Individual effects of estradiol and progesterone on food intake and body weight in ovariectomized binge rats

Abstract

The individual roles of estradiol (E) and progesterone (P) in the control of food intake and body weight in ovariectomized (OVX) rats were investigated. Six groups of OVX Sprague-Dawley rats (n=9/group) were assigned to one of three 4-day cyclic hormone treatments: two groups were treated with E benzoate; two groups were treated with P; two groups were treated with both (EP). All rats had continuous access to chow and water throughout this 4-week study. One group of rats within each hormone treatment condition was fed chow ad libitum, and the second was subjected to a binge schedule: chow ad libitum plus 1-h access to an optional fat source on Monday, Wednesday, and Friday. A seventh OVX group (n=8) received the oil vehicle and chow. This group was included to monitor body weight and to verify hormone efficacy. The main findings were: (1) relative to rats receiving only P, E alone or EP attenuated 24-h chow intake tonically and cyclically, i.e. intake on Day 4, which models estrus, was lower in E and EP than in P, and also was lower than intake on Day 2, which models diestrus. In contrast, (2) neither E nor EP detectably affected optional fat intake during the 1-h fat access period relative to rats receiving only P when data were collapsed across the entire study. However, (3) E and EP had large effects on fat intake relative to P during the 1-h fat access period at the start of the study, but not at the end, when bingeing was fully established. (4) E and EP led to lower and apparently normal levels of body weight compared to rats receiving only the oil vehicle or only P. These results indicate that (1) administration of E alone has similar effects as co-administration of E and P on feeding and body weight in rats bingeing on fat, (2) with or without P, the inhibitory effects of E on meal size are compromised when bingeing on fat, and (3) the effects of E on binge size change dynamically as bingeing develops.

Figure 1

Effect of cyclic hormone treatment and fat access schedule on 1-h fat (shortening) (top), chow (middle) and total (bottom) energy intake. D=Day, E=Estradiol, P=Progesterone, EP=Estradiol/Progesterone. Small letters indicate tonic effects of estradiol in the binge groups; different letters indicate significant differences among the groups. There was no effect of cycle day on intake. # indicates significant differences between binge and chow groups within any given hormone treatment. For clarity only Day 4 comparisons are shown.

Figure 2

Effect of hormone treatment on 1-h fat intake on the first and last Day 4 of the study. D=Day, E=Estradiol, P=Progesterone, EP=Estradiol/Progesterone. One-h intake differed among the groups at the start of the study, but not at the end of the study. Different small letters indicate significant differences among the groups. Asterisk indicates a significant difference between intakes on Day 4 (start) and Day 4 (end) in the EPH group.

Figure 3

Effect of cyclic hormone treatment on daily energy intake. Top: 24-h total intake, i.e. 24-h total energy intake on days that binge rats did not have access to the optional fat. Middle: 24-h chow intake on days that binge rats did have access to the optional fat. Bottom: 24-h total energy intake (1-h fat plus chow) on days that binge rats had access to the optional fat. Note that 1-h fat intake is shown in Fig 1. D=Day, E=Estradiol, P=Progesterone, EP=Estradiol/Progesterone. Small letters indicate tonic effects of estradiol in the binge groups; different letters indicate significant differences among the groups. Numbers indicate tonic effects of estradiol in the chow groups; different numbers indicate significant differences among the groups. * indicates cyclic effect of estradiol in each group, i.e. intake on Day 4 significantly less than intake on Day 2. # indicates significant difference between binge and chow group within each hormone treatment. For clarity only Day 4 comparisons are shown.

Figure 4

Body weight at day 5 postovariectomy and weekly across this 4-week study. D=Day, W=Week. * indicates significant difference at the end of the study (W4) between the groups treated with estradiol and the groups treated with P or oil vehicle, i.e. PH=PC=OC > EH=EC=EPH=EPC.