Glucocentric Metabolism in Ultra-Endurance Sled Dogs

Davis, Michael S.

doi:10.1093/icb/icab026

Cited by 7 publications

(6 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The typical conditioning program for ultraendurance sled dog racing has been shown to increase muscle oxidative capacity [ 27 , 28 ] without evidence of fiber type switching (based on myosin ATPase staining) [ 29 ]. Despite a diet that is strikingly high in fat [ 29 , 30 ], conditioning for endurance exercise in these athletes results in a distinct glucocentric metabolic strategy [ 31 ] characterized by high stimulus for hepatic glucose output during exercise [ 32 ] and increased capacity for peripheral glucose clearance [ 9 ]. Increased expression of glucose transporters provide a critical step in support of skeletal muscle utilization of glucose as the preferred substrate for exercise [ 28 , 33 ].…”

Section: Discussionmentioning

confidence: 99%

Conditioning-induced expression of novel glucose transporters in canine skeletal muscle homogenate

Barrett

Davis

2023

PLoS ONE

Self Cite

View full text Add to dashboard Cite

Athletic conditioning can increase the capacity for insulin-stimulated skeletal muscle glucose uptake through increased sarcolemmal expression of GLUT4 and potentially additional novel glucose transporters. We used a canine model that has previously demonstrated conditioning-induced increases in basal, insulin- and contraction-stimulated glucose uptake to identify whether expression of glucose transporters other than GLUT4 was upregulated by athletic conditioning. Skeletal muscle biopsies were obtained from 12 adult Alaskan Husky racing sled dogs before and after a full season of conditioning and racing, and homogenates from those biopsies were assayed for expression of GLUT1, GLUT3, GLUT4, GLUT6, GLUT8, and GLUT12 using western blots. Athletic conditioning resulted in a 1.31 ± 0.70 fold increase in GLUT1 (p <0.0001), 1.80 ± 1.99 fold increase in GLUT4 (p = 0.005), and 2.46 ± 2.39 fold increase in GLUT12 (p = 0.002). The increased expression of GLUT1 helps explain the previous findings of conditioning-induced increases in basal glucose clearance in this model, and the increase in GLUT12 provides an alternative mechanism for insulin- and contraction-mediated glucose uptake and likely contributes to the substantial conditioning-induced increases in insulin sensitivity in highly trained athletic dogs. Furthermore, these results suggest that athletic dogs can serve as a valuable resource for the study of alternative glucose transport mechanisms in higher mammals.

show abstract

Section: Discussionmentioning

confidence: 99%

Conditioning-induced expression of novel glucose transporters in canine skeletal muscle homogenate

Barrett

Davis

2023

PLoS ONE

Self Cite

View full text Add to dashboard Cite

show abstract

“…Even if our observation remains speculative, the kinetics of SCACs could reflect an increase in protein catabolism as SCACs increase in plasma is simultaneous to the decrease in serum globulins previously observed [ 11 ]. It has already been observed that dogs have a high gluconeogenic capacity from precursors as glycerol and lactate (the latter to a small extent) [ 12 , 68 , 69 ], and, probably more importantly, from amino acids [ 70 ]. Circulating amino acids derive either from dietary proteins or from endogenous protein catabolism.…”

Section: Discussionmentioning

confidence: 99%

“…Circulating amino acids derive either from dietary proteins or from endogenous protein catabolism. Commercial diets for sled dogs have a high protein content (>25–30%) [ 6 , 70 ]; the increase in serum urea nitrogen concentration observed in sled dogs during multiday exercise [ 11 ] sustains the idea that an important fraction of these proteins is used for gluconeogenesis [ 70 ]. Moreover, a decrease in serum globulin concentration [ 11 ], a loss of body mass and an increase in circulating cortisol have been reported in sled dogs during prolonged multiday exercise [ 1 , 11 ].…”

Section: Discussionmentioning

confidence: 99%

“…Further amino acid availability is induced by glucagon that increases amino acid extraction by the liver [ 71 ]. This extraction can be potentially high if proportional to serum glucagon rise observed in exercising sled dogs [ 70 ]. In humans, it has been suggested that despite the fact that protein contribution to energy expenditure is minor, exercise induces an increase in amino acids catabolism due to metabolic processes such as hepatic gluconeogenesis and TCA cycle.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Acylcarnitine profile in Alaskan sled dogs during submaximal multiday exercise points out metabolic flexibility and liver role in energy metabolism

