Effects of pentobarbital and diazepam on rat plasma amino acid patterns.

Intraperitoneal injections with pentobarbital and diazepam caused an increase in the concentration of most plasma amino acids in rat. In contrast, tryptophan was significantly decreased after treatment with pentobarbital. The tyrosine level showed no change and was thus actually reduced after pentobarbital treatment in relation to the total pool of large neutral amino acids. The possibility should be considered that these changes in plasma amino acid patterns may lead to reduced transport of e.g. tryptophan and tyrosine into the brain, which in turn might retard the synthesis of monoaminergic neurotransmitters. The transport and action of several aromatic amino acids used as therapeutic agents may also be influenced.