TY - JOUR

T1 - Diminished epinephrine response to hypoglycemia despite enlarged adrenal medulla in trained rats

AU - Stallknecht, B

AU - Kjaer, M

AU - Mikines, K J

AU - Maroun, L

AU - Ploug, T

AU - Ohkuwa, T

AU - Vinten, J

AU - Galbo, H

N1 - Keywords: Adrenal Medulla; Animals; Blood Glucose; Epinephrine; Female; Hypoglycemia; Insulin; Norepinephrine; Physical Conditioning, Animal; Rats; Rats, Inbred Strains

PY - 1990

Y1 - 1990

N2 - Studies in humans have indicated that trained athletes compared with sedentary subjects have an increased capacity to secrete epinephrine. To investigate whether this is due to an adaptation induced by physical training or a selection phenomenon, rats were swim trained (T) 10 wk for 6 h/day or served as controls being either sedentary freely eating (C), food restricted (FR), sham swim trained (ST), or cold stressed (CS). Adrenal glands were weighted and cross sectioned for light microscopic determination of size of the adrenal medulla. Endurance-trained compared with control rats had heavier adrenal glands (P less than 0.05), higher catecholamine content in the glands (P less than 0.05), and higher adrenal medulla volumes (P less than 0.05) [males: 2.74 +/- 0.16 (T) vs. 2.05 +/- 0.16 (C), 1.90 +/- 0.10 (ST), and 2.21 +/- 0.08 mm3 (CS)] [females: 2.55 +/- 0.11 (T) vs. 1.92 +/- 0.06 mm3 (C)]. Cold stress or sham swim training did not increase adrenal weight or volume of adrenal medulla (P greater than 0.05). To stimulate adrenal medulla secretion, rats had an insulin-induced hypoglycemia. Insulin dose needed to suppress plasma glucose below 4.0 mM was four times greater in sedentary compared with trained rats. During hypoglycemia the epinephrine response was much smaller in trained than in untrained rats (P less than 0.05). In conclusion, in rats strenuous endurance training causes an enlargement of the adrenal medulla. However, possibly reflecting an adaptation within the central nervous system to reduced blood glucose levels induced by repeated exercise bouts, the epinephrine response to insulin-induced hypoglycemia is markedly diminished after training.

AB - Studies in humans have indicated that trained athletes compared with sedentary subjects have an increased capacity to secrete epinephrine. To investigate whether this is due to an adaptation induced by physical training or a selection phenomenon, rats were swim trained (T) 10 wk for 6 h/day or served as controls being either sedentary freely eating (C), food restricted (FR), sham swim trained (ST), or cold stressed (CS). Adrenal glands were weighted and cross sectioned for light microscopic determination of size of the adrenal medulla. Endurance-trained compared with control rats had heavier adrenal glands (P less than 0.05), higher catecholamine content in the glands (P less than 0.05), and higher adrenal medulla volumes (P less than 0.05) [males: 2.74 +/- 0.16 (T) vs. 2.05 +/- 0.16 (C), 1.90 +/- 0.10 (ST), and 2.21 +/- 0.08 mm3 (CS)] [females: 2.55 +/- 0.11 (T) vs. 1.92 +/- 0.06 mm3 (C)]. Cold stress or sham swim training did not increase adrenal weight or volume of adrenal medulla (P greater than 0.05). To stimulate adrenal medulla secretion, rats had an insulin-induced hypoglycemia. Insulin dose needed to suppress plasma glucose below 4.0 mM was four times greater in sedentary compared with trained rats. During hypoglycemia the epinephrine response was much smaller in trained than in untrained rats (P less than 0.05). In conclusion, in rats strenuous endurance training causes an enlargement of the adrenal medulla. However, possibly reflecting an adaptation within the central nervous system to reduced blood glucose levels induced by repeated exercise bouts, the epinephrine response to insulin-induced hypoglycemia is markedly diminished after training.

M3 - Journal article

C2 - 2240282

VL - 259

SP - R998-1003

JO - American Journal of Physiology - Cell Physiology

JF - American Journal of Physiology - Cell Physiology

SN - 0363-6143

IS - 5 Pt 2

ER -