Peripheral tissue metabolism of
branched-chain amino acids (BCAA) and branched-chain
keto acids (BCKA) in the postabsorptive state was evaluated in 8 patients with
chronic renal failure (CRF) and 7 controls by measuring the arterial-deep forearm venous differences for BCAA and BCKA. Arterial whole blood levels of BCAA and BCKA were also measured in an additional 7 patients and 11 controls. In CRF, total BCKA levels are reduced owing to a decrease in ketoisocaproic
acid (KICA) and ketoisovaleric
acid (KIVA) levels, parallel to changes in BCAA levels, whereas levels of ketomethylvaleric
acid (
KMVA) are not different from controls. Both in normal conditions and in patients, arterial levels of individual BCAA are directly correlated with arterial levels of the corresponding BCKA. However, in CRF, the ratios of
leucine to KICA and of
isoleucine to
KMVA are increased. A direct correlation between KICA and HCO3- levels is observed. In CRF, the release of
leucine and
valine as well as of KICA and
KMVA from peripheral tissues is reduced, whereas KIVA is neither released nor taken up by the forearm. The lack of KICA release from peripheral tissues likely accounts for its low circulating levels. The depressed peripheral release of
leucine associated with the lack of KICA release suggests an increased degradation of
leucine which proceeds beyond the transamination step.