Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption

Shirreffs, Susan M., and Ronald J Maughan. Restorationof fluid balance after exercise-induced dehydration: effects of alcoholconsumption. J. Appl. Physiol. 83(4):1152-1158, 1997.The effect of alcohol consumption on therestoration of fluid and electrolyte balance after exercise-induceddehydration [2.01 ± 0.10% (SD) of body mass] wasinvestigated. Drinks containing 0, 1, 2, and 4% alcohol were consumedover 60 min beginning 30 min after the end of exercise; a differentbeverage was consumed in each of four trials. The volume consumed(2,212 ± 153 ml) was equivalent to 150% of body mass loss. Peakurine flow rate occurred later (P = 0.024) with the 4% beverage. The total volume of urine produced overthe 6 h after rehydration, although not different between trials(P = 0.307), tended to increase as thequantity of alcohol ingested increased. The increase in blood(P = 0.013) and plasma(P = 0.050) volume with rehydrationwas slower when the 4% beverage was consumed and did not increase tovalues significantly greater than the dehydrated level(P = 0.013 andP = 0.050 for blood volume and plasmavolume, respectively); generally, the increase was an inverse functionof the quantity of alcohol consumed. These results suggest that alcoholhas a negligible diuretic effect when consumed in dilute solution aftera moderate level of hypohydration induced by exercise in the heat.There appears to be no difference in recovery from dehydration whetherthe rehydration beverage is alcohol free or contains up to 2% alcohol,but drinks containing 4% alcohol tend to delay the recovery process.

     

Fourier analysis of wing beat signals: assessing the effects of genetic alterations of flight muscle structure in Diptera.

A method for determining and analyzing the wing beat frequency in Diptera is presented. This method uses an optical tachometer to measure Diptera wing movement during flight. The resulting signal from the optical measurement is analyzed using a Fast Fourier Transform (FFT) technique, and the dominant frequency peak in the Fourier spectrum is selected as the wing beat frequency. Also described is a method for determining quantitatively the degree of variability of the wing beat frequency about the dominant frequency. This method is based on determination of a quantity called the Hindex, which is derived using data from the FFT analysis. Calculation of the H index allows computer-based selection of the most suitable segment of recorded data for determination of the representative wing beat frequency. Experimental data suggest that the H index can also prove useful in examining wing beat frequency variability in Diptera whose flight muscle structure has been genetically altered. Examples from Drosophila indirect flight muscle studies as well as examples of artificial data are presented to illustrate the method. This method fulfills a need for a standardized method for determining wing beat frequencies and examining wing beat frequency variability in insects whose flight muscles have been altered by protein engineering methods.     

Post-exercise rehydration in man: effects of electrolyte addition to ingested fluids

This study examined the effects on water balance of adding electrolytes to fluids ingested after exercise-induced dehydration. Eight healthy male volunteers were dehydrated by approximately 2% of body mass by intermittent cycle exercise. Over a 30-min period after exercise, subjects ingested one of the four test drinks of a volume equivalent to their body mass loss. Drink A was a 90 mmol·l^–1 glucose solution; drink B contained 60 mmol·l^–1 sodium chloride; drink C contained 25 mmol·l^–1 potassium chloride; drink D contained 90 mmol·l^–1 glucose, 60 mmol·l^–1 sodium chloride and 25 mmol·l^–1 potassium chloride. Treatment order was randomised. Blood and urine samples were obtained at intervals throughout the study; subjects remained fasted throughout. Plasma volume increased to the same extent after the rehydration period on all treatments. Serum electrolyte (Na⁺, K⁺ and Cl^–) concentrations fell initially after rehydration before returning to their pre-exercise levels. Cumulative urine output was greater after ingestion of drink A than after ingestion of any of the other drinks. On the morning following the trial, subjects were in greater net negative fluid balance [mean (SEM);P<0.02] on trial A [745 (130) ml] than on trials B [405 (51) ml], C [467 (87) ml] or D [407 (34) ml]. There were no differences at any time between the three electrolyte-containing solutions in urine output or net fluid balance. One hour after the end of the rehydration period, urine osmolality had fallen, with a significant treatment effect (P=0.016); urine osmolality was lowest after ingestion of drink A. On the morning after the test, subjects were in greater net negative sodium balance (P<0.001) after trials A and C than after trials B and D. Negative potassium balance was greater (P<0.001) after trials A and B than after C and D. Chloride balance was positive after drink D and a smaller negative balance (P<0.001) was observed after drink B than after A and C. These results suggest that although the measured blood parameters were similar for all trials, better whole body water and electrolyte balance resulted from the ingestion of electrolyte-containing drinks. There appeared, however, to be no additive effect of including both sodium and potassium under the conditions of this experiment.     

Gastric emptying, absorption, and carbohydrate oxidation during prolonged exercise.

This study was designed to examine aspects of digestive function that may limit assimilation of water and oxidation of orally ingested carbohydrate (CHO) during exercise. Eight males completed a crossover study in which each cycled on four occasions for 80 min at 70% maximal O2 consumption. Beverage was consumed at 0, 20, 40, and 60 min. Beverages were water, 4.5% glucose (4.5G), 17% glucose (17G), and 17% maltodextrin (17MD). CHO beverages contained 20 meq/l NaCl and were 13C enriched to measure exogenous CHO oxidation. Gastric (beverage) volume was measured at 80 min. Water uptake was estimated by including 2H2O in the beverage and measuring 2H accumulation in blood. Jejunal perfusion tests were conducted at rest with the same subjects and beverages. In 60 min, 1,294 +/- 31 (SE) ml were ingested; at 80 min, volumes emptied with H2O (1,257 +/- 32 ml) and 4.5G (1,223 +/- 32 ml) were greater than with 17G (781 +/- 56 ml) and 17MD (864 +/- 71 ml; P less than 0.05). Total CHO oxidized was similar with all beverages, but there was a greater increase in exogenous CHO oxidation over time with 17G and 17MD than with 4.5G; 54, 19, and 18% of the CHO ingested with 4.5G, 17G, and 17MD, respectively, was oxidized. This represents 57, 32, and 27%, respectively, of the CHO emptied from the stomach. 2H accumulation in the blood was more rapid with H2O and 4.5G than with 17G or 17MD. Net jejunal water absorption was greater from 4.5G than from water. Net water absorption was also observed from 17MD, whereas net secretion was observed with 17G.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fat and carbohydrate metabolism during low intensity exercise: effects of the availability of muscle glycogen

