title: The ultrastructural effect of estrogens on bone cells in thyroparathyroidectomized rats.
abstract: To determine the direct effect of estrogen on bone cells, female rats were thyroparathyroidectomized and given either 200 microng of estradiol cypionate or placebo treatment for 4 to 30 days. After 8 days, an osteosclerosis of the tibial metaphysis developed in rats treated with estrogens. Osteoblasts in estrogen-treated rats were interpreted ultrastructurally to be less active in bone formation than controls. Osteocytes in estrogen-treated rats were inactive compared to osteocytes in control rats which were continuing the process of bone formation. Osteoclasts were decreased in numbers in rats treated with estrogen; however, the electron microscopic characteristics of osteoclasts did not differ from controls. These cellular changes were associated with a severe hypocalcemia in both estrogen-treated and control rats. Serum phosphorus and urinary hydroxyproline were lowered significantly by the administration of estrogen. It is concluded that metaphyseal osteosclerosis develops in estrogen-treated rats independent of parathyroid hormone and calcitonin. The osteoclerosis is due to an effect of estrogens to reduce osteoclast-numbers and a lesser inhibitory effect on the bone-forming activity of osteoblasts and osteocytes. (Am J Pathol 87:311-322, 1977).
mesh_terms: D000818:Animals; D002452:Cell Count; D004958:Estradiol / Q000494:pharmacology; D004967:Estrogens / Q000009:adverse effects / Q000494:pharmacology*; D008297:Male; D010006:Osteoblasts / Q000187:drug effects; D010010:Osteoclasts / Q000187:drug effects; D010011:Osteocytes / Q000187:drug effects*; D010026:Osteosclerosis / Q000139:chemically induced; D010280:Parathyroid Glands / Q000601:surgery*; D010919:Placebos; D051381:Rats; D013965:Thyroidectomy; D013997:Time Factors
chemical_list: D004967:Estrogens; D010919:Placebos; D004958:Estradiol