Catecholamines and pancreatic hormones during autonomic blockade in exercising man

The effect of water temperature on the hormonal response to prolonged swimming

The relationship between thermoreception, hormonal secretion and muscular activity was studied. 6 men swam 60 min in 21, 27 and 33 degrees C water at a speed requiring 68% of VO2 max (determined in 27 degrees C water). Rectal temperature increased in 33 degrees C (1.3 +/- 0.2 degrees C, mean and S.E.) and 27 degrees C (0.7+/- 0.1 degrees C) expts. but decreased in 21 degrees C expts. (0.8 +/- 0.3 degrees C). Changes in esophageal and muscle temperatures parallelled changes in rectal temperature. Plasma noradrenaline was higher in 33 degrees C than in 27 degrees C expts. and growth hormone, cortisol and glucagon concentrations increased in 27 degrees C and 33 degrees C expts. only. Insulin concentrations were uniformly depressed during swimming at the different water temperatures. In 21 degrees C expts. noradrenaline and adrenaline concentrations were higher than in 27 degrees C expts. VO2, carbohydrate combustion and peak lactate were slightly lower in 33 degrees C expts. Plasma glucose decreased slightly and FFA and glycerol concentrations increased identically in all expts. Heart rate increased continuously during swimming in 27 degrees C and 33 degrees C expts., but not in 21 degrees C expts. In conclusion 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.

Effect of labetalol on plasma noradrenaline and adrenaline in hypertensive man

Injection i.v. of labetalol, a new adrenergic alpha- and beta-blocking agent, decreased arterial blood pressure in 9 hypertensive subjects resting in the supine position, when standing and during supine exercise. Heart rate after labetalol was unchanged in the resting supine position, and it fell in the latter two conditions. Plasma noradrenaline concentration was higher after labetalol in all three experiments as compared to a control study. Plasma adrenaline after labetalol was increased only in the standing position, when the highest plasma noradrenaline concentrations were observed. Blood glucose concentration tended to increase after labetalol, but the difference was not statistically significant. The changes in plasma noradrenaline and blood glucose after labetalol mimic findings observed after alpha-adrenergic receptor blockade. The beta-adrenergic receptor blocking property of labetalol is responsible for the reduced heart rate and it is likely to contribute to the higher plasma noradrenaline concentration observed when standing and during supine exercise.

Sympathetic control of metabolic and hormonal responses to exercise in rats

The importance of the sympatho-adrenal system for the pancreatic hormonal response to exercise and, furthermore, the role of glucagon and catecholamines for the hepatic glycogen depletion during exercise were studied. Rats were either surgically adrenomedullectomized and chemically sympathectomized with 6-hydroxydopamine or shamtreated. Two weeks later the rats had either rabbit-antiglucagon serum or normal rabbit serum injected. Subsequently the rats either rested or swam with a tail weight for 75 min. Immediately afterwards cardiac blood was drawn and liver and muscle tissue collected. In control rats in spite of an increase in blood glucose concentrati4ns during exercise plasma insulin concentrations were unchanged, while glucagon concentrations increased. In sympathectomized rats, compared to control rats, glucagon concentrations increased less, and insulin concentrations were higher, although glucose concentrations were lower during exercise. Sympathectomy completely abolished the exercise-induced decrease in liver and muscle glycogen concentrations, whereas neither glycogen depletion nor plasma catecholamine concentrations were influenced by the administration of glucagon antibodies. These findings indicate that the sympatho-adrenal system enhances glucagon secretion as well as muscular and hepatic glycogen depletion but inhibits insulin secretion in exercising rats. The increase in glucagon concentrations, however, does not enhance hepatic glycogen depletion at the work load used.