et al. 2021

Self Cite

View full text Add to dashboard Cite

Alaskan sled dogs develop a particular metabolic strategy during multiday submaximal exercise, allowing them to switch from intra-muscular to extra-muscular energy substrates thus postponing fatigue. Specifically, a progressively increasing stimulus for hepatic glycogenolysis and gluconeogenesis provides glucose for both fueling exercise and replenishing the depleted muscle glycogen. Moreover, recent studies have shown that with continuation of exercise sled dogs increase their insulin-sensitivity and their capacity to transport and oxidize glucose and carbohydrates rather than oxidizing fatty acids. Carnitine and acylcarnitines (AC) play an essential role as metabolic regulators in both fat and glucose metabolism; they serve as biomarkers in different species in both physiologic and pathologic conditions. We assessed the effect of multiday exercise in conditioned sled dogs on plasma short (SC), medium (MC) and long (LC) chain AC by tandem mass spectrometry (MS/MS). Our results show chain-specific modification of AC profiles during the exercise challenge: LCACs maintained a steady increase throughout exercise, some SCACs increased during the last phase of exercise and acetylcarnitine (C2) initially increased before decreasing during the later phase of exercise. We speculated that SCACs kinetics could reflect an increased protein catabolism and C2 pattern could reflect its hepatic uptake for energy-generating purposes to sustain gluconeogenesis. LCACs may be exported by muscle to avoid their accumulation to preserve glucose oxidation and insulin-sensitivity or they could be distributed by liver as energy substrates. These findings, although representing a “snapshot” of blood as a crossing point between different organs, shed further light on sled dogs metabolism that is liver-centric and more carbohydrate-dependent than fat-dependent and during prolonged submaximal exercise.

show abstract

“…Athletic animals are those that have an overall greater level of physical fitness, measured by VO 2max values that are above average, indicating superior aerobic endurance (Poole et al, 2005). Sled dogs in particular have been noted to burnup to 11,250 kcal/day during long term bouts of exercise, (Davis, 2021, 2023; Hinchliff et al, 1997). As a result, the heat dissipation requirements are so great that, in human athletes, effective thermoregulation is the most pressing challenge during physical activity due to the large number of muscles contracting, and generating heat (El Helou et al, 2012; Lieberman & Bramble, 2007).…”

Section: Introductionmentioning

confidence: 99%

Thermal relations in sled dogs before and after exercise

Paul,

Jiménez

2024

J Exp Zool Pt A

View full text Add to dashboard Cite

Regulation of internal body temperature (Tb), or thermoregulation, is an evolutionarily conserved trait that places demand on basal metabolic rate of endothermic animals. Across species, athletes generate increased quantities of heat in comparison to their nonathletic counterparts and, therefore, must mediate physiological unbalance by upregulating the effectiveness of their heat dissipation abilities. Canine athletes are no exception to this phenomenon, however, with literature denoting body temperatures lower than nonathletic canines, it is clear they must possess adaptations to mitigate this demand. With VO2 max measurements of more than 200 mL/kg/min in sled dogs with mild training to 300 mL/kg/min in highly trained animals, sled dogs are a prime example of athleticism in canines. Seeking to determine correlations between Tear and body mass, morphology, and age of canine athletes, core body temperature (Tb) was measured with an instant ear thermometer, using Tear as a correlate before and after a 2‐mile run. In addition, we employed thermal imaging analysis to capture body‐wide heat dissipation patterns in sled dogs, and focused on thermal variation of mouth (Tmouth), nose (Tnose), and eyes (Teye). Furthermore, we looked at correlations between thermal variability across these four tissues and head morphology of each dog. Tear was consistently the highest temperature across all tissues measured, with a 1.5°C increase between pre‐ to postexercise (p < 0.001). Thermal imaging revealed significant positive correlations between Tmouth and body mass 15 min postexercise (p = 0.0023) as well as significantly negative correlations between Tnose and body mass at before exercise (p = 0.0468), Teye and nose length after run (p = 0.0076), and Tmouth and nose length after run (p = 0.0110). As body temperature rises during exercise, it becomes increasingly important to regulate blood flow throughout the body to supply working tissues with oxygen. This demand is offset by the role of the snout in evaporative cooling through panting, functioning as a prime location for heat dissipation and therefore maintaining significant relationships with many other vascularized tissues.

show abstract

Glucocentric Metabolism in Ultra-Endurance Sled Dogs

Cited by 7 publications

References 20 publications

Conditioning-induced expression of novel glucose transporters in canine skeletal muscle homogenate

Conditioning-induced expression of novel glucose transporters in canine skeletal muscle homogenate

Acylcarnitine profile in Alaskan sled dogs during submaximal multiday exercise points out metabolic flexibility and liver role in energy metabolism

Thermal relations in sled dogs before and after exercise

Contact Info

Product

Resources

About