Intraperitoneal preloads of water, but not isotonic saline, suppress schedule-induced polydipsia in rats.

In Experiment 1, 10 ml intraperitoneal preloads of water completely suppressed the acquisition of schedule-induced polydipsia in four of six rats. Preloads of 10 ml of isotonic saline retarded the acquisition of polydipsia slightly, but there were no significant differences in asymptotic levels of water intake between Saline Preload and Sham Preload groups. Experiments 2 and 3 demonstrated that established polydipsia was suppressed by about 10 ml when 10 ml water preloads were given; whereas, 10 ml saline preloads had no significant effect on established polydipsia. These results demonstrate that schedule-induced polydipsia is sensitive to internal states of water balance.