ULTRASTRUCTURAL EFFECT OF ESTROGENS ON BONE-CELLS IN THYROPARATHYROIDECTOMIZED RATS

  • 1 January 1977
    • journal article
    • research article
    • Vol. 87  (2) , 311-322
Abstract
To determine the direct effect of estrogen on bone cells, female rats were thyroparathyroidectomized and given either 200 .mu.g of estradiol cypionate or placebo treatment for 4-30 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, EM 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 P and urinary hydroxyproline were lowered significantly by the administration of estrogen. Metaphyseal osteosclerosis develops in estrogen-treated rats independent of parathyroid hormone and calcitonin. The osteosclerosis is due to an effect of estrogens to reduce osteoclast numbers and a lesser inhibitory effect on the bone-forming activity osteoblasts and osteocytes.

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