Effects of dietary histidine and methionine loading in rats with a portacaval shunt.

To elucidate disturbances of brain amine metabolism in hepatic coma, the effects of dietary histidine and methionine loading on the brain levels of amino acids and transmitter amines and on behavior were examined in rats with a portacaval shunt (PCS rats). Surgical construction of a portacaval shunt exaggerated the increase in brain histamine caused by dietary histidine loading 4 weeks after operation. Although the marked increase in the brain level of methionine itself did not affect on the brain levels of catecholamines, serotonin, and histamine, brain level of 5-HIAA was decreased in PCS rats on methionine-enriched diet. Diminished spontaneous activity was observed in PCS rats on either diet, which could not be related to the disturbance of brain amine metabolism caused by excess histidine and methionine. These results indicated that histamine was involved in the derangement of brain amine metabolism in PCS rats, and that direct effect of dietary methionine loading on the brain levels of transmitter amines was not observed in PCS rats. The etiological relation of these substances to hepatic coma should be further investigated.