Four subjects were studied during exercise at 50% of maximum oxygen uptake after a normal diet, after a low carbohydrate (CHO) diet following exercise-induced glycogen depletion, and after a high CHO diet. This regime has previously been shown to cause changes in the amount of glycogen stored in the exercising muscles. Metabolic and respiratory parameters were measured during the exercise. The respiratory exchange ratio, blood lactate, blood pyruvate, blood glucose and plasma triglycerides were lower than normal following the low CHO diet and higher than normal following the high CHO diet. Plasma free fatty acids and plasma glycerol were higher than normal after the low CHO diet and lower than normal after the high CHO diet. The contribution of CHO to metabolism was less than normal after the low CHO diet and greater than normal after the high CHO diet. The altered availability of FFA does not appear to be a result of the variations in the blood lactate content.     

Diffusion Coefficients of Endogenous Cytosolic Proteins from Rabbit Skinned Muscle Fibers

Efflux time courses of endogenous cytosolic proteins were obtained from rabbit psoas muscle fibers skinned in oil and transferred to physiological salt solution. Proteins were separated by gel electrophoresis and compared to load-matched standards for quantitative analysis. A radial diffusion model incorporating the dissociation and dissipation of supramolecular complexes accounts for an initial lag and subsequent efflux of glycolytic and glycogenolytic enzymes. The model includes terms representing protein crowding, myofilament lattice hindrance, and binding to the cytomatrix. Optimization algorithms returned estimates of the apparent diffusion coefficients, D(r,t), that were very low at the onset of diffusion (∼10⁻¹⁰ cm² s⁻¹) but increased with time as cytosolic protein density, which was initially high, decreased. D(r,t) at later times ranged from 2.11 × 10⁻⁷ cm² s⁻¹ (parvalbumin) to 0.20 × 10⁻⁷ cm² s⁻¹ (phosphofructose kinase), values that are 3.6- to 12.3-fold lower than those predicted in bulk water. The low initial values are consistent with the presence of complexes in situ; the higher later values are consistent with molecular sieving and transient binding of dissociated proteins. Channeling of metabolic intermediates via enzyme complexes may enhance production of adenosine triphosphate at rates beyond that possible with randomly and/or sparsely distributed enzymes, thereby matching supply with demand.     

Quantitative trait loci of barley malting quality trait components in the Stellar/01Ab8219 mapping population

Malting barley is of high economic and scientific importance. Determining barley grains that are suitable for malting involves measuring malting quality, which is an expensive and complex process. In order to decrease the cost of phenotyping and accelerate the process of developing superior malting barley cultivars, markers for marker-assisted breeding are needed. In this study, we identified quantitative trait loci (QTLs) for malting traits in a Stellar/01Ab8219 F6:8 recombinant inbred line population grown at Aberdeen and Tetonia, Idaho, USA in 2009 and 2010. We identified QTLs associated with malt extract (ME), wort protein, soluble/total protein (S/T), diastatic power (DP), alpha-amylase, beta-glucan (BG) and free amino nitrogen (FAN) at a logarithm of odds score ≥2.5 using a high-density genetic map produced by merging Diversity Arrays Technology markers with the current single nucleotide polymorphism map. Novel QTLs were identified for DP and FAN on chromosome 5H, S/T on 6H, and BG and ME on 7H. Dissection of the genetic regions associated with malting traits suggests the involvement of multiple molecular pathways. The resulting molecular markers may prove useful for barley improvement.     

Cardiac Myosin Binding Protein-C Is Essential for Thick-Filament Stability and Flexural Rigidity

Using atomic force microscopy, we examined the contribution of cardiac myosin binding protein-C (cMyBP-C) to thick-filament length and flexural rigidity. Native thick filaments were isolated from the hearts of transgenic mice bearing a truncation mutation of cMyBP-C (t/t) that results in no detectable cMyBP-C and from age-matched wild-type controls (+/+). Atomic force microscopy images of these filaments were evaluated with an automated analysis algorithm that identified filament position and shape. The t/t thick-filament length (1.48 ± 0.02 μm) was significantly (P < 0.01) shorter than +/+ (1.56 ± 0.02 μm). This 5%-shorter thick-filament length in the t/t was reflected in 4% significantly shorter sarcomere lengths of relaxed isolated cardiomyocytes of the t/t (1.97 ± 0.01 μm) compared to +/+ (2.05 ± 0.01 μm). To determine if cMyBP-C contributes to the mechanical properties of thick filaments, we used statistical polymer chain mechanics to calculate a per-filament-specific persistence length, an index of flexural rigidity directly proportional to Young's modulus. Thick-filament-specific persistence length in the t/t (373 ± 62 μm) was significantly lower than in +/+ (639 ± 101 μm). Accordingly, Young's modulus of t/t thick filaments was ∼60% of +/+. These results provide what we consider a new understanding for the critical role of cMyBP-C in defining normal cardiac output by sustaining force and muscle stiffness.