Partitioning of pyruvate between oxidation and anaplerosis in swine hearts

The goal of this study was to measure flux through pyruvate carboxylation and decarboxylation in the heart in vivo. These rates were measured in the anterior wall of normal anesthetized swine hearts by infusing [U-13C3]lactate and/or [U-13C3] pyruvate into the left anterior descending (LAD) coronary artery. After 1 h, the tissue was freeze-clamped and analyzed by gas chromatography-mass spectrometry for the mass isotopomer distribution of citrate and its oxaloacetate moiety. LAD blood pyruvate and lactate enrichments and concentrations were constant after 15 min of infusion. Under near-normal physiological concentrations of lactate and pyruvate, pyruvate carboxylation and decarboxylation accounted for 4.7 ± 0.3 and 41.5 ± 2.0% of citrate formation, respectively. Similar relative fluxes were found when arterial pyruvate was raised from 0.2 to 1.1 mM. Addition of 1 mM octanoate to 1 mM pyruvate inhibited pyruvate decarboxylation by 93% without affecting carboxylation. The absence of M1 and M2 pyruvate demonstrated net irreversible pyruvate carboxylation. Under our experimental conditions we found that pyruvate carboxylation in the in vivo heart accounts for at least 3–6% of the citric acid cycle flux despite considerable variation in the flux through pyruvate decarboxylation.

Pyruvate ingestion for 7 days does not improve aerobic performance in well-trained individuals

The purposes of the present studies were to test the hypotheses that lower dosages of oral pyruvate ingestion would increase blood pyruvate concentration and that the ingestion of a commonly recommended dosage of pyruvate (7 g) for 7 days would enhance performance during intense aerobic exercise in well-trained individuals. Nine recreationally active subjects (8 women, 1 man) consumed 7, 15, and 25 g of pyruvate and were monitored for a 4-h period to determine whether blood metabolites were altered. Pyruvate consumption failed to significantly elevate blood pyruvate, and it had no effect on indexes of carbohydrate (blood glucose, lactate) or lipid metabolism (blood glycerol, plasma free fatty acids). As a follow-up, we administered 7 g/day of either placebo or pyruvate, for a 1-wk period to seven, well-trained male cyclists (maximal oxygen consumption, 62.3 ± 3.0 ml · kg−1 · min−1) in a randomized, double-blind, crossover trial. Subjects cycled at 74–80% of their maximal oxygen consumption until exhaustion. There was no difference in performance times between the two trials (placebo, 91 ± 9 min; pyruvate, 88 ± 8 min). Measured blood parameters (insulin, peptide C, glucose, lactate, glycerol, free fatty acids) were also unaffected. Our results indicate that oral pyruvate supplementation does not increase blood pyruvate content and does not enhance performance during intense exercise in well-trained cyclists.

The determination of the availability to chicks of biotin in feed ingredients by a bioassay based on the response of blood pyruvate carboxylase (EC 6.4.1.1) activity

1. Experiments were carried out to establish the conditions required for the measurement of the availability to chicks of biotin in feed ingredients by a bioassay based on the response of blood pyruvate carboxylase (EC 6.4.1.1; PC) activity.2. Reference diets were formulated which gave a linear response in blood PC activity at 3 weeks of age over a wide range of supplemental dietary biotin concentrations.3. Dietary protein concentration was found to affect blood PC activity. Hence purified ingredients in the reference diets were wholly or partially replaced by the test ingredients so that all diets in each assay contained the same amounts of protein, fat and metabolizable energy. Comparison of the blood PC activities of birds$ given the test diets with those given biotin-supplemented reference diets provided a measure of the available biotin content of the test ingredient.4. Bioavailabilities of biotin were found to vary widely in the cereals and vegetable-protein sources tested.