EOSINOPHILS IN THE BONE MARROW OF NORMAL AND CORTISOL-TREATED RATS Quantitative and Autoradiographic Studies

Absolute counts of the eosinophil cells of the blood and bone marrow were carried out in a haemocytometer and combined with autoradiographic studies of smears of blood and bone-marrow suspensions from normal rats and cortisol-treated rats. A certain parallelism was found between the number of circulating eosinophil leucocytes and the eosinophils of the bone marrow. Calculations showed that the bone marrow contains more than 50 times as many eosinophils as the blood. Single injections of Cortisol (5 mg intraperitoneally) as well as repeated injections of Cortisol (5 mg every 6 hours for up to 3 days) induced blood and bone-marrow eosinopenia. The decrease in the number of eosinophils in the bone marrow appears to be due primarily to a decrease of mature (non-prolifera ting) eosinophils. During repeated injections there was continued proliferation of eosinophil cells in the bone marrow, but mitotic activity was reduced. Appearances like those in the bone marrow have previously been observed in the spleen (Bro-Rasmussen 1972 and 1973).