Effect Of Circadian Rhythm On Change In Fluid-regulation Hormones During Cycling Exercise

Introduction
It is recognized that circadian rhythm exerts great effect on the fluid-regulation hormones [1,2,3,4], but we do not know
whether the effect remains during exercise (Ex). The study investigated in circadian influence on change in plasma
volume during 1-H cycling Ex.

Methods
Sixteen health men (21±2yrs) conducted two 1-h exercise (1-wk apart) with heart rate raised to 140±bpm, respectively
at 5AM and 5PM. Before (B), during (D), and after (A) Ex, norepinephrine (NE, high performance liquid
chromatography), aldosterone (ALD), atrial natriuretic peptides (ANP), and vasopressin (V) (radioimmunoassay) were
assessed. Two-way ANOVA was applied to compare the response to exercise between AM and PM.

Results
ANP, Ald and V were significantly greater in AM than PM, whereas NE was significantly less in AM than PM (see
table). Ex resulted in increases (P<0.05) of all hormones. The circadian rhythm related difference in NE, Ald and V, but
ANP, persisted following A.

Discussion/ Conclusion
The effect of the circadian rhythms on the fluid-regulation hormone response to Ex was significant and persistent. A
greater ANP observed in AM was probably associated with the overnight cardiopulmonary loading, which could
explain the greater dehydration occurred during Ex in AM than PM.

Referrences
[1]. Armbruster, H., Vetter, W., Becherhoff, R., et al. 1975. Diurnal variations of plasma aldosterone in supine man:
relationship to plasma renin activity and plasma cortisol. Acta Endocrinol (Copenh). 80(1):95-103.
[2]. Hofman, M.A., and Swaab, D.F.. 1994. Alterrations in circadian rhythmicity of the vasopressin-producing neurons
of the human suprachiasmatic nucleus (SCN) with aging. Brain Res. 651:134-142.
[3]. Linsell, C.R., Lightman, S.L., Mullen, P. E., Brown, M.J., and Causon, R. C. 1985. Circadian rhythms of
epinephrine and norepinephrine in man. J Clin Endocrinol Metab. 60(6):1210-5.
[4]. Sothern, R.B., Vesely, D.L., Kauabrocki, E.L., et al. 1995. Blood pressure and atrial natriuretic peptides correlate
throughout the day. Am Heart J. 129:907-16

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