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 sites 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 cells was steroid specific and saturable, with an apparent dissociation constant of 17.2 nM and a Bmax of 3.2 x 10(4) sites/cell. Northern blot analysis revealed a 6.5-kilobase mRNA that hybridized with a cDNA to human estrogen receptor. The 6.5-kilobase size is in close agreement with the reported size of the human estrogen receptor mRNA. In vitro estrogen responses of bone endothelial cells included a stimulation of cell proliferation as well as an inhibition of parathyroid hormone responsiveness. These findings clearly demonstrate the presence of functional estrogen receptors in bone endothelial cells in vitro, suggesting a role of estrogens in bone angiogenesis and in the entire process of bone remodeling.