Effect of glucose-water ingestion on exercise thermoregulation in men dehydrated after water immersion

Background: The influence of non-ionic osmols on thermoregulation is unclea r. Hypothesis: Hyperglycemia will attenuate the rise in exercise core tempe rature. Methods: Dehydrated by 4-h of water immersion (34.5 degrees C) to t he neck, 6 men, (35 +/- SD 7 yr) participated in each of three trials where 2.0 g.kg(-1) body wt of oral glucose (33.8% weight per volume) was consume d followed by 80 min supine rest (Glu/Rest), or 70 min supine cycle exercis e at 62.8% +/- SE 0.5% (1.97 +/- 0.02 L.min(-1)) peak O-2 uptake, followed by 10 min supine recovery with prior (Glu/Ex) or without glucose (No Glu/Ex ) ingestion. Blood samples were taken periodically for measurement of Hb, H ct, Na+, K+, Osm, and glucose; mean skin ((T) over bar sk) and rectal (Tre) temperatures, and sweating rate (resistance hygrometry) and skin blood vel ocity (laser Doppler) were measured intermittently. Results: Mean percent c hanges in plasma volume (p < 0.05) for the exercise trials were not differe nt: -12.3 +/- 2.2% (No Glu/Ex) and -12.1 +/- 2.1%(Glu/Ex). Mean (+/-SE) pre -exercise plasma [glucose] for Glu/Ex was higher than that of No Glu/Ex (10 8.4 +/- 3.9 vs. 85.6 +/- 1.6 mg.dL(-1), respectively, p < 0.05). Glu/Ex vs. No Glu/Ex data, respectively, at the end of exercise indicated that: Tre w a lower by 0.4 degrees C (38.2 +/- 0.2 vs. 38.6 +/- 0.1 degrees C, p < 0.05 ), (T) over bar sk was lower (32.0 +/- 0.3 vs. 32.4 +/- 0.2 degrees C, p < 0.05), forearm sweating rate was lower (0.94 +/- 0.09 vs. 1.05 +/- 0.07 mg. cm(-2).min(-1), p < 0.05); and head (temporal) skin blood velocity was not different (1.67 +/- 0.21 vs. 1.51 +/- 0.24 Hz.10(3), NS). Conclusions: Elev ation of plasma [glucose] prior to supine submaximal exercise in dehydrated men attenuates the increase of Tre without alteration of heat production, total body sweating, serum electrolytes and osmolality, or exercise-induced hypoglycemia: the mechanism may be enhanced peripheral blood flow that cou ld enhance body heat loss.