[Relation between osmo- and volume-regulation in mammals with different renal capacities for osmotic concentration of...

The effect of increase in osmolarity of the blood on osmotic and volume controls has been investigated in Wistar rats, Brattleboro rats and big gerbil by means of i. v. administration of polyethyleneglycol-400 (PEG). PEG injections (0.17 ml/100 g) increased osmolarity of the blood by 3-4% in rodents of the species under study; concentrations of sodium, potassium and urea changed unequally. Significant differences were revealed when comparing the work of kidneys: the diuresis elevated by 55.7 times in Wistar rats and their renal sodium and urea excretions exceeded more than two-fold the level of that at the peak of the diuresis in big gerbil and Brattleboro rat. PEG excretion rate was significantly lower in latters than in Wistar rats. The data obtained suggest that the volume regulation is predominant under osmotic control in Brattleboro rat and in big gerbil.