Vol. 274, Issue 6, E1040-E1049, June 1998
Effects of exercise on neuroendocrine secretions and glucose
regulation at different times of day
André J.
Scheen,
Orfeu M.
Buxton,
Maria
Jison,
Olivier
Van
Reeth,
Rachel
Leproult,
Mireille
L'Hermite-Balériaux, and
Eve
Van Cauter
Division of Diabetes, Nutrition and Metabolic Diseases, Department
of Medicine, University of Liège, B-4000 Liège; Center
for the Study of Biological Rhythms, Université Libre de
Bruxelles, B-1070 Brussels, Belgium; and Section of Endocrinology,
Department of Medicine, University of Chicago, Illinois 60637
To study the
effects of time of day on neuroendocrine and metabolic responses to
exercise, body temperature, plasma glucose, insulin secretion rates
(ISR), and plasma cortisol, growth hormone (GH) and thyrotropin (TSH)
were measured in young men, both at bed rest and during a 3-h exercise
period (40-60% maximal O2
uptake). Exercise was performed at three times of day characterized by marked differences in cortisol levels, i.e., early morning
(n = 5), afternoon
(n = 8), and around midnight
(n = 9). The subjects were kept awake
and fasted, but they received a constant glucose infusion to avoid
hypoglycemia. Exercise-induced elevations of temperature were higher in
the early morning than at other times of day. The exercise-induced
glucose decrease was ~50% greater around midnight, when cortisol was
minimal and not stimulated by exercise, than in the afternoon or early
morning (P < 0.05). This effect of
time of day appeared unrelated to decreases in ISR or increases in
temperature and GH. Robust TSH increases occurred in all exercise
periods and were maximal at night. The results demonstrate the
existence of circadian variations in neuroendocrine and metabolic
responses to exercise.
insulin secretion; cortisol; growth hormone; thyrotropin; circadian
rhythms
