Ovarian influences on food intake and body weight regulation in lactating rats

In the following experiments, an attempt was made to determine the role of the ovary in the control of food intake and body weight regulation during lactation. In the first study, it was found that concentrations of estradiol benzoate effective in suppressing food intake and body weight in nonlactating animals were not effective during lactation. In the second experiment, ovariectomy during lactation was shown not to produce the usual increases in food intake and body weight or change in meal patterns known to occur after ovariectomy in the nonlactating rat. These results suggested that lactating animals behave the as though functionally ovariectomized and that the removal of the ovaries is of no additional consequence. The further observation that animals nursing small litters gained weight considerably more rapidly than animals nursing large litters led to the prediction that these animals would also be more responsive to the suppressive effects of EB. In the third study, EB in concentrations which are not effective in suppressing body weight in animals nursing large litters was found to suppress body weight in mothers with small litters. However, since these animals also showed a decline in milk yield, a number of alternative interpretations of these results were considered. These results, together with data concerning levels of ovarian hormones during gestation and lactation led to the hypothesis that pregnant and lactating animals undergo an elevation in body weight set-point, similar in magnitude and quality to elevations following ovariectomy in the nonlactating animal.