Effect of hepatic portal infusion of water on water intake by water-deprived rats.

To determine whether or not hepatoportal osmoreceptive (or sodium-receptive) signals participate in the control of drinking, we examined the effects of portal infusion of water, 0.9% saline, and 1.8% saline on water intake by water-deprived rats. Infusion was started 0.5 h prior to the end of the water deprivation period for 3.5 h at a rate of 52 microliters/min through either a portal or a jugular catheter. After 24-h water deprivation, water intake was measured successively for 24 h without food. As a result of the water infusion tests, water intake of the portal infusion group was significantly less than that of the jugular infusion group during and after the infusion. Portal infusion of neither 0.9% nor 1.8% saline affected the water intake compared to similar infusion into the jugular vein. It is concluded that hypotonic stimulation of the hepatoportal osmoreceptor suppresses water intake in water-deprived rats. On the contrary, isotonic or hypertonic stimulation does not produce any change of water intake.