Hormonal responses during intense exercise preceded by glucose ingestion.

In this study the metabolic and endocrine responses during and after intense exercise (80% VO2max) were investigated under a) normal conditions b) diminished intra-muscular carbohydrate supplies, and c) an augmented supply of blood glucose. For this purpose four experimental conditions were employed, rest (R), rest with glucose ingestion (RG), exercise (E), and exercise with glucose ingestion (EG). On the exercise days the subjects exercised twice for 30 min with 2 hour rest between each bout. When glucose was ingested 15 min prior to exercise an accelerated glucose decrease occurred in the first 15 min of exercise (-35 mg/100 ml) (P less than 0.05). Insulin concentrations also decreased sharply throughout this exercise period (EG) (P less than 0.05). After exercise, an insulin rebound occurred in EG that was not observed after exercise in E. In EG, min (180-210) the exercise-induced GH increase was diminished (P less than 0.05) in comparison to the response observed during E. No differences were found in the cortisol responses during or after E and EG. (P greater than 0.05). It is concluded that moderate muscle and hepatic glycogen loss, induced several hours prior to exercise, does not alter the responses of cortisol, GH and insulin during exercise. Increasing the available glucose prior to exercise does not alter the cortisol or insulin responses during exercise but the diminished GH concentrations suggest that the release of this hormone is attenuated directly or indirectly by glucose and/or insulin.