Metabolic Factors in the Renal Response to Amino Acid Infusion

In order to investigate the renal effects of amino acids (AA) with different metabolic fate, we compared the changes in glomerular and tubular function, nitrogen metabolism and glucoregulatory hormones in 7 volunteers during two infusions, one of a complete solution of amino acids (MIX-AA), which included five AA electively metabolized at the splanchnic level, and the other of a solution containing only essential AA (EAA), which escape splanchnic metabolism. MIX-AA increased GFR and RPF (from 104 ± 6 to 122 ± 13 and from 488 ± 46 to 572 ± 34 ml/min/1.73 m 2 ), stimulated splanchnic metabolism as demonstrated by rises in urinary urea excretion (from 20.7 ± 2 to 30.6 ± 7.5 mg/min/1.73 m 2 ) and the plasma glucagon/insulin ratio (from 21.4 ± 13 to 26.7 ± 15), and caused increases in fractional excretion of AA, FeNa and free-water clearance. During MIX-AA infusion significant correlations were observed between the individual values of GFR and the urea excretion rate (r = 0.66), and between GFR modifications (ΔGFR) and the plasma glucagon/plasma insulin ratio (r = 0.40). No change in renal function, urea excretion and the glucagon/insulin ratio was observed with EAA. An intermediate splanchnic step (increased plasma glucagon/insulin ratio and ureagenesis) seems necessary in the pathway leading to the nonessential AA-induced rise in GFR; this might stimulate an ultimate intrarenal pathway (possibly involving the diluting segment) via a still undefined mechanism.