Water and electrolyte excretion in rats during prolonged restriction of motor activity and chronic hyperhydration

The objective of this investigation was to evaluate the effect of daily intakes of water and salt on water and electrolyte changes and body hydration status of rats during prolonged restriction of motor activity (hypokinesia). Ninety Wistar rats weighing 370 to 390 g were used to perform the studies: They were equally divided into three groups: 1. Unsupplemented vivarium control rats (UVCR); 2 Unsupplemented hypokinetic rats (UHKR) and 3. Supplemented hypokinetic rats (SHKR). For the simulation of the effect of hypokinesia (HK), the UHKR and SHKR groups were kept in small individual cages made of wood, which restricted their movements in all directions without hindering food and water intake. The SHKR received daily an additional amount of 5 ml water/100 g body weight and 3 g sodium chloride per 100 g body weights. During the prehypokinetic period of 15 days and during the hypokinetic period of 90 days plasma and urinary sodium and potassium, water intake and water loss, food intake, body weight, plasma osmolality, whole blood hemoglobin, hematocrit and plasma protein concentration were determined. In the UHKR group, plasma and urinary electrolytes, diuresis, plasma osmolality, whole blood hemoglobin, hematocrit and plasma protein concentration increased significantly while fluid and food intake and body weight decreased significantly when compared with the SHKR and UVCR groups. In the SHKR, plasma and urinary electrolytes, urine excretion, plasma osmolality, whole blood hemoglobin, hematocrit and plasma protein concentration decreased while food and water intake and body weight increased significantly when compared with the UHKR group. In the UVCR group, these same variables remained stable or changed very little when compared with the SHKR group throughout the experimental period. It was concluded that daily intakes of fluid and a salt supplement may be used to increase body hydration level and decrease fluid-electrolyte excretion and body weight losses during prolonged restriction of motor activity.