THE EFFECTS OF OVARIAN STEROIDS ON FOOD AND WATER INTAKE AND BODY WEIGHT IN THE FEMALE RAT

Abstract

The influence of ovarian steroids on food intake (FI), water intake (WI) and body weight (BWt) was measured under various conditions. Ovariectomy results in an increase in FI and BWt, which plateaued around one month after surgery. Daily injection of 1.5 μg oestradiol benzoate (OB) initiated at this time significantly reduced both FI and BWt. This effect of daily OB treatment on FI is only transitory since the FI returns to normal during OB treatment although the effect on BWt is maintained throughout and beyond OB treatment. Following ovariectomy, WI gradually falls, but is returned to normal by daily OB treatment. When oestrogen treatment is initiated at the time of ovariectomy, the increase in FI and BWt is prevented. In additional ovariectomized rats, 3 μg OB was injected every fifth day with either progesterone or oil administered on the intervening days. Although no influence of progesterone injection (either with OB or alone) was detected, the intermittent injection of OB induced cyclic suppression of FI, and the pattern of FI approached that of the intact cycling female. Adaptation to the intermittent injection of OB was not observed. Finally, OB treatment was found to decrease the increased FI seen during pseudopregnancy by a proportion similar to the effect of oestrogen in the long-term ovariectomized animal. These results suggest that oestrogen, but not progesterone, is the ovarian hormone active in the regulation of intake parameters and body weight in the female rat.