METABOLIC FACTORS IN THE RENAL RESPONSE TO AMINO-ACID INFUSION

In order to investigate the renal effects of amino acids (AA) with dif ferent metabolic fate, we compared the changes in glomerular and tubul ar function, nitrogen metabolism and glucoregulatory hormones in 7 vol unteers during two infusions, one of a complete solution of amino acid s (MIX-AA), which included five AA electively metabolized at the splan chnic level, and the other of a solution containing only essential AA (EAA), which escape splanchnic metabolism. MIX-AA increased GFR and RP F (from 104 +/- 6 to 122 +/- 13 and from 488 +/- 46 to 572 +/- 34 ml/m in/1.73 m(2)), stimulated splanchnic metabolism as demonstrated by ris es 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 2 6.7 +/- 15), and caused increases in fractional excretion of AA, FeNa and free-water clearance. During MIX-AA infusion significant correlati ons were observed between the individual values of GFR and the urea ex cretion rate (r = 0.66), and between GFR modifications (Delta GFR) and the plasma glucagon/plasma insulin ratio (r = 0.40). No change in ren al function, urea excretion and the glucagon/insulin ratio was observe d 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 u ltimate intrarenal pathway (possibly involving the diluting segment) v ia a still undefined mechanism.