Pyridoxal 5'-phosphate levels in brain after treatments which impair cerebral glucose metabolism.

Pyridoxal 5'-phosphate (PLP) concentrations were measured in brains of rats to determine whether a deficiency of this coenzyme was a common feature in hepatic coma, ethanol intoxication, and in animals treated with L-dopa or with 5-hydroxytryptophan (5-HTP) alone or with inhibitors of MAO or of L-aromatic amino acid decarboxylase. These treatments have been shown previously to be associated with reduced conversion of glucose to amino acids in brain. Cerebral PLP concentrations were reduced after some of these treatments, notably injection of ethanol, or L-dopa alone or with beta-phenylisopropylhydrazine, an inhibitor of MAO, or of 5-HTP together with N-[beta-(chlorophenoxy)ethyl]cyclopropylamine hydrochloride, Lilly 51641, another MAO inhibitor. However, in other circumstances where inhibition of conversion of glucose to amino acids has been shown (treatment with 5-HTP, or with Lilly 51641 or with [N-(D,L-seryl)-N'-2,3,4-trihydroxybenzyl]hydrazine, an inhibitor of L-aromatic amino acid decarboxylase, together with L-dopa or with 5-HTP), PLP levels in brain were unchanged, or were increased (in hepatectomized rats).