Organic acidurias : proceedings of the ninth symposium of the Society for the Study of Inborn Errors of Metabolism / edited by J. Stern and C. Toothill.

  • Society for the Study of Inborn Errors of Metabolism.
Date:
1972
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Organic acidurias : proceedings of the ninth symposium of the Society for the Study of Inborn Errors of Metabolism / edited by J. Stern and C. Toothill. Source: Wellcome Collection.

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    94 ORGANIC ACIDURIAS it was accompanied by greater excretion of the derivatives of the other branched-chain amino acids (Fig. 9). o,—0 o(-Ketoisocaproic Acid 0....0 o(-Ketoisovoleric Acid •—• c(-Keto-(3-methylvQleric Acid •7.9 KETO-ACID EXCRETION Mg/24 hours 0 Control Leucine Load I Control Valine Load I I Control Isoleucine Load Fig. 9. The increase in keto acid urinary excretion as a result of a load of each of the branched-chain amino acids (patient TA). This effect of leucine loading on the plasma levels of the other two branched-chain amino acids is different from the results obtained with the normal control subject. In the normal, a load of one of the branched- chain amino acids is followed by a fall in the levels of the other two branched-chain amino acids (Fig. 10). Again, the results after leucine loading are the most striking. Increased excretion of keto acid derivatives does not occur in the normal as a result of loading with the branched- chain amino acids. The mechanism of these plasma alterations in the normal has interested us for some time. They are not the result of interference with gastrointestinal absorption since they are manifest as soon as one hour after loading and while the subject is in the fasting state. They are not the result of alterations in renal tubular reabsorption; the urinary excretion of vahne and isoleucine is depressed after a load of leucine and an elevated excretion would be necessary to explain the fall in their plasma levels (Snyderman et al, 1968). The remaining hypothesis, that the depressed plasma levels of isoleucine and valine are the result of metabolic stimulation by excess leucine was confirmed by a study with rats (Phansalkar et al., 1970). Rats were given a dose of uniformly labelled isoleucine, and the expired was measured. After this rate of excretion had become constant, a load of leucine was adminis-