino acid analogue that is cotransported with sodium but not metabolized by renal cells, elevated RBF and GFR by 22 +/- 5 and 18 +/- 6%, respectively, over 1 h. These data indicate that vascular infusion of L, but not D, isomers of amino acids elevate RBF and GFR. We therefore suggest the importance of amino acid stereospecificity in the renal vascular response to amino acid infusion in dogs.