ESTROGEN TARGET-CELLS DURING THE EARLY STAGE OF MEDULLARY BONE OSTEOGENESIS - IMMUNOHISTOCHEMICAL DETECTION OF ESTROGEN-RECEPTORS IN OSTEOGENIC CELLS OF ESTROGEN-TREATED MALE JAPANESE-QUAIL

The localization of estrogen receptors (ER) in osteogenic cells during the early stage of medullary bone osteogenesis was studied immunohistochemically in the femurs of estrogen-treated male Japanese quail. Alkaline phosphatase (ALP) activity was used as a marker for osteogenic cells. ER immunostaining was observed in the nuclei of weak ALP-positive bone lining cells on the endosteal bone surface of nontreated birds. After 24 hours of estrogen treatment, nuclear immunostaining was detected in ALP-positive preosteoblasts on the endosteal bone surface. After 48 hours, the medullary bone appeared to some degree along the endosteal surface. ER immunostaining was observed in the nuclei of ALP-positive osteoblasts on the medullary bone surface. This study demonstrates that ER are present in osteogenic cells, and suggests that estrogen directly acts on medullary bone osteogenesis.