The interactions of fluid and food intake in the spontaneous feeding and drinking patterns of rats.

Food and fluid intake are to some extent interdependent. In order to investigate the effect of food intake on the amount of fluid ingested and the intervals between draughts and the effect of fluid intake on the amount of food ingested and the intervals between meals, the eating, drinking, and core temperature of 15 adult male rats were continuously monitored for 14 days. Bouts of feeding and drinking were identified by three different definitions and the contents of the stomach at the beginning and end of these bouts was estimated with a computer model. The core temperature, estimated prebout stomach contents of food and fluid, and the amount of solid or water ingested during each bout were then used as predictors of the amounts ingested in draughts or meals using both univariate and multiple regression techniques. The bout sizes, core temperature, and postbout estimated stomach contents of food and fluid were used as predictors of the duration of the postdraught or postmeal intervals. The amount eaten in meals was found to be facilitated by both the amount of fluid in the stomach and the amount drunk during the meal, whereas the postmeal interval was not affected by fluid intake. Two different types of draughts were identified; draughts that occurred after brief interdraught intervals and appeared to be responsive to factors associated with fluid balance, and draughts that occurred with interdraught intervals over 15 min and appeared to be primarily determined in size and timing by eating. The results are similar to those found in humans and suggest that food intake is modified by fluid intake, whereas, fluid intake is primarily determined by food intake.