The role of taste in rapid sodium satiation by sodium-deficient sheep

Sheep with a parotid fistula and sodium-deprived for 24 or 48 h (Na deficit = 500-700 mmol) were trained to drink their entire requirement of sodium bicarbonate solution from a cup in their cage in a single draught for up to 2 min. The cup was connected to a reservoir by an apparatus that enabled the concentration of the solution offered to be changed after the animal had drunk the first 100 or 150 ml of fluid without interrupting the flow of fluid or disturbing the drinking sheep. Under control conditions, the concentrations of solutions in the cup and reservoir were the same, either 900 mM or 300 mM NaHCO3. On experimental days, the concentration of NaHCO3 in the cup and reservoir were different so that the concentration of fluid increased from 300 mM to 900 mM or decreased from 900 mM to 300 mM NaHCO3. On those experimental days when the concentration of NaHCO3 was increased from 300 to 900 mM, the sheep drank a volume of fluid sufficient to maintain intake commensurate with loss. However, when the concentration of NaHCO3 was decreased from 900 to 300 mM, the sheep drank a volume of fluid insufficient to correct the deficit. It is proposed that the failure of sheep to react appropriately to a decrease in NaHCO3 concentration is a consequence of taste adaptation.