Response of rats with experimental diabetes insipidus to water and salt loading

¹ Veterans Administration Hospital and the Department of Medicine, University of Minnesota, Minneapolis, Minnesota

Water and salt loading experiments were carried out on normal male rats and rats with chronic diabetes insipidus (DI). The effect of two additional variables has been studied, i.e. that of withholding food and water prior to loading and that of the route of administration of the load (oral or intraperitoneal). Water deprivation prior to water loading reduced the excretion of water by DI animals far below that of normal rats regardless of the route of administration. Salt loading, on the contrary, obviated the influence of prior water deprivation and in every instance DI animals excreted more of the load as compared to controls. The quantitative but not qualitative excretion of both a water and saline load was affected when the intraperitoneal route was used. In both normal and DI rats potassium excretion far exceeded the output of sodium and chloride during water loading regardless of prior food and water deprivation. Desoxycorticosterone acetate (DCA) enhanced sodium excretion in saline loaded hydropenic normal rats but failed to influence sodium excretion in DI rats. Pitressin failed to produce an antidiuretic effect during saline diuresis; however, there was a marked increase in the excretion of salt and potassium in both DI and normal animals.