Exogenous glucose oxidation during exercise in endurance-trained and untrained subjects

Jeukendrup, A. E., M. Mensink, W. H. M. Saris, and A. J. M. Wagenmakers. Exogenous glucose oxidation during exercise in endurance-trained and untrained subjects. J. Appl. Physiol. 82(3): 835–840, 1997.—To investigate the effect of training status on the fuel mixture used during exercise with glucose ingestion, seven endurance-trained cyclists (Tr; maximum O2 uptake 67 ± 2.3 ml ⋅ kg−1 ⋅ min−1) and eight untrained subjects (UTr; 48 ± 2 ml ⋅ kg−1 ⋅ min−1) were studied during 120 min of exercise at ∼60% maximum O2 uptake. At the onset of exercise, 8 ml ⋅ kg−1 ⋅ min−1of an 8% naturally enriched [13C]glucose solution was ingested and 2 ml/kg every 15 min thereafter. Energy expenditure was higher in Tr subjects compared with UTr subjects (3,404 vs. 2,630 kJ; P < 0.01). During the second hour, fat oxidation was higher in Tr subjects (37 ± 2 g) compared with UTr subjects (23 ± 1 g), whereas carbohydrate oxidation was similar (116 ± 8 g in Tr subjects vs. 114 ± 4 g in UTr subjects). No differences were observed in exogenous glucose oxidation (50 ± 2 g in Tr subjects and 45 ± 3 g in UTr subjects, respectively). Peak exogenous glucose oxidation rates were similar in the two groups (0.95 ± 0.07 g/min in Tr subjects and 0.96 ± 0.03 g/min in UTr subjects). It is concluded that the higher energy expenditure in Tr subjects during exercise at the same relative exercise intensity is entirely met by a higher rate of fat oxidation without changes in the rates of exogenous and endogenous carbohydrates.

Changes in breath 13CO2/12CO2 during exercise of different intensities

The measurement of breath 13CO2/12CO2 is commonly used during exercise to evaluate the oxidation rate of exogenous carbohydrates enriched in 13C. The aim of this study was to investigate whether exercise itself affects the 13C/12C ratio in expired air CO2 in relation to exercise intensity. The relative abundance of 13C and 12C in expired air CO2 was determined by isotoperatio mass spectrometry and expressed as delta 13C (in %o) by using Craig's formula and calibrated standards. Five healthy young men exercised on a treadmill after an overnight fast during > or = 105 min on four occasions and in a randomized order. Work rates were performed at approximately 30, 45, 60, and 75% of their maximal O2 uptake (VO2max). Delta 13C in expired air CO2 and respiratory exchange ratio (RER) were determined every 15 or 30 min during exercise. At 30 and 45% VO2max, a slight and not statistically significant increase in delta 13C was observed at 30 min. In contrast, at 60 75% VO2max, the rise was statistically significant and averaged 0.83 and 0.99%o, respectively. Average delta 13C (between 0 and 105 min) progressively increased with the intensity of exercise. Individual values of delta 13C and RER were positively correlated (r = 0.653, P = 0.002) as were values of delta 13C and endogenous carbohydrates utilized (r = 0.752, P < 0.001). Factitious or "pseudooxidation" of a 13C-enriched exogenous glucose load (indeed noningested) was calculated from the changes in expired air delta 13C. Over the whole period of exercise it was not statistically significant at 30 and 40% VO2max. However, over the first 60 min of exercise, such pseudooxidation of exogenous glucose was significant at 30 and 45% VO2max. In conclusion, by modifying the mix of endogenous substrates oxidized, exercise at 60% VO2max and above significantly increases the 13C/12C ratio in expired air CO2. At these intensities, this could lead to overestimation of the oxidation of 13C-labeled substrates given orally. At lower intensities of exercise, such overestimation is much smaller an affects mainly the values recorded during the initial part of the exercise bout.

High Carbohydrate Content in Snap Bean Leaves Stimulates Chinese Rose Beetle Feeding

Chinese rose beetle (CRB) (Adoretus sinicus Burmeister) preferential feeding based on leaf carbohydrate content was determined using `Hawaiian Wonder' snap bean (Phaseohs vulgaris L.) plants exposed to 0% ,40%, or 80% shade for 2 days. Plants exposed to 0% shade before CRBs fed had 8.5% leaf area consumed compared with 2.8% and 3.6% for 40% and 80% shade, respectively. Leaves exposed to 0% shade had a higher carbohydrate content than leaves exposed to 40% and 80% shade. Darkening the apical and subtending leaf with aluminum foil for 1 day before CRBs fed shifted CRB feeding from heavy feeding on the apical leaf and light feeding on the subtending leaves to a reversed feeding pattern-light feeding on the apical leaf and heavy feeding on the subtending leaves. Three snap bean cultivars grown under similar environmental conditions were compared to `Hawaiian Wonder' using a unifoliate split-leaf technique. Cultivars with a high endogenous carbohydrate content in their leaves had a higher percentage of leaf area consumed by CRBs than cultivars with low endogenous carbohydrates. This report suggests that high endogenous carbohydrate content in leaves stimulates CRB feeding.

In vitro studies on the induction of sporogenous tissue on leaves of cinnamon fern. II. Some aspects of carbohydrate metabolism

Since previous studies indicated a requirement for high levels of exogenous sucrose for induction of sporogenous tissue on excised set III leaves of cinnamon fern, the initial part of this study was performed to determine which hexose moiety of sucrose would serve as the more active substrate for sporangial induction. Glucose was found to be preferentially used for sporophyll induction and resulted in more extensive development than was seen in those leaves grown on fructose. Endogenous carbohydrate levels were measured by gas–liquid chromatography. In decreasing order of quantity, freshly excised primordia contained xylans, sucrose, fructose, β-D-glucose, xylose, and α-D-glucose. In leaves cultured on medium with sucrose levels of 2, 4, 6, 8, and 10%, the highest levels of all endogenous carbohydrates studied were found in leaves grown on medium with 2% sucrose. The xylans accumulated in leaves grown on medium with all sucrose levels and the amounts present were generally above those of uncultured primordia. The xylans represented the highest quantities of the carbohydrates measured and appeared to be a major storage carbohydrate in both cultured and uncultured leaves. The concentrations of sucrose, on the other hand, generally declined and were, in all cases, below the amounts in uncultured primordia. Increasing levels of exogenous sucrose above 2% generally resulted in a decline in levels of the other internal carbohydrates after [Formula: see text] weeks of culture, but the respective quantities were generally above those of freshly excised primordia. Enzymatic analysis failed to reveal any starch in the leaves. It is suggested that although increasing sucrose levels resulted in an increase in the growth rate, it would appear that sucrose is important in sporangial induction because of some mechanism in addition to its effect on an increasing growth rate.