SALURETIC ACTION OF ALDOSTERONE IN THE PRESENCE OF INCREASED SALT INTAKE AND RESTORATION OF NORMAL ACTION BY PROLACTIN OR BY OXYTOCIN

SUMMARY The effects of aldosterone on sodium, potassium and water excretion during various treatment regimes were studied in six Merino ewes. Urine was collected from 12.00 to 14.00 h and from 14.00 to 16.00 h each day. Intravenous injections of either 1 ml isotonic saline or 500 μg aldosterone were given at 13.30 h and excretion during the second collection period compared with that in the first. When each animal was given a salt (NaCl) supplement of 80 mequiv./day by i.v. injection, aldosterone caused marked sodium retention with no effect on potassium. When salt supplements of 400 mequiv./day were given, aldosterone lost its sodium-retaining action in all animals and caused a marked saluresis with a small increase in potassium excretion in five sheep out of six. Injections of sheep pituitary prolactin or of oxytocin restored the sodium-retaining action of aldosterone in spite of a continued high salt intake. The animals gained very little weight when treated with 400 mequiv. salt alone but did gain significantly when treated with salt plus prolactin. The weight gain was rapidly lost when the prolactin and high salt intake were discontinued.