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Accelerated rates of glycolysis in cardiac hypertrophy : are they a methodological artifact? Leong, Hon Sing


Glycolysis, measured by ³H₂0 production from [5-³H]-glucose, is accelerated in isolated working hypertrophied rat hearts. However, non-glycolytic detritiation of [5- ³H]- glucose by transaldolase in the non-oxidative pentose phosphate pathway (PPP) could lead to an overestimation of true glycolytic rates. Since the PPP may be upregulated in cardiac hypertrophy, I tested the hypothesis that detritiation of [5-³H]-glucose does not overestimate glycolysis in hypertrophied hearts and that accelerated rates of glycolysis reported in hypertrophied hearts are real and not artifactual. Glycolysis was measured by three independent methods in isolated working hearts from halothane-anesthetized shamoperated (Control) and aortic-constricted (Hypertrophy) rats. Two of the three methods determined glycolytic rates by quantifying the accumulation of glycolytic end products in timed collections of perfusate while the last method determined glycolytic rates by detritiation of [5-³H]]-glucose in the glycolytic pathway by production of 3H₂0. The first method involved enzymatic determination of lactate and pyruvate combined with rates of glucose oxidation. The second method involved determination of radiolabeled [¹⁴C]- lactate and [¹⁴C]-pyruvate accumulation combined with rates of glucose oxidation. The third method, which measures glycolytic flux by metabolism of [5-³H]-glucose, was in question and thus was used for comparison with the aforementioned alternative methods of determining glycolytic flux. Glycolysis was accelerated in hypertrophied hearts, regardless of the method used. There was also excellent concordance between the three methods with no significant differences in glycolysis detected between corresponding groups. Moreover, glucose-6-phosphate dehydrogenase activity and transaldolase expression, enzymes controlling key steps in the oxidative and non-oxidative PPP, respectively, were not different between control and hypertrophied hearts. Thus, nonglycotytic loss of 3H₂0 from [5-³H]-glucose is insignificant and 3H₂0 production from [5-³H]- glucose is an accurate means to measure glycolysis in isolated working normal and hypertrophied rat hearts. Furthermore, the PPP does not appear to be increased in this model of cardiac hypertrophy.

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