Fluid electrolyte changes during prolonged restriction of motor activity in rat.

Water and electrolyte changes in urine and plasma of rats during prolonged restriction of motor activity (hypokinesia), have been studied, on 90 male Wistar rats (375 to 396 g) during a 15 day period of prehypokinesia and during a 90 day period of hypokinesia (HK). All rats were divided equally into two groups: rats placed under ordinary vivarium conditions served as vivarium control rats (VCR) and rats subjected to HK served as hypokinetic rats (HKR). The hypokinetic effect was carried out by keeping the HKR group in small individual cages that restricted all their movements in all directions without hindering food and water intake. During the 15 days of the prehypokinetic period and during the 90 days of the hypokinetic period, fluid consumed and eliminated in urine, food intake, body weight, plasma sodium and potassium concentration and excretion thereof in urine, plasma osmolality, total protein plasma concentration, whole blood haemoglobin and haematocrit concentration were measured. In the HKR group water and food intakes decreased significantly (p < 0.05) when compared with the VCR group, whilst diuresis, excretion of sodium and potassium in urine, plasma sodium and potassium concentration, plasma osmolality, plasma protein concentration, whole blood haemoglobin and haematocrit increased significantly (p < or = 0.05) when compared with the VCR group. It was concluded that prolonged exposure to HK induces significant changes in water balance and in both urinary and plasma sodium and potassium in rat.