Effect of Pitressin on old-age changes of salt and water metabolism in the rat

Abstract

Extracellular fluid volume is characteristically increased in old rats. This is accompanied by a parallel increase in extracellular Na but not K. Daily urine volume and, to a lesser degree, daily urinary Na excretion is also increased in old rats even in the presence of severe water deprivation. These changes, together with an increase in adrenal size, are similar to those observed in diabetes insipidus in the rat. Daily treatment with Pitressin tannate, tested at only one dose level, tended to restore the relevant values towards those of younger normals.