Effect of glucose-water ingestion on exercise thermoregulation in men dehydrated after water immersion.
BACKGROUND
The influence of non-ionic osmols on thermoregulation is unclear.


OBJECTIVE
Hyperglycemia will attenuate the rise in exercise core temperature.


METHODS
Dehydrated by 4-h of water immersion (34.5 degrees C) to the neck, 6 men, (35+/-SD 7 yr) participated in each of three trials where 2.0 g x kg(-1) body wt of oral glucose (33.8% weight per volume) was consumed followed by 80 min supine rest (Glu/Rest), or 70 min supine cycle exercise at 62.8%+/-SE 0.5% (1.97+/-0.02 L x min(-1)) peak O2 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, Hct, Na+, K+, Osm, and glucose; mean skin (Tsk) and rectal (Tre) temperatures, and sweating rate (resistance hygrometry) and skin blood velocity (laser Doppler) were measured intermittently.


RESULTS
Mean percent changes in plasma volume (p<0.05) for the exercise trials were not different: -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 (108.4+/-3.9 vs. 85.6+/-1.6 mg x dL(-1), respectively, p<0.05). Glu/Ex vs. No Glu/Ex data, respectively, at the end of exercise indicated that: Tre was lower by 0.4 degrees C (38.2+/-0.2 vs. 38.6+/-0.1 degrees C, p<0.05), Tsk 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 x cm(-2) x min(-1), p<0.05); and head (temporal) skin blood velocity was not different (1.67+/-0.21 vs. 1.51+/-0.24 Hz x 10(3), NS).


CONCLUSIONS
Elevation 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 could enhance body heat loss.
Dearborn
A S
AS
Laboratory for Human Environmental Physiology, NASA, Ames Research Center, Moffett Field, CA 94035-1000, USA.
Ertl
A C
AC
Jackson
C G
CG
Barnes
P R
PR
Breckler
J L
JL
Greenleaf
J E
JE
D000284:Administration, Oral; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D001831:Body Temperature / Q000187:drug effects* / Q000502:physiology*; D001833:Body Temperature Regulation / Q000187:drug effects* / Q000502:physiology*; D003681:Dehydration / Q000188:drug therapy* / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D015444:Exercise / Q000502:physiology*; D005947:Glucose / Q000627:therapeutic use*; D006801:Humans; D007101:Immersion / Q000009:adverse effects*; D008297:Male; D009994:Osmolar Concentration; D010101:Oxygen Consumption; D010953:Plasma Volume; D012146:Rest / Q000502:physiology; D016683:Supine Position; D014867:Water
D001786:Blood Glucose; D014867:Water; D005947:Glucose