Schedule-induced polydipsia: the role of oral and plasma factors.

To appreciate the contribution of oral and post-absorptive factors in the control of schedule-induced polydipsia (SIP), body fluid balance was determined at various times into the 4 hr session. Although dehydrated at the start of the session, rats quickly returned to normal balance which was maintained, despite excessive intake, by a brisk water diuresis. Plasma, as measured via the T-1824 technique, was also normal. Gastric infusion of water following each pellet delivery failed to eliminate the polydipsia despite marked hemodilution, whereas, oral infusion of equivalent amounts of water completely abolished the phenomenon. Taken together, these results suggest that SIP is mediated by oropharyngeal rather than hydration controls.