Effect of muscular exercise on adrenal 17-hydroxycorticosteroid secretion in the dog

Blood glucose concentration dependent ACTH and cortisol responses to prolonged exercise

The purpose of this study is to investigate responses of serum ACTH and cortisol concentration to low intensity prolonged exercise. In experiment 1, 10 subjects fasted for 12 h and performed bicycle exercise at 49.3% VO2max (+/- 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 micrograms/l, cortisol: 139 +/- 52 micrograms/l). Whilst 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 less than 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 micrograms/l, respectively. In experiment 2, four subjects performed the same intensity exercise until exhaustion, and were then given 600 ml of 20 g glucose solution, and immediately afterwards, they were asked to repeat the same exercise. The subjects continued the exercise for between 30 to 90 min until again reaching exhaustion. During the second exercise, blood glucose concentration increased to the pre-exercise value (2.72 +/- 0.58 to 4.00 +/- 0.22 mmol/l, P less than 0.05) and simultaneously, serum ACTH concentration decreased considerably (354 +/- 22 to 119 +/- 54 ng/l, P less than 0.05). The results of the present study suggest that serum ACTH and cortisol concentration during low intensity prolonged exercise may be dependent on blood glucose concentration.

Habituation of the corticosterone response of ducks (Anas platyrhynchos) to daily treadmill exercise

The habituation of the corticosterone response of ducks to treadmill exercise (1.1 km/hr 0 degrees incline for 60 min) has been determined over a 28-day period. In untrained birds 30 min of treadmill exercise resulted in a marked (P less than 0.001) increase in the basal plasma corticosterone level. After 60 min of exercise the corticosterone concentration remained elevated (P less than 0.001) in comparison with basal and control (nonexercised) levels but was less (P less than 0.01) than that at 30 min. Following exercise the concentration declined to basal levels within 60 min. After 7 days of daily training the peak (30 min) corticosterone response to exercise diminished by greater than 50% and was absent in birds trained for 21 days. This habituation of the corticosterone response may be due to adrenocortical stimulation by pituitary adrenocorticotrophin (ACTH) being reduced. As the stimulatory effect of ACTH administration (8 IU/kg) on corticosterone secretion does not habituate in birds treated daily (for 28 days), the reduced corticosterone response to exercise may be due to decreased ACTH release rather than to a reduction in adrenal ACTH sensitivity.

Effects of thyroxine and exercise on the glandular and plasma levels of corticosterone in the male rat

The results presented here demonstrates that the thyroid gland is essential for normal corticosterone production. They further show that exercise stimulates this production whether the thyroid gland is present or not. The release or metabolism of corticosterone seems dependent upon an intact thyroid gland since plasma levels of corticosterone are decreased during exercise if the thyroid is absent. The administration of thyroxine is not sufficient to renew these levels.

Variability of corticosteroid responses during exercise stress in active and sedentary middle-aged males

Two groups of middle-aged male subjects (both N=11), one active (mean age 44.6 years) and one sedentary (mean age 43.7 years), undertook a graded exercise stress test on a bicycle ergometer in the post-absorptive state. Blood serum corticosteroid levels were measured at the following stages of metabolism; at rest, under conditions of submaximal and "maximal' exercise and during recovery. The active group showed no significant change in mean serum corticosteroid levels from resting values, during exercise and recovery. However the sedentary group displayed a significant increase in mean serum corticosteroid levels from a resting value of 5.81 plus or minus 0.41 mub-g/100 ml. (mean plus or minus S.E.) to 7.83 plus or minus 0.71 mug/100 ml. during "maximal' exercise (p smaller than 0.05), which was maintained throughout recovery 7.82 plus or minus 0.70 ug/100 ml (p smaller than 0.05). Futhermore the active group demonstrated significantly lower mean serum corticosteroid levels compared with the sedentary group under conditions of submaximal (p smaller than 0.05) and "maximal' (p smaller than 0.01) exercise and during recovery (p smaller than 0.01). It was concluded that the variability in the response patterns of serum corticosteroids during exercise stress in active and sedentary middle-aged males, reflected the physiological differences observed between the two groups of subjects.

Glicocorticóides em afecções do sistema nervoso. Mecanismo de ação

Avaliação dos conhecimentos sobre 0s possíveis mecanismos da atuação glicocorticóide em afecções do sistema nervoso. Os dados sobre os hormônios glicocorticóides, a corticotrofina e o fator liberador da corticotrofina são revistes, bem como aqueles sobre a interação respectiva e o papel desempenhado por estruturas do sistema nervoso. As funções metabólicas dos glicocorticóides são revistas nos aspectos de maior interesse para o tema, após o que é discutida a atuação glicocorticóide em diversos grupos de afecções do sistema nervoso.