Ovariectomy augments B lymphopoiesis and generation of monocyte-macrophage precursors in rat bone marrow

To investigate the effects of estrogen depletion on hematopoiesis and bone turnover, female rats were either ovariectomized (OVX) or sham operated and killed at 1, 2, 3, and 4 wk postsurgery. Flow cytometric analysis of bone marrow cells (BMC) revealed that, in close temporal association with the rise in bone turnover as measured by bone histomorphometry, the number of Thy 1.1+ and KiB1R+ BMC increased two- to threefold in OVX rats relative to sham controls. The Thy 1.1+ BMC were further characterized as Thy 1.1+/KiB1R+ and Thy 1.1+/HIS24+ double-positive cells of the B cell lineage. A transient rise in ED1+ myeloid cells expressing a lysosomal antigen specific for the monocyte-macrophage and osteoclast lineage coincided with the upregulation of osteoclast numbers in OVX rats at 2 wk postsurgery, but the number of ED8+ myelomonocytic BMC remained unchanged. Administration of estradiol prevented the rise in Thy 1.1+, KiB1R+, and ED1+ BMC in OVX animals. Our study indicates that ovariectomy upregulates B lymphopoiesis in rat bone marrow and increases myeloid cell differentiation into the monocyte-macrophage and possibly also the osteoclast lineage.