BINDING OF THE LIGAND [H-3] MK-801 TO THE MK-801 BINDING-SITE OF THE N-METHYL-D-ASPARTATE RECEPTOR DURING EXPERIMENTAL ENCEPHALOPATHY FROM ACUTE LIVER-FAILURE AND FROM ACUTE HYPERAMMONEMIA IN THE RABBIT

Binding of the ligand [H-3]MK-801 to the MK-801 binding site of the N- methyl-D-aspartate (NMDA) receptor population on brain homogenates in rabbits was studied during experimental encephalopathy from acute live r failure and from acute hyperammonemia in the rabbit. Homogenates wer e prepared from brain cortex, hippocampus and striatum. Hepatic enceph alopathy was induced by a two-stage liver devascularization procedure and acute hyperammonemia by a prolonged ammonium-acetate infusion; rab bits receiving a sodium-potassium-acetate infusion served as controls. In these animal models extracellular brain glutamate levels are known to be elevated. However no significant alterations in the number nor the affinity of the MK-801 binding sites of the NMDA receptors were fo und during acute liver failure and acute hyperammonemia. These finding s suggest that the NMDA receptor population remains unaltered in exper imental encephalopathy from acute liver failure and acute hyperammonem ia, despite alterations in extracellular brain glutamate levels.