Blood glucose concentration dependent ACTH and cortisol responses to prolonged exercise

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Abstract
Responses of serum ACTH and cortisol concentration to low intensity prolonged exercise were investigated. In experiment 1, 10 subject fasted for 12 h and performed bicycle exercise at 49.3% .ovrhdot.VO2 max [maximal oxygen uptake] (.+-. 4.3%) until exhaustion or up to 3 h. During the early part of the exercise, serum ACTH and cortisol concentrations did not increase from the pre-exercise values (ACTH: 44 .+-. 5 .mu.g/l, cortisol: 139 .+-. 52 .mu.g/l). While the time to serum ACTH concentration increasing varied among the subjects (60-180 min), the increases of this hormone occurred for all subjects (175 .+-. 85 ng/l, P < 0.05) when blood glucose concentration decreased to a critical level of 3.3 mmol/l. At the end of the exercise, blood glucose concentration decreased to 2.60 .+-. 0.21 mmol/l, and serum ACTH and cortisol concentrations increased to 313 .+-. 159 ng/l and 371 .+-. 151 .mu.g/l, respectively. In experiment 2, 4 subjects performed the same intensity exercise until exhaustion, and were then give 600 ml of 20 g glucose solution, and immediately afterwards, were asked to repeat the same exercise. The subjects continued the exercise for between 30 to 90 min until again reaching exhaustion. During the 2nd exercise, blood glucose concentration increased to the pre-exercise value (2.72 .+-. 0.58 to 4.00 .+-. 0.22 mmol/l, P < 0.05) and simultaneously, serum ACTH concentration decreased considerably (354 .+-. 22 to 119 .+-. 54 ng/l, P < 0.05). Evidently, serum ACTH and cortisol concentration during low intensity prolonged exercise may be dependent on blood glucose concentration.