BIOCHEMTCAL CHANGES IN THE BRAIN OF EXPERIMENTAL ANIMALS IN RESPONSE TO ELEVATED PLASMA HOMOCYSTINE AND METHIONINE

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Abstract
The effects of high plasma concentrations of homocystine and methionine on the free amino acids of brain have been examined. Incorporation of the label from [35S]methionine into the free amino acid pools of rabbit brain was enhanced in response to high plasma homocystine or high plasma homocystine and mcthionine. Under comparable conditions a marked decrease in the incorporation of the label from [14C]glycine into the free pool was observed. The corresponding incorporation of 35S and 14C into brain proteins parallelled the results obtained with incorporation into the free pools of amino acids. Amino acid analyses of the free amino acid pools of rabbit brain revealed a general decrease in the concentration of amino acids in response to high plasma homocystine or high plasma homocystine and methionine. Inhibition of protein synthesis which occurs under the above experimental conditions is a general phenomenon. myelin and other brain fractions being equally affected. The decrease in concentration of brain amino acids also results in a diminution in concentration of the neurotransmitters GABA, dopamine and noradrenaline. The possible relationship of the observed changes to homocystinuria is discussed.