Embryonic loss and progesterone metabolism in rats fed a high energy diet

To elucidate the mechanism of the reduction of embryonic loss due to an increase of dietary protein level in rats fed a high energy diet, the relationship between embryonic loss and progesterone metabolism was investigated in rats fed high energy diets (digestible energy: about 5 kcal/g) differing mainly in casein and starch contents. The embryonic loss was minimum in rats fed a relatively high protein-low starch diet (30% protein-19% starch) and maximum in rats fed a very high protein-very low starch diet (39.9% protein-2.5% starch). On the basis of measuring urinary pregnanediol and in vivo conversion from progesterone to urinary pregnanediol and in vivo conversion from progesterone to urinary pregnanediol in each group, the production of progesterone in the body was shown to vary. In vitro studies showed that the mechanism responsible may involve inhibition of progesterone synthesis by the ovary in the presence of a very high protein-very low starch diet.