Effects of Ovariectomy and 17β-Estradiol on Bone GLA Protein in Growing Rats: An Indirect Evidence for Estrogen Receptors in Bone Cells

Estrogen deficiency after ovariectomy in the rat is followed by an increase of bone turnover and bone loss. Estrogens are thought to modulate the sensitivity of skeleton to Parathyroid Hormone; according to the recently reported evidence of estrogen receptors on osteoblasts, however, a direct effect on bone cells should not be ruled out. We studied the behaviour of Bone Gla Protein (Osteocalcin), a reliable marker of osteoblast function, in growing rats after ovariectomy and treatment with 17 beta-estradiol. Results indicate that ovariectomy stimulates, as expected, bone turnover, and that estrogen induces a further increase of osteoblast activity revealed by the rise of Bone Gla Protein plasma levels. This data may have clinical implications in humans, where estrogens are currently suggested for prevention and therapy of post menopausal osteoporosis.