Effect of ethanol on plasma amino acids and related compounds of stressed male rats

Plasma amino acid levels in rats are known to be affected by ethanol or by immobilization stress. This paper investigated the effect of ethanol on plasma amino acid levels of stressed rats. Rats received ethanol (2 g/kg, IP) 15 minutes prior to a 30-min immobilization period. Blood samples were obtained from individual rats before, during and after stress. Ethanol lowered the concentration of most plasma amino acids (AA) or related compounds in stressed rats (e.g., aspartic acid, threonine, serine, glycine, alanine, valine, tyrosine, phenylalanine, tryptophan). Some compounds remained unaffected (e.g., taurine, cystine, ethanolamine and methylhistidines) and one (phosphoethanolamine) increased initially. A comparison of the effects of ethanol on plasma AA and related compounds in resting and stressed rats shows similarities and differences. In general, ethanol tends to change the concentrations of these compounds away from normal levels in nonstressed rats, whereas in stressed rats, ethanol tends to antagonize stress-induced changes. This study shows that ethanol can affect individual AA and related compounds differently in nonstressed and stressed rats and that ethanol reduces stress-induced changes. The latter finding supports the "tension-reduction hypothesis" of ethanol.