BONE ENDOTHELIAL-CELLS AS ESTROGEN TARGETS

In the present study, we investigated the effects of estrogens on bone endothelial cell metabolism and the presence of estrogen binding site s in the same cells. For these studies, we have used a continuous cell line of clonal bovine bone endothelial cells for evidence of a direct response to estrogens in vitro. Receptor analysis to intact viable ce lls was steroid specific and saturable, with an apparent dissociation constant of 17.2 nM and a B(max) of 3.2 x 10(4) sites/cell. Northern b lot analysis revealed a 6.5-kilobase mRNA that hybridized with a cDNA to human estrogen receptor. The 6.5-kilobase size is in close agreemen t with the reported size of the human estrogen receptor mRNA. In vitro estrogen responses of bone endothelial cells included a stimulation o f cell proliferation as well as an inhibition of parathyroid hormone r esponsiveness. These findings clearly demonstrate the presence of func tional estrogen receptors in bone endothelial cells in vitro, suggesti ng a role of estrogens in bone angiogenesis and in the entire process of bone remodeling.