EFFECT OF WATER TEMPERATURE ON THE HORMONAL RESPONSE TO PROLONGED SWIMMING

The relationship between thermoreception, hormonal secretion and muscular activity was studied. Men [6] swam 60 min in 21, 27 and 33.degree. C water at a speed requiring 68% of .ovrhdot.VO2 max [maximum O2 consumption] (determined in 27.degree. C water). Rectal temperature increased in 33.degree. C (1.3 .+-. 0.2.degree. C, mean and SE) and 27.degree. C (0.7 .+-. 0.1.degree. C) expts [experiments], but decreased in 21.degree. C expts. (0.8 .+-. 0.3.degree. C). Changes in esophageal and muscle temperatures parallelled changes in rectal temperature. Plasma noradrenaline [norepinephrine] was higher in 33.degree. C than in 27.degree. C expts. and growth hormone, cortisol and glucagon concentrations increased in 27.degree. C 33.degree. C expts. only. Insulin concentrations were uniformly depressed during swimming at the different water temperatures. In 21.degree. C expts. noradrenaline and adrenaline [epinephrine] concentrations were higher than in 27.degree. C expts. .ovrhdot.VO2 carbohydrate combustion and peak lactate were slightly lower in 33.degree. C expts. Plasma glucose decreased slightly and FFA [free fatty acid] and glycerol concentrations increased identically in all expts. Heart rate increased continuously during swimming in 27.degree. C and 33.degree. C expts., but not in 21.degree. C expts. The rise in body temperatures normally observed during exercise enhances the exercise-induced increases in the plasma concentrations of noradrenaline, cortisol, growth hormone and glucagon. Decreased body temperatures may elicit catecholamine secretion as a direct consequence of thermoreception. Shivering may account for previously observed decreases in insulin secretion during cold stress but not for increases in cortisol and growth hormone.