The role of mouth state in the termination of drinking behavior in humans.

Drinking behavior produces a reduction in the unpleasant dry-mouth sensations that accompany thirst. However, it is unclear whether or not the termination of drinking behavior is governed by a mechanism that meters this process. Twenty-two participants were tested in both a "dry mouth" and a control condition. In the dry-mouth condition, they exercised for 20 min. Participants then placed two cotton-wool rolls in each cheek, adjacent to the upper and the lower teeth with the mouth closed, and then drank water through a straw until they felt satiated. The control condition was identical except that participants placed only a single roll in each cheek, adjacent to the lower teeth. Pilot testing confirmed that using two rolls in each cheek reduced saliva volume in the main oral cavity more effectively than one roll. In both conditions, thirst increased after exercise. However, intake volumes, the number of drinking bouts, and the duration of the drinking episodes, were significantly greater in the dry-mouth condition (means; episode = 93.8 s, bouts = 7.0, volume = 428 mL) than in the control condition (means; episode = 69.3 s, bouts = 4.7, volume = 300 mL). These findings suggest that the termination of drinking behavior is governed by changes in mouth dryness. More specifically, saliva production increases during drinking, and this attenuates the need to continue drinking to relieve mouth dryness.