Evidence for central hypertyraminemia in hepatic encephalopathy.

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Abstract
In mongrel dogs, the effect of end-to-side portacaval shunt on plasma, cerebrospinal fluid (CSF) and brain tyramine, tyrosine, dopamine, norepinephrine, and epinephrine were studied. It was found that the level of tyramine in plasma, CSF, and selected brain regions increased steadily after the construction of the shunts. These elevations became more pronounced when the dogs manifested symptoms of hepatic encephalopathy. In postshunted dogs with stage II and III hepatic encephalopathy, tyramine concentration in corpus striatum (1,312 +/- 371), hypothalamus (400 +/- 67.0), and midbrain (660 +/- 78.7 ng/g) was significantly (P less than 0.05) higher than the level in dogs with stage 0 and I hepatic encephalopathy and sham-operated dogs serving as controls (corpus striatum, 831 +/- 140; hypothalamus, 167 +/- 40.0; and midbrain, 132 +/- 37.4 ng/g). This was followed by a concomitant depletion of dopamine and norepinephrine in these brain regions (postshunt: dopamine 104 +/- 20.0, 3,697 +/- 977, and 105 +/- 14.1; norepinephrine 521 +/- 71.6, 81.6 +/- 13.7, and 218 +/- 31.7 ng/g; vs. sham group: dopamine 532 +/- 83.1, 8,210 +/- 1,126, and 192 +/- 35.0; norepinephrine 1,338 +/- 425, 124 +/- 21.3, and 449 +/- 89.7 ng/g) of encephalopathic dogs with portacaval shunt. Furthermore, tyramine, tyrosine, dopamine, and norepinephrine levels in plasma and CSF increased markedly as clinical features in the dogs' behavior characteristic of hepatic encephalopathy occurred, including hypersalivation, ataxia, flapping tremor, somnolence, and coma. Cerebral hypertyraminemia and a defect in sympathetic neurotransmission may contribute to the development of hepatic encephalopathy of liver disease.