Ovarian hormones and meal patterns in rats: effects of progesterone and role of gastrointestinal transit

Three experiments determined: (1) whether progesterone treatment would reverse the effects of estradiol benzoate (EB) on meal patterns of ovariectomized (OVX) rats, and (2) whether changes in gastrointestinal transit were responsible for the EB-induced changes in meal patterns. Progesterone (5 mg/day) reversed the effects of EB by increasing meal size and decreasing meal frequency in OVX, EB-treated rats. Progesterone had no effect on these measures in OVX rats that were not given EB. In a comparison of the rate of gastrointestinal transit, the rate of gastrointestinal transit was found to be faster in OVX rats injected with EB daily for two weeks than in OVX, oil-treated controls as measured under anesthesia with infusion of ten ml of liquid diet. However, this alteration in gastrointestinal transit does not appear to be responsible for the decreased meal size of EB-treated, OVX-rats, because the gastrointestinal changes are not observed 34-38 hr after an EB injection, a time at which meal size is already affected.