水・電解質バランスにおよぼすサウナ浴後のスポーツ飲料摂取の影響

抄録

The purpose of the present study was to assess the effect of commercial sports beverage intake after a thermal exposure on water-electrolytes balance.
Nine healthy male volunteers with a mean age of 26.4 years, not heat acclimated, participated in a control experiment where no fluid was given (C experiment) . Five of them were given 500ml isotonic sports beverage containing Na⁺, K⁺, Cl^-and glucose (S. B experiment) and/or 500 ml tap water (Wa experiment) immediately after sauna exposure. The nude subjects were exposed to a sauna with 65 to 70°C (r. h. 50 to 60%) for 30 min.
Serum protein, electrolytes (Na⁺, K⁺, Cl^-), creatinine, plasma aldosterone (Ald), and catecholamines concentrations and excretions of electrolytes and aldosterone into urine were measured before, and 3, 30, 60, and 120 min after the sauna. Serum and urinary osmolalities, blood pressure, rectal temperature (Tr), heart rate, oxygen consumption and weight loss were also measured.
Body weight loss ranged from 50 to 750g. Serum protein, electrolytes and Ald concentrations increased significantly after the sauna. The enhanced levels of these variables and the depression of urine volume, urinary Na⁺excretion were maintained throughout the 2h recovery period in C experiment. Hydration associated with a reduced concentration of serum protein and electrolytes was observed at 30 min in S. B, at 60 min in Wa, and a dehydration occured again at 120 min both in S. B and Wa. A peak of urine volume was observed at 60 min in S. B and at 120 min in Wa during recovery. Free water clearance (C_H2O) was -0.98 ml/min/100 ml GFR (Ccr) prior to the exposure. With no fluid administration after the sauna, an excess in negative water balance remained throughout the 2 h recovery. But C_H2Ochanged from negative to positive at 60 and 120 min after sports beverage and/or water loadings.
A significant elevation of % TRNa (0.33 to 1.14%) was maintained after the sauna in both C and Wa experiment. Plasma Aid concentration and excretion of Aid in urine after the exposure were higher in both C and Wa than in S. B experiment. The increased Tr did not return to the initial level throughout the recovery. No significant differences were observed among the three experiments in heart rate and blood pressure as well as Tr.
The data indicate that salt deficit due to the sauna exposure was attenuated, but not prevented, by sports beverage intake, although the Aid secretion was alleviated. It is suggested that an over loading of sports beverage or water (i. e. 500 ml VS 50 to 750 g weight loss) leads to a marked and prompt water-diuresis, and to another dehydration. The increase of Tr as well as a partly salt deficit can be related to the rises in Ald secretion still observed at 2 h recovery.