ADH Levels during Salt Depletion in Dogs*

Two groups of trained dogs were subjected to sodium chloride depletion and plasma ADH concentration, renin activity, plasma sodium, plasma osmolality, blood volume, hematocrit and body weight were measured. In one group of animals, sodium depletion was created by restricting intake to 5 mEq/24 h. Despite a statistically significant decrease in body weight and blood volume and a corresponding increase in plasma renin activity, plasma ADH concentration was not seen to change significantly from control values. Similar findings were seen in a second group of dogs which were given a diuretic in addition to dietary sodium restriction. In these animals the decrease in blood volume and rise in plasma renin activity were proportionately greater. Plasma ADH concentration was not observed to change significantly in this group of animals either. Both groups of animals developed significant hyponatremia during the experiment. It is concluded that in these dogs, the secretion of ADH was not suppressed and consequently hyponatremia developed. It is suggested that endogenous angiotensin was responsible for the continued secretion of ADH at control levels.