Simultaneous two-dimensional HPLC determination of free D-serine and D-alanine in the brain and periphery of mutant rats lacking D-amino-acid oxidase.

A fully automated two-dimensional HPLC system combining a microbore-ODS column and a narrowbore-enantioselective column was designed and validated, and the amounts of D-serine (D-Ser) and D-alanine (D-Ala) in various tissues and physiological fluids of Long-Evans agouti/SENDAI (LEA/Sen) rats lacking D-amino-acid oxidase (DAO) were determined. Intra- and inter-day precision was less than 4.3% and accuracy ranged between 99.9 and 104%. LEA/Sen rats were reported to lack DAO in their kidneys and expected to be a novel mutant animal lacking DAO, however, the amounts of D-amino acids in the LEA/Sen rats have not been investigated. In the present study, the intrinsic amounts of D-Ser and D-Ala, which are neuromodulators of the N-methyl-D-aspartate (NMDA) receptors, were determined in seven brain tissues, four peripheral tissues, plasma and urine of the LEA/Sen rats and compared to those of the control (Wistar and SD) rats having normal DAO activity. The levels of D-Ser in the tissues and physiological fluids of the LEA/Sen rats were significantly higher than those of the Wistar and SD rats except for the frontal brain regions. Concerning D-Ala, the amounts in the tissues and physiological fluids of the LEA/Sen rats were drastically increased compared to those of the Wistar and SD rats. These results indicate that the intrinsic amounts of D-Ser and D-Ala in the tissues of rats are regulated by DAO, and that LEA/Sen rats would be useful for the study of NMDA receptor-related diseases in which DAO is implicated.