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

Abstract Background and objectives Obese Zucker rats display neurochemical modifications in the brain characteristic of dehydration, but are nevertheless hyperphagic. It suggests that the obese animals can be resistant to dehydration-induced anorexia. To test this hypothesis , we compared effects of dehydration on food intake and feeding pattern between obese and lean Zucker rats. Methods Intracellular dehydration in obese (fa/fa) and lean (Fa/Fa) Zucker rats was induced by replacing drinking water with hyperosmotic NaCl solutions (1.8% and 2.7%, consecutively, 4 days each). Daily food intake, meal size and meal number were measured using an automated computerized rat eater meter before, during and after the dehydration. Results After 8 days 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 vs. lean rats before, during and after the dehydration. Drinking 1.8% and 2.7% NaCl solutes decreased gradually food intake and meal size in both lean and obese rats, however, obese rats had higher percentage of food intake vs. lean rats during the osmotic challenge. Higher ratios of food to water intake characterized obese rats and the percentage of such ratios in obese vs. lean rats were increased during the 2.7% NaCl load. Meal number was not affected by dehydration in obese rats, but it was decreased in lean rats during the 2.7% NaCl load and remained low during refeeding after the dehydration, when the meal size was increased. Conclusion 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 of feeding-associated dehydration in the pathogenesis of hyperphagia and obesity.