[Biochemical and pathophysiological aspects of hyperammonaemia (author's transl)]

Pathological changes in cobalt-supplemented and non-supplemented twin lambs in relation to blood concentrations of methylmalonic acid and homocysteine

In a controlled field study of three years' duration we evaluated the effect of cobalt supplementation on pathological changes in cobalt/vitamin B12-deficient Texel twin lambs grazing the same cobalt-deficient pasture. Semi-quantitative evaluation of the histopathology of liver and brain was done on 44 sets of twins. Pathological changes were related to blood concentrations of vitamin B12, methylmalonic acid, and homocysteine. Lesions were mainly confined to the liver and brain. Acute hepatic changes were characterized by steatosis, hepatocytic degeneration, and single cell necrosis. Chronic changes consisted of bile duct proliferation, the presence of ceroid containing macrophages, and fibrosis in the portal triads. Many non-supplemented lambs showed polymicrocavitation and Alzheimer type II reaction in the brain. Polioencephalomalacia was observed in three non-supplemented lambs but was regarded as a secondary lesion. Our results indicate that the main lesions found in cobalt/vitamin B12-deficient lambs are acute and chronic hepatitis. These lesions were associated with low concentrations of vitamin B12 and high concentrations of methylmalonic acid and homocysteine in the blood. The liver lesions were also associated with polymicrocavitation of the brain, probably as morphological evidence of hepatoencephalopathy.

Effect of ammonia on plasma and cerebrospinal fluid amino acids in dogs with and without portacaval anastomoses

To elucidate the possible connection between ammonia-induced changes of plasma and cerebrospinal fluid (CSF) amino acid levels and the development of hepatic encephalopathy in dogs, beagle dogs were given an ammonium acetate infusion both before and following portacaval shunt (PCS). During ammonia-induced coma and after recovery in the dogs prior to PCS the plasma and CSF concentrations of most amino acids were decreased. Following PCS the plasma and CSF concentrations of the aromatic amino acids (AAA), phenylalanine and tyrosine, increased and the levels of the branched chain amino acids (BCAA), valine, leucine, and isoleucine, decreased during ammonia-induced coma. The CSF/plasma molar ratio for the AAA exhibited a marked increase after recovery as compared to the value during coma in the Eck-fistula dogs. With respect to the AAA, no correlation was observed between signs of neurologic impairment in the animals and the following parameters: glutamine and methionine levels of CSF, and the plasma molar ratio (Formula: see text). The data obtained do not support the hypothesis that high concentrations of phenylalanine and tyrosine in the brain may be primarily responsible for altered neurotransmission leading to the development of hepatic encephalopathy.