The dipsogenic activity of prolactin in male and female rats.

1. Ovine prolactin injected intravenously in doses of 10.0, 5.0, 1.0, 0.1 and 0 mg/kg body wt. caused neither drinking nor a change in urine output in normal water replete male and female rats. 2. The water intake of male rats subjected to 48 hr water deprivation was substantially increased after injection of prolactin. 3. The water intake of male and female rats injected I.P. with a hyperoncotic solution of polyethylene glycol (20 M) was significantly increased after injection of prolactin. 4. Prolactin ws found to act synergistically with a subthreshold dose of angiotensin II amide to cause significant drinking and fluid retention. 5. The drinking responses of male and female rats injected I.V. with hypertonic saline were not modified by prolactin. 6. It is concluded that prolactin may act to increase the net water gain of animals suffering a deficit of the extracellular fluid space but is without effect on stimuli arising from deficits in the intracellular fluid space.