title: Exercise-induced hyperthermia and hormonal responses to exercise.
abstract: Changes in plasma hormonal concentrations during exercise have been ascribed to the type, duration, and intensity of exercise, physical fitness of subjects, oxygen availability and debt, and acid-base balance. However, relatively few studies have examined the possible role of exercise-induced hyperthermia. This paper reviews previous studies on this subject and describes a series of experiments carried out in our laboratories to define the role of changes in body temperature in the release of hormones during exercise. In a first series of experiments, we studied the relationship between thermoregulatory and growth hormone responses to severe exercise at 23 degrees C for 2 h in fit euhydrated subjects, controlling the core temperature increase to a maximum of 40 degrees C by varying wind speed. Exponential relationships were found between increases in core temperature and plasma growth hormone, prolactin, and catecholamines during exercise, suggesting the existence of a thermal threshold for stimulation of hormonal release during exercise. The effect of endurance exercise with and without a thermal clamp (immersion in cold and warm water) on hormonal and leukocyte responses was examined. Again, a significant exponential relationship was found between increases in core temperature and hormonal responses. Thermal clamping significantly diminished the hormonal and the leukocytic responses to exercise, suggesting that an exercise-induced thermal threshold of approximately 38 degrees C exists where hormonal responses are observed. Therefore, core temperature increases may be integrated in the controlling system of hormonal and leukocytic responses to exercise.
authors.affiliation: Defence and Civil Institute of Environmental Medicine, North York, ON, Canada. manny.radomski@dciem.dnd.ca
authors.forename: M W
authors.initials: MW
authors.lastname: Radomski
authors.forename: M
authors.initials: M
authors.lastname: Cross
authors.forename: A
authors.initials: A
authors.lastname: Buguet
mesh_terms: D001831:Body Temperature; D001833:Body Temperature Regulation; D002395:Catecholamines / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005334:Fever / Q000209:etiology / Q000378:metabolism*; D013006:Growth Hormone / Q000378:metabolism; D006728:Hormones / Q000378:metabolism*; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D007962:Leukocytes / Q000502:physiology
chemical_list: D002395:Catecholamines; D006728:Hormones; D013006:Growth Hormone