Evidence against a role for prolactin in osmoregulation in the rat: water balance studies.

Adult rats were subjected to hydration and dehydration experiments. Blood samples were obtained via indwelling jugular cannulae or after rapid decapitation. In the experiments attention was given to the avoidance of stress. Intravenous infusion with 5 ml distilled water in 50 minutes in males and lactating females did not affect the plasma prolactin (PRL) concentration, although it caused a significant drop in plasma osmolarity. Dehydration obtained by injecting furosemide, while resulting in a marked increase in plasma osmolarity, had no effect on the plasma PRL level in male rats. Thirst experiments for 2, 3 and 4 days, which likewise caused a rise in plasma osmotic value, had no significant influence on plasma PRL. It is concluded that PRL in the adult rat is not important in water retention or for the regulation of plasma osmolarity.