Amino acid metabolism during total parenteral nutrition in healthy volunteers: evaluation of a new amino acid solution

The aim of this study was to determine the metabolism and the tolerance of a new amino acid (AA) solution administered under conditions mimicking cycl ical parenteral nutrition (PN) in humans. Eight healthy volunteers received peripheral PN for 10 h providing 10.5 mg N(.)kg(-1.)h(-1) and 2.0 kcal(.)k g(-1.)h(-1) (glucose-to-lipids ratio: 70/30%). For adaptation, a non-protei n energy intake was increased progressively for 90 min; thereafter, AA infu sion was started and maintained at a constant rate for 10 h. Plasma and uri ne concentrations of all the AAs were measured before, during and after the PN. For each given AA, the relation between plasma variations at the stead y-state and infusion rate, plasma clearance (Cl), renal clearance (Clr), re -absorption rate (Reab) and, retention rate (Reten) were determined. The ni trogen balance (DeltaN) was calculated during the PN period. The results ar e presented as means sem. All plasma AA concentrations decreased during the starting period of non-protein energy intake. The plasma AA concentrations reached a steady-state within 3 h upon AA infusion, except for glycine and lysine (6 h). At the steady state, the plasma concentrations of the infuse d AAs were closely correlated to their infusion rate (y = -18.3+1.5x, r(2) = 0.92). The plasma glutamine concentration was maintained during the PN, w hich indicates that the solution might stimulate the de novo synthesis of t his AA. When the PN was stopped, plasma levels of the AAs decreased, most o f them returning to their basal levels, or significantly below for lysine ( P < 0.05), alanine (P < 0.05), proline (P < 0.01) and glutamine (P < 0.05). No volunteer showed any adverse effect during the infusion period. DeltaN was: 0.8-3-0.5 gN/10 h. Metabolic characteristics for essential AAs were: C l < 0.51 min(-1), Clr < 1.5 ml-min(-1) Reab greater than or equal to 99%, R eten greater than or equal to 99% and for non-essential AAs: Cl < 0.61(.)mi n(-1) except aspartate (2.8 +/-0.31-min(-1)), Clr < 3ml-min(-1) except glyc ine (6.8 +/-0.7), aspartate (8.2 +/-3.5) and histidine (8.8 less than or eq ual to1.3); Reab greater than or equal to 98% except glycine (95 +/-1), asp artate (94 +/-2) and histidine (94 +/-1), Reten greater than or equal to 97 % except histidine (94 +/-1), glycine (95 +/-3). These results indicate tha t in healthy subjects, the amounts of AAs provided by the new solution were well balanced for an intravenous administration, and so were well utilized without excessive urinary excretion. The present study provides useful met abolic parameters for a further evaluation in disease. (C) 2001 Harcourt Pu blishers Ltd.