OVARIECTOMY-INDUCED BONE LOSS AND THE HEMATOPOIETIC SYSTEM

To investigate the relationship of the hematopoietic system to the los s of bone due to ovarian hormone deficiency, we examined the effects o f ovariectomy and estrogen administration on the thymus, spleen and th e bone marrow, and on the proliferation of marrow progenitor's of oste oclasts. We also assessed the effects of daily administration of inter leukin-l receptor antagonist (IL-1ra) on bone loss due to ovarian horm one deficiency. Ovariectomy resulted in decreased cancellous bone volu me, increased trabecular osteoblast and osteoclast numbers, and increa sed serum alkaline phosphatase levels that were prevented by 17 beta-e stradiol treatment. Thymus weight, spleen weight, thymus and spleen ly mphocytes, and bone marrow monocytes and lymphocytes also increased si gnificantly following ovariectomy, and the increases were suppressed b y 17 beta-estradiol. Ovariectomy, in addition, caused a 4-fold increas e in the number of tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells formed in cultures of marrow cells and the incre ase was partially inhibited by 17 beta-estradiol. IL-1ra administratio n did not prevent the bone loss due to ovariectomy. Our findings indic ate that ovariectomy-induced bone loss in the rat is accompanied by ma rked changes in the hematopoietic system, and that these changes are m odulated by estrogen administration. In spite of the negative finding with IL-1ra, the nature of the involvement of the hematopoietic system in the pathogenesis of bone loss due to ovarian hormone deficiency me rits continued exploration.