Effect of potassium solution on rehydration in rats: comparison with sodium solution and water.

Thermally dehydrated rats were given isotonic KCl, NaCl solution, or tap water ad libitum for 17 h and the differences of the restoration rate in fluid and cation were compared between the groups to elucidate the effect of Na+ and K+ ions on the replacement of each body fluid compartment during rehydration. When rats were provided with NaCl solution, the gains of fluid and Na+ exceeded the amounts lost during the dehydration period, while in the isotonic KCl and tap water groups fluid gain was 70% of the fluid lost during the dehydration period. The recovery of extracellular fluid (ECF) volume was 178% of the loss in the NaCl group and 50% in the KCl group. The Na+ concentration of the ECF was regulated closely in all groups. The recovery in intracellular fluid (ICF) volume did not differ significantly between groups and never exceeded the control level, but tended to be higher in the KCl group than in the NaCl group. These results indicated that in the ECF the regulation of Na+ concentration preceded that of volume while in the ICF, volume regulation had priority. In addition, the effect of K+ supplementation on the recovery of ICF volume after thermal dehydration was shown to be modest, unlike the effect of Na+ on the recovery of ECF volume.