Induction of cytosolic receptors for 1α,25-dihydroxyvitamin D₃ in the immature rat uterus by oestradiol

The role of oestradiol-17β in the induction of specific cytosolic receptors for 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) was examined in the immature rat uterus. An acrylamide gel electrophoretic analysis was developed to separate the specific receptor for 1,25(OH)₂D₃ from the plasma binding protein for vitamin D₃ metabolites. Employing this sensitive method the presence of receptors for 1,25(OH)₂D₃ in the mature rat uterus was evident. Such receptors were not found in the uterus of saline-treated immature rats. However, oestradiol administration caused an induction of these receptors in the immature rat uterus, together with a significant increase in the uterine weight, progesterone receptor level and peroxidase activity. These results suggest a mechanism for oestradiol regulation of calcium metabolism in the uterus at times of high demand for this cation during the gestation period.