Studies on estrogen receptors in rat uterus during protein malnutrition and steroid-maintained pregnancy

The present studies were performed to determine the nature and subcellular distribution of estrogen receptors (ER) in rat uterus, exposed to several cellular and hormonal responses as a result of dietary protein restriction. In protein-deficient rats, the concentration of estrogen receptors in uterine nuclei was lowered as compared to animals fed an 18% casein diet. No remarkable changes were observed in the cytosol estrogen receptor concentration in protein-deficient groups when values were expressed per milligram DNA. On day 15 of normal and steroid-maintained pregnancy, most of the receptor population was localized in the nuclear compartment with a significant decrease in cytosol receptor levels, as compared to virgin controls. However, on day 20 of steroid-maintained pregnancy, a marked reduction was recorded both in nuclear and cytosol estrogen receptors, as compared to that of day 15. Translocation study with protein-deficient rats revealed that the pattern of nuclear accumulation of estrogen receptors as a function of time was identical to 18% casein-fed group. However, the magnitude of translocated receptors was significantly higher at 2 hours after hormone treatment in protein-deficient animals. Additionally, the antagonistic, antiestrogenic effect of progesterone on estrogen receptor distribution was more pronounced in the protein-deficient group. The changes in estrogen receptor concentrations and their correlation with hormonal variations during protein malnutrition have been discussed.