THE mammalian placenta can concentrate amino acids and release them into the foetal circulation, where they appear at levels higher than on the maternal side1. This mechanism provides a larger pool for foetal protein synthesis, but normal placental function can become a handicap in some situations. In the presence of an excess of amino acids the placenta exacerbates the maternal imbalance and produces a prolonged hyperaminoacidaemia in the foetus2. This in turn may affect the transplacental transport of other amino acids. Such can be the case in ‘material phenylketonuria (PKU)’, which often results in offspring with brain damage and mental retardation3. Using an animal model of ‘maternal PKU’ we have studied alterations in tissue levels and placental transport of L-tyrosine (Tyr), L-tryptophane (Trp) and certain foetal brain enzymes. We have found a reduced foetal tissue concentration of Trp and impaired foetal brain uptake of Tyr and Trp in the foetuses of hyper-phenylalaninaemic dams, as well as reduced brain pyruvate kinase activity.
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WAPNIR, R., MOAK, S. & LIFSHITZ, F. Decreased foetal amino acid uptake, brain pyruvate kinase and intrauterine damage in maternal PKU. Nature 265, 647–648 (1977). https://doi.org/10.1038/265647a0
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