Ovarian hormones inhibit fat intake under binge-type conditions in ovariectomized rats

Abstract

Binge eating is more common in females than in males. This study investigated the effects of ovarian hormones on binge-eating behavior in a diet-related rat model. Six groups of ovariectomized Sprague-Dawley rats were used (n=13/group). All rats had continuous access to chow and water throughout the study. One half of the rats were injected every fourth day with estradiol benzoate (2 microg/100 microl sesame oil) and progesterone (500 microg/100 microl sesame oil); the other half received only the sesame oil vehicle. Three feeding protocols were tested in each hormone injection condition: (1) chow only: no additional dietary fat access; (2) low-restriction: 1-h fat access every day; (3) high-restriction: 1-h fat access on Monday, Wednesday, and Friday. As previously reported in intact male and female rats, the high-restriction groups exhibited binge-like increases in 1-h energy intake during fat access. The major new finding of this study is that 1-h energy intake was tonically, but not cyclically, reduced in the hormone-treated high-restriction (binge) rats. Specifically, both low- and high-restriction hormone-treated rats consumed significantly less energy than did the oil-treated rats during the 1-h fat period (p<0.0001) and overall (p<0.0001), indicating a tonic inhibition of eating. However, food intake during the 1-h fat access period was also cyclically reduced in the hormone-treated low-restriction rats, but not in the hormone-treated high-restriction rats. These results indicate that the normal cyclic inhibitory influence of ovarian hormones on eating, but not their normal tonic inhibitory influence, is disrupted by conditions leading to binge-type eating.

Fig 1

Effect of cyclic hormone treatment and fat access schedule on 1-h energy intake. D=Day. # indicates significant differences among the C, L, and H groups within the OIL and EP rats (P<0.0001). * indicates significant differences between OIL and EP groups on the H and L feeding schedules (P<0.0001). † indicates intake on day 4 significantly different from intake on day 2 in EP-L group (P<0.05).

Fig 2

Effect of cyclic hormone treatment and fat access schedule on 24-h energy intake on binge days (Mon, Weds, Fri) and non-binge days (Tues, Thurs, Sat, Sun). D=Day. # indicates H rats ate significantly more than C and L rats on binge days (P<0.0001) and significantly less on non-binge days (P<0.0001). * indicates significant differences between OIL and EP groups on the C, L and H feeding schedules on binge days, and in C and L groups on non-binge days (P<0.0001). † indicates intake on day 4 significantly different from intake on day 2 within the EP-C, EP-L and EP-H groups (P<0.05).

Fig 3

Body weight at day 5 of postovariectomy and weekly across the 6-week study. # indicates final body weight of L and H rats greater than C rats in EP groups (P<0.05). * indicates significant difference between OIL and EP groups that had the same feeding schedule (P<0.001).