EVIDENCE THAT ESTROGEN BINDING-SITES ARE PRESENT IN BONE-CELLS AND MEDIATE MEDULLARY BONE-FORMATION IN JAPANESE-QUAIL

Studies were carried out in Japanese quail to characterize the binding of estrogen to bone cells and to determine whether induction of medullary bone by estrogen is mediated by estrogen receptors. First, attempts were made to identify specific, high affinity nuclear binding sites for estrogen with a nuclear exchange assay in oviduct and femora from laying female quail and in liver, kidney, and femora from adult male quail treated with estradiol valerate (2 mg per bird). High-affinity nuclear estrogen binding sites were detected in each of the tissues except femora. Second, estrogen binding sites in femora from male quail were localized by radioautography after treatment with 100 muCi of [H-3]-17beta-estradiol ([H-3]-E). Estrogen binding sites were present at 1 and 3 h after administration of [H-3]-E, and binding of the radiolabeled hormone was prevented by the simultaneous administration of an excess of radioinert estrogen. Third, estradiol valerate (.4 mg) was given as a bolus to adult male Japanese quail. Five days later, the quail had hypercalcemia due to accumulation of phosvitin in serum, had an extensive network of medullary bone at the femur midshaft, and had reduced cortical bone area. The nonsteroidal, anti-estrogen tamoxifen (2 mg/day) prevented estrogen-induced hypercalcemia, medullary bone formation, and reduction of cortical bone area. Fourth, the estrogen target cells in femora from adult male quail that were induced to differentiate to osteoblasts by estrogen treatment were located by [H-3]-proline radioautography as early as 12 h following administration of the hormone. These results are interpreted as evidence that induction of medullary bone is a process mediated by estrogen receptor.