Nature of the renal hemodynamic action of amino acids in dogs.

Anesthetized dogs were used to study the nature of the renal hyperemia and hyperfiltration ascribed to amino acids. Intravenous (n = 6) or intraportal venous (n = 6) infusion of a solution of three metabolizable amino acids [serine, alanine, and proline (SAP) approximately 0.051 mmol.kg-1.min-1] elevated renal blood flow (RBF) and glomerular filtration rate (GFR) by a similar amount (30%) over the same time course (60 min). Yet, direct intra-arterial infusion of SAP into the kidney at either approximately 0.0051 or 0.051 mmol.kg-.min-1 (n = 12) failed to significantly elevate either RBF or GFR over 60 min. A transient increase in RBF (approximately 13%) was, however, noted by minute 15 of the infusion. Unlike SAP, intraportal venous infusion of a physiological dose of branched-chain amino acids (valine, leucine, and isoleucine, approximately 0.0195 mmol.kg-1.min-1, n = 6) failed to elevate either RBF or GFR over 60 min. By comparison, either intravenous or intraportal venous infusion of SAP at approximately 0.020 mmol.kg-1.min-1 (n = 12) elevated renal hemodynamics by approximately 14% over 60 min. The data suggest that the liver does not directly mediate amino acid-induced increases in renal hemodynamics but that some other intermediary step activated following amino acid administration may be necessary before the renal hyperemia and hyperfiltration ascribed to amino acids are manifested in anesthetized dogs.