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Related Experiment Videos

Mechanisms regulating adipose-tissue pyruvate dehydrogenase.

B R Martin, R M Denton, H T Pask

    The Biochemical Journal
    |September 1, 1972
    PubMed
    Summary

    Pyruvate dehydrogenase activity in rat fat cells is influenced by intracellular pyruvate levels and modulated by insulin through mechanisms independent of lipolysis inhibition or cyclic AMP reduction. Further research is needed to explore potential calcium mediation.

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    Area of Science:

    • Biochemistry
    • Cellular Metabolism
    • Endocrinology

    Background:

    • Pyruvate dehydrogenase (PDH) is a key enzyme regulating carbohydrate metabolism.
    • Insulin's effect on PDH activity in adipose tissue is not fully understood.
    • Previous studies suggest complex regulatory mechanisms involving substrate availability and cellular signaling.

    Purpose of the Study:

    • To investigate the regulation of pyruvate dehydrogenase activity in rat epididymal fat cells and fat pads.
    • To elucidate the role of intracellular metabolites, hormones, and ions in modulating PDH activity.
    • To determine if insulin's activation of PDH is linked to its antilipolytic effects or changes in cyclic AMP levels.

    Main Methods:

    • Isolated rat epididymal fat-cell mitochondria were used to study PDH activity in response to ATP, ADP, and pyruvate.

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  • Rat epididymal fat pads were incubated in vitro with various substrates (glucose, fructose, pyruvate) and effectors (insulin, ouabain, nicotinate, prostaglandin E1).
  • Measurements included pyruvate dehydrogenase activity, ATP content, and assessment of lipolysis and cyclic AMP levels.

    • Main Results:

    • In isolated mitochondria, PDH activity showed an inverse relationship with ATP content and was activated by pyruvate, suggesting inhibition of pyruvate dehydrogenase kinase by ADP and pyruvate.
    • Extramitochondrial Na+ and nicotinate also activated PDH in mitochondria, while ouabain and insulin did not.
    • In fat pads, insulin, glucose, fructose, and pyruvate activated PDH. Insulin's activation was independent of its antilipolytic effect and reduction of cyclic AMP.
    • Ouabain and Na+-rich medium activated PDH in fat pads, suggesting a role for ion transport or membrane potential.

    Conclusions:

    • Extracellular glucose, fructose, and pyruvate likely activate PDH by increasing intracellular pyruvate levels.
    • Insulin activates PDH through a mechanism distinct from its lipolytic inhibition or cyclic AMP reduction.
    • The involvement of Ca2+ in mediating the effects of insulin, ouabain, and K+-free medium on PDH activity is proposed.