Spontaneous Bone Marrow Granulomas in Rats

—Effect of Ovariectomy on Granulomas Formation—

Abstract

Spontaneous granulomas developed frequently in the bone marrow of Slc: Wistar female rats over 19 weeks of age, whereas none did in JCL: SD and Slc: SD rats of either sex. These granulomas were composed histologically of epithelioid cells and macrophages clustered mostly in the center and lymphocytes and plasma cells located in the periphery, and they contained neither microorganisms nor foreign bodies. Ovariectomy of Slc: Wistar rats at 6 weeks of age resulted in a significant decrease in the incidence and size of bone marrow granulomas at 20 and 24 weeks of age. It is concluded that two factors, the strain of rats and female sex hormone, contribute to the pathogenesis of bone marrow granulomas-the former as a hereditary disposition and the latter as a promoter.