Inhibition of water intake by the central administration of IL-1beta in rats: role of the central opioid system.

In the present study we investigated, the effect of third ventricle injections of IL-1beta on water intake, in rats, induced by three different physiological stimuli: dehydration induced by water deprivation, hypernatremia associated with hyperosmolarity induced by intragastric salt load, and hypovolemia produced by subcutaneous polytethyleneglycol administration. Central administration of IL-1beta at the doses of 4 and 8 ng reduced water intake in all three conditions studied. Third ventricle injections of IL-1beta (8 ng) were unable to diminish water intake in the groups of rats pretreated with central injections of the non-selective opioid antagonist naloxone (10 microg) in the three different conditions studied. Furthermore, the central administration of IL-1beta was neither able to modify the intake of a 0.1% saccharin solution when the animals were submitted to a "dessert test" nor to induce any significant locomotor deficit in the open-field test. These results suggest that the central activation of interleukin-1 receptors by IL-1beta is able to impair the thirst-inducing mechanisms triggered by the physiological stimuli represented by dehydration, hyperosmolarity and hypovolemia. These results lead us to conclude that the antidipsogenic effects observed following central administration of IL-1beta require the functional integrity of the brain opiatergic system.