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Enzymatic and pharmacokinetic studies on the metabolism of branched chain α-keto acids in the rat

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Summary

Miehaelis-constants and enzyme activities for dehydrogenation and transamination of the three branched chainα-keto acids in liver, kidney, skeletal muscle, and brain of rats are reported.

After oral load only 11–22 % of the keto acids pass the liver unchanged.

Blood levels in pharmacokinetic and absorption studies are related to the Michaelis-constants. At the low keto-acid concentrations after oral application, dehydrogenation in the non-hepatic tissues is supposed to prevail over transamination. Data on feed efficiency of branched chain α-keto acids reported in the literature support this view. The chance for transamination is better after intravenous administration.

The transferability of our data to humans, and various factors influencing the efficiency of branched chain α-keto acids are discussed in connection with data reported in the literature.

Zusammenfassung

Michaelis-Konstanten und Aktivitäten von Dehydrogenasen und Transaminasen der drei verzweigten α-Ketosäuren Keto-Valin, Keto-Leucin und Keto-Isoleucin in Leber, Niere, Skeletmuskel und Gehirn von Ratten werden mitgeteilt.

Nach oraler Zufuhr passieren nur 11–22% der Ketosäuren unverändert die Leber.

Aus pharmakokinetischen und Resorptions-Untersuchungen erhaltene Blutspiegel an Ketosäuren werden zu den Michaelis-Konstanten in Beziehung gesetzt. Bei den geringen Konzentrationen an Ketosäuren nach oraler Zufuhr kann angenommen werden, daß die oxidativen Prozesse in den nichthepatischen Geweben über die Transaminierung überwiegen. Daten über die Wachstumseffizienz von verzweigtkettigen α-Ketosäuren im Vergleich zu den entsprechenden Aminosäuren stimmen mit dieser Vorstellung überein.

Bei intravenöser Verabreichung müßten die Voraussetzungen für Transaminierung besser sein als nach oraler Zufuhr. Auf der Basis von Daten aus der Literatur werden die Übertragbarkeit unserer Befunde auf den Menschen und die verschiedenen Faktoren, welche die Effizienz der verzweigten α-Ketosäuren durch Einwirkung auf ihren Stoffwechsel beeinflussen können, diskutiert.

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  1. K. H. Bässler

    Present address: Physiologisch-chemisches Institut der Universität Mainz, Deutschland

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  1. Physiologisch-chemisches Institut der Universität Mainz, Deutschland

    Astrid Pietrek

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Bässler, K.H., Pietrek, A. Enzymatic and pharmacokinetic studies on the metabolism of branched chain α-keto acids in the rat. Z Ernährungswiss 22, 14–26 (1983). https://doi.org/10.1007/BF02020781

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