Food intake and meal pattern in response to hyperosmotic-induced dehydration in obese and lean Zucker rats

Obese Zucker rats display neurochemical modifications in the brain characteristic of dehydration, but are nevertheless hyperphagic. This suggests that the obese animals can be resistant to dehydration-induced anorexia. The aim of this study was to test the hypothesis by comparing the effects of dehydration on food intake and feeding pattern between obese and lean Zucker rats.

Intracellular dehydration in obese (fa/fa) and lean (Fa/Fa) Zucker rats was induced by replacing drinking water with hyperosmotic sodium chloride solutions (1.8% and 2.7%, consecutively, 4 d each). Daily food intake, meal size, and meal number were measured using an automated computerized rat eater meter before, during, and after the dehydration.

After 8 d of hyperosmotic challenge, body weight decreased by 15% and 10% in lean and obese rats, respectively. Obese rats displayed higher food intake and meal size than lean rats before, during, and after the dehydration. Drinking 1.8% and 2.7% sodium chloride solutes decreased gradually food intake and meal size in both lean and obese rats; however, obese rats had a higher percentage of food intake than lean rats during the osmotic challenge. Higher ratios of food to water intake characterized obese rats and the percentage of such ratios in obese versus lean rats were increased during the 2.7% sodium chloride load. Meal number was not affected by dehydration in obese rats, but it was decreased in lean rats during the 2.7% sodium chloride load and remained low during refeeding after the dehydration, when the meal size was increased.

Dehydration-induced anorexia is present in both obese and lean Zucker rats; however, obese rats are more resistant to dehydration by preserving their meal size and food intake. These results support a role for feeding-associated dehydration in the pathogenesis of hyperphagia and obesity.