Transporter-mediated Prostaglandin E2 Elimination across the Rat Blood-brain Barrier and Its Attenuation by the Activation of N-methyl-D-aspartate Receptors

Prostaglandin (PG) E2 is involved in neuroinflammation and neurotoxicity, and the cerebral PGE2 concentration is increased in neurodegenerative diseases. Because the intracerebral concentration of L-glutamate (L-Glu) is reported to be also elevated in neurodegenerative diseases, it has been proposed that L-Glu affects PGE2 dynamics in the brain, and thus exacerbates neural excitotoxicity. The purpose of this study was to investigate the effect of intracerebral L-Glu on PGE2 elimination across the blood-brain barrier (BBB) in rats by using the intracerebral microinjection technique. [3H]PGE2 injected into the cerebral cortex was eliminated from the brain in rats, and the apparent brain-to-blood [3H]PGE2 efflux clearance was found to be 60.1 μL/(min·g brain). Intracerebral pre-administration of 50mM L-Glu significantly inhibited [3H]PGE2 elimination across the BBB and this L-Glu-induced inhibition was abolished by co-administration of an intracellular Ca2 + chelator. The intracellular Ca2 + concentration is reported to be increased via N-methyl-D-aspartate (NMDA)-type L-Glu receptors (NMDAR) and [3H]PGE2 elimination was attenuated by intracerebral pre-administration of a mixture of NMDA and D-serine. Moreover, the co-administration of antagonists of NMDAR with L-Glu abolished the attenuation of PGE2 elimination induced by intracerebral L-Glu administration. These results suggest that L-Glu attenuates BBB-mediated PGE2 elimination via NMDAR-mediated processes.