SUMMARYWhen individual essential amino acids were omitted for periods of 40–100 min from the infusate substrate solution in isolated perfused guinea-pig mammary gland experiments, uptake of methionine, tyrosine, phenylalanine, histidine and tryptophan (group 1) was significantly depressed by a mean of 49·8%, whereas the remaining essential amino acids (group 2) showed no significant decrease in uptake. During depletion periods oxidation of [14C\amino acids was increased. The possible significance of the differences in absorption between the 2 groups of amino acids is discussed.
SUMMARYThe effects of high rates of infusion of essential amino acids on amino acid uptake by the isolated perfused guinea-pig mammary gland were studied. Infusion of methionine, tyrosine, phenylalanine, histidine and tryptophan (designated group 1) resulted in significant increases in the uptakes of tyrosine, phenylalanine and histidine. Methionine, tryptophan and other essential amino acids were not significantly affected. Infusion of threonine, valine, isoleucine, leucine, lysine and arginine (designated group 2) resulted in significant increases in uptake of all these amino acids. Group 1 amino acid uptake was not significantly affected. Infusion of all the essential amino acids (i.e. groups 1 and 2 together) resulted in significant increases in all their uptakes. Using as index ‘the predicted rate of protein synthesis’, infusion of group 1 and 2 together led to an apparent 27% increase in protein synthesis. The above results are discussed in relation to the control of milk protein synthesis by limiting essential amino acids.
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