Influence of circadian rhythm changes of humoral regulation hormones on plasma volume during exercise

Aim: To investigate the effect of circadian rhythm changes of humoral regulation hormones on the plasma volume during exercise, and probe into the different influence on organ caused by exercise in the morning and afternoon. Methods: In November 2004, 16 healthy male undergraduates, who were studying in the Department of Rehabilitation, Shanghai Institute of Physical Education, participated in the exercise experiment of cycle ergometer twice at 5:00 in the morning and 17:00 after one week respectively, with the intensity that heart rate raised to 140 beats per minute for one hour, and then took a 1-hour rest. Plasma atrial natriuretic peptides (ANP), aldosterone (ALD) and arginine vasopressin (AVP) were determined before, during and after exercise respectively, besides, the changes of plasma volume, body mass, hemoglobin, haematocrit (Hct), ions of natrum (Na⁺) and kalium (K⁺) in blood and urine were also determined. Results: 1 Before exercise, plasma ANP, ALD and AVP were all higher in the morning than in the afternoon, which showed an obvious change with diurnal rhythm. Plasma ANP, ALD and AVP were all obviously increased during exercise, and this kind of change was still very significant. 2 Exercise both in the morning and afternoon had important influence on PV, it was manifested by the more decrease of PV and reduce of body mass in the morning [(6.1 ± 0.9)% and (1.03 ± 0.04) kg] than in the afternoon [(4.1 ± 0.6)% and (0.87 ± 0.02) kg] (P < 0.05), that was, exercise in the morning could lead to more deprivation of body fluids. 3 During exercise, the changes of hormones were highly correlated with PV and electrolyte changes, which indicated that the circadian rhythm changes of humoral regulation hormones played an important role in maintaining the balance of body fluid during exercise. Conclusion: 1 Humoral regulation hormones exhibit pronounced excretion with circadian rhythm, which is still obvious during exercise. 2 With the same intensity of exercise, deprivation of body fluids is greater in the morning than in the afternoon. 3 Circadian rhythm changes of humoral regulation hormones are still very obvious, which plays an important role in maintaining the balance of PV.