Estrogen Effects on Food and Fluid Intake by Ovariectomized Rats During Chronic Dehydration

Intracellular dehydration reduces food intake, and chronic dehydration is often used to study inhibitory signals that control eating. Estrogen influences both vasopressin secretion and water intake in response to dehydration, but it is unknown whether estrogen also influences food intake during dehydration. To determine whether estrogen affects inhibitory signals that control eating during dehydration, we used a protocol in which ovariectomized rats treated with estradiol benzoate (EB) or oil vehicle were given water or 2.5% NaCl for 4 days. On day 5, water was given to all rats. An automated system was used to monitor food and fluid intakes throughout the study. EB reduced feeding, and the inhibitory effect was most pronounced on day 4 of dehydration. However, there were no differences in the number of eating bouts, suggesting that, during dehydration, rats eat less per bout. Decreases in food intake were quickly reversed by rehydration, and EB‐treated rats ate amounts comparable to those by oil‐treated controls in the same number of bouts, indicating an increase in food intake/bout. EB treated rats drank less, but had more drinking bouts, regardless of hydration status. A decrease in fluid intake in an increased number of bouts suggests an increase in stimulatory signals to rehydrate that may be terminated by the effects of ingesting salt. As expected, both dehydrated groups increased water intake comparably during the first day of rehydration, regardless of EB treatment. Taken together, these results suggest that estrogen influences fluid intake during chronic dehydration, and that decreased feeding during dehydration is attributable to rapidly‐occurring inhibitory signals that are enhanced by EB treatment. Supported by OCAST HR12‐197