Effect of amino acid infusion on renal hemodynamics in humans: A dose- response study

We evaluated the dose-response relationship between the plasma amino acid (AA) concentration and renal hemodynamics in eight normal subjects. After an overnight fast, a balanced 10% AA solution was infused for 180 min at five separate infusion rates: 0.5 (group 1), 1.0 (group II), 2.0 (group III), 4.0 (group IV), and 6.0 (group V) ml · kg^-1 · min^-1 on separate days. Basal plasma AA concentration was 1.87 ± 0.1 mmol/l and increased to 2.26 ± 0.1 (group I), 2.66 ± 0.2 (group II), 3.79 ± 0.5 (group III), 5.81 ± 0.4 (group IV), and 7.41 ± 0.4 mmol/l (group V). Basal glomerular filtration rate (GFR) and renal plasma flow (RPF) averaged 95 ± 4 and 476 ± 29 ml · 1.73 m^-2 · min^-1, respectively, and rose to 98 ± 5 and 506 ± 40 (group I) [P = not significant (NS)], 102 ± 3 and 533 ± 30 (group II) (P < 0.05 vs. basal), 110 ± 4 and 567 ± 29 (group III), 115 ± 7 and 610 ± 55 (group IV), and 117 ± 7 and 614 ± 66 ml · 1.73 m^-2 · min^-1 (group V) (P = NS vs. group IV). Basal plasma glucagon concentration averaged 68 ± 10 pg/ml and increased to 74 ± 10 (group I), 83 ± 11 (group II) (P < 0.05 vs. basal), 100 ± 14 (group III), 121 ± 14 (group IV), and 229 ± 35 pg/ml (group V) (P < 0.01 vs. basal). Increases in plasma growth hormone (GH) and insulin levels were observed only during groups IV and V. Plasma insulin- like growth factor I (IGF-I) did not change significantly during AA infusion. These results indicate the following: 1) increases in plasma AA concentrations within the physiological range cause a dose-related rise in GFR and RPF (r = 0.94, P < 0.001); 2) pharmacological increases in plasma AA levels are not associated with any further rise in GFR and RPF above that observed with physiological hyperaminoacidemia; and 3) within the physiological range the increases in GFR and RPF are closely correlated with the elevation in plasma glucagon concentration (r = 0.98, P < 0.001) but not with changes in insulin, GH, or IGF-I levels.