Schedule-induced polydipsia suppresses pituitary-adrenal activity in rats.

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Abstract
The effects of schedule-induced polydipsia (SIP) on pituitary-adrenal activity, as indicated by plasma levels of corticosterone, were examined. Male (experiments 1 and 3) and female (experiment 2) rats were reduced to 80% of their free-feeding weight and given daily sessions on an intermittent-feeding schedule (fixed time [FT] of 60 s). Half of the subjects in each experiment had water available during experimental sessions, and the other half did not. Animals with water available in the experimental chamber exhibited SIP in all 3 experiments. In experiment 1, blood samples were collected following food consumption in the home cage, a session on FT 60 s, and a session with pellets available in a cup in the experimental chamber. In experiment 2, blood samples were taken prior to and following an FT 60-s session and following a session with pellets available in a cup in the chamber. In experiment 3, pre- and post-session samples were obtained as in experiment 2. Subsequently, the opportunity to drink during sessions was removed, and the effect on corticoids was examined. Schedule-induced drinking suppresses pituitary-adrenal activity. Corticoid suppression may become a conditioned response to drinking in the chamber and corticoids return to pre-session levels following removal of water from the chamber. SIP may serve an arousal-reducing role in intermittent-feeding situations.