THE EFFECTS OF BRANCHED-CHAIN AMINO-ACID INFUSION ON PAIN PERCEPTION AND PLASMA-CONCENTRATIONS OF MONOAMINES

Infusions of branched chain amino acids (BCAA) have been shown to have several CNS-mediated effects including antinociceptive action. We inv estigated the effects of BCAA infusion on pain perception, respiratory control, and plasma monoamine concentrations. Six healthy female volu nteers were given in a double-blind, random, crossover design an 8-h i nfusion (1.75 ml/kg/h) of either (a) Ringers lactate, (b) conventional 4% amino acid solution, or (c) 4% BCAA solution with intervals of at least 48 h. Respiratory control was evaluated with continuous capnogra phy. Pain perception was measured using dental dolorimetry for sharp p ain, and pain transmitted by afferent C-fibers was evaluated with tour niquet test. Changes in vigilance were measured using critical flicker fusion technique. Evaluations were made for baseline, and after 2.5, 5, and 8 h. Plasma samples were collected at the same time points for amino acid and monoamine analysis. BCAA infusion resulted in significa nt increases of plasma concentrations of all BCAAs, with a simultaneou s decrease in concentrations of aromatic amino acids. Of the measured monoamines and their metabolites dihydroxyphenylacetic acid (DOPAC) de creased, showing significant treatment effect for BCAA. Despite these changes no significant effect of BCAAs on respiratory control, vigilan ce, or pain perception was observed. In conclusion, despite significan t changes in plasma concentrations of both amino acids and DOPAC, BCAA infusion did not show any clinically relevant antinociceptive effect. (C) 1998 Elsevier Science Inc.