Estrogen modification of feeding behavior in the female rat: Influence of metabolic state

The effects of estrogen on feeding behavior and body weight regulation of adult ovariectomized rats were observed after 48 hr of food deprivation. The depletion of body nutrient stores caused by food deprivation resulted in an attenuation of the effects of estrogen treatment on food intake, eating time, meal size, meal duration and the number of meals. Nevertheless, estrogen treatment in fasted animals did shorten the interval between meals immediately after access to food was restored. Indices of the satiating effects of individual meals and the deprivation effects of intervals between meals were calculated for selected times. These indices also indicated an influence of estrogen even in the fasted condition. Estrogen diminished the satiety produced by the first meal after food access was restored, while the deprivation effects of the interval between the first and second meals were enhanced. During the dark period on the first day of refeeding, the satiating effects of food remained reduced in the fasted condition, and estrogen did not appear to further affect satiety compared to oil treatment, but estrogen did lower the deprivation effects of intermeal intervals compared to oil treatment. Estrogen treatment in non-fasted animals lowered both satiety and deprivation effects during the dark period. The varying influence of estrogen on the deprivation effects of intermeal intervals suggests that the influence of estrogen depends upon the long-term effects of an animal's metabolic state.