Enhanced glucose availability for working muscles reduces exercise hyperthermia in dogs.

Body temperature and metabolic responses to 2 h treadmill exercise in dogs given glucose intravenously (25-30 mg.kg-1 X min-1 throughout the run) were compared with those measured in the same animals with elevated plasma FFA concentrations (soya bean oil ingestion + intravenous heparin) and in control experiments (24 h fasting). In comparison with control conditions enhanced glucose availability for the working muscles caused a reduction in the exercise-induced increases in both rectal (by 0.9 +/- 0.11 degree C) and muscle (by 0.9 +/- 0.16 degree C) temperatures, a lower rate of oxygen uptake (by 16%) and an elevated respiratory exchange ratio. A tendency towards enhanced body temperature responses to exercise, accompanied by increases in VO2 and cardiac frequency was noted in dogs with elevated plasma FFA concentrations as compared with the control animals. The estimated amount of heat effectively dissipated from the body, expressed as a fraction of heat load (thermoregulatory efficiency) was significantly higher in dogs infused with glucose (0.962 +/- 0.0035), than in the controls (0.947 +/- 0.0043) and those with elevated plasma FFA concentrations (0.931 +/- 0.0029). It is concluded that the increased contribution of carbohydrates to the energy yield during exercise results in a marked attenuation of hyperthermia, associated with a reduced metabolic rate and improved thermoregulatory efficiency.