Substrate signaling by insulin: a ketone bodies ratio mimics insulin action in heart.
Level 5 - mechanism / opinion, no new human data
Ex vivo animal laboratory study (isolated working rat hearts) with no human clinical data.
PubMed 9293956 · doi:10.1016/s0002-9149(97)00458-x
What was done
Researchers evaluated the metabolic and physiological effects of saturating doses of insulin, a physiological ratio of ketone bodies (4 mM D-beta-hydroxybutyrate and 1 mM acetoacetate), or both in an isolated, glucose-perfused working rat heart model. They measured glucose transporter 4 (GLUT4) activity, glycogen synthase activation, pyruvate dehydrogenase flux, oxygen consumption, hydraulic work, mitochondrial redox state, and cardiac efficiency.
What was found
Insulin administration increased GLUT4 membrane activity, stimulated glycogen synthesis, increased pyruvate dehydrogenase flux, reduced net glycolytic flux and oxygen consumption, doubled the cytosolic free phosphorylation potential ([sigmaATP]/[sigmaADP][sigmaPi]), and improved net cardiac efficiency by 28%. A 4:1 ratio of D-beta-hydroxybutyrate to acetoacetate qualitatively duplicated these metabolic effects and produced an equivalent improvement in cardiac efficiency. Combining both insulin and ketones in the perfusate increased the efficiency of cardiac hydraulic work by 35%.
Why it matters
The findings demonstrate that physiological ratios of ketone bodies can replicate insulin-mediated improvements in mitochondrial energetics and myocardial efficiency. This provides a biochemical rationale for investigating ketone bodies as metabolic therapeutics in insulin-resistant or failing hearts.
Limits
The study was conducted exclusively in an ex vivo rat heart perfusion model, which does not account for systemic neurohormonal regulation, chronic adaptations, or whole-body substrate availability. The abstract does not report the sample size (n), baseline variance, or statistical significance metrics. Findings cannot be directly extrapolated to human clinical outcomes without in vivo trials.
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- supports Langendorff perfused heart preparations show that the heart has greater hydraulic efficiency and generates proportionately more ATP per oxygen consumed in the presence of ketones.