Effect of heat stress on glucose kinetics during exercise

Abstract

To identify the mechanism underlying the exaggerated hyperglycemia during exercise in the heat, six trained men were studied during 40 min of cycling exercise at a workload requiring 65% peak pulmonary oxygen uptake (VO2peak) on two occasions at least 1 wk apart. On one occasion, the ambient temperature was 20 degrees C [control (Con)], whereas on the other, it was 40 degrees C [high temperature (HT)]. Rates of glucose appearance and disappearance were measured by using a primed continuous infusion of [6,6-2H]glucose No differences in oxygen uptake during exercise were observed between trials. After 40 min of exercise, heart rate, rectal temperature, respiratory exchange ratio, and plasma lactate were all higher in HT compared with Con (P < 0.05). Plasma glucose levels were similar at rest (Con, 4.54 +/- 0.19 mmol/l; HT, 4.81 +/- 0.19 mmol/l) but increased to a greater extent during exercise in HT (6.96 +/- 0.16) compared with Con (5.45 +/- 0.18; P < 0.05). This was the result of a higher glucose rate of appearance in HT during the last 30 min of exercise. In contrast, the glucose rate of disappearance and metabolic clearance rate were not different at any time point during exercise. Plasma catecholamines were higher after 10 and 40 min of exercise in HT compared with Con (P < 0.05), whereas plasma glucagon, cortisol, and growth hormone were higher in HT after 40 min. These results indicate that the hyperglycemia observed during exercise in the heat is caused by an increase in liver glucose output without any change in whole body utilization.

Development of a Neural Network for Prediction of Glucose Concentration in Type 1 Diabetes Patients

“…There are a multitude of factors that influence subsequent glucose concentrations in diabetes patients, including, but not limited to, insulin dosage, carbohydrate and nutritional intake, lifestyle (e.g., sleep-wake cycles and sleep quality, and exercise), and emotional states (e.g., stress, depression, and contentment). [4][5][6][7][8][9][10][11][12][13][14] The effect of these various factors on subsequent glucose levels is not fully understood and may be patient specific or similar across all diabetes patients. In order to optimize control in diabetes patients, there needs to be some method for quantifying or predicting future occurrences of dysglycemia (i.e., high and low blood glucose concentration, also referred to as hyperglycemia and hypoglycemia, respectively).…”

Prior heat stress induces moderation of diabetic alterations in glycogen metabolism of rats

“…Previous investigations demonstrated that insulin concentrations gradually increase in lactating heat-stressed cows [33] and have confirmed this in growing heat-stressed calves [34,35] and pigs [36]. Also, decreased glucose level and increased insulin concentration was found in subjects adapted for 2 hours at 40°C [37].…”

Effect of Temperature on Muscle Metabolism During Submaximal Exercise in Humans

“…It is apparent from these results, therefore, that the augmented glycogen utilization in HL relative to CL was not secondary to changes in the adenine nucleotide pool or free inorganic phosphate (Pé) concentrations. An increased plasma adrenaline concentration has been observed during exercise and heat stress (Nielsen et al 1990;Febbraio et al 1994a;Hargreaves et al 1996a) which may partly account for the enhanced muscle glycogen utilization under such conditions (Febbraio et al 1998). However, since in the present study both legs were exposed to the same plasma adrenaline level and core temperature, this could not account for the observed difference in muscle glycogen utilization between HL and CL.…”