1. In rats the continuous I.V. infusion of ADH at rates up to 6·0 mu. kg−1 min−1 decreased drinking caused by water deprivation, by a 10% increase in osmotic pressure, and by caval ligation. 2. Infusion of ADH at rates between 0·07 and 6·0 mu. kg−1 min−1 never potentiated drinking nor did it significantly affect the 24 hr water intake of rats that were in water balance at the start of the experiment. 3. Urine output was slowed by a rate of infusion (13·0 μu. kg−1 min−1) which was approximately 150 times smaller than the lowest rate which was found to decrease water intake. 4. Since the rates of infusion of ADH which directly affect water intake and urine flow are so different, it is unlikely that ADH is a general homoeostatic hormone which controls both thirst and urine output in the rat.
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