MARROW CELL INJURY FOLLOWING Ca⁴⁵ UPTAKE IN BONE: CHANGES IN MARROW AND PERIPHERAL BLOOD CELLULARITY

¹ From the Department of Radiological Sciences, The Johns Hopkins University, School of Hygiene and Public Health, Baltimore, Maryland

The amounts of Ca⁴⁵ used in these experiments were small and the calculated radiation doses through the first 6 days when the most drastic hematologic changes were observed were low compared to x-ray doses used in other experiments to perturb the normal steady state of the bone marrow. Nevertheless, the changes produced within the bone marrow in these rats receiving Ca⁴⁵ were as great, or greater in some instances, as those caused by larger x-ray doses.

Radiation from Ca⁴⁵ incorporated into the bones of the rats, caused cell death and accelerated cell removal within the mature marrow granulocyte pool. Mitotic delay or inhibition of the rapidly dividing and differentiating precursor cells plus the radiation-induced cell death caused a rapid and extensive decrease in the number of nucleated cells of the marrow.

Since there were fewer mature cells in the marrow to cope with natural attrition rates in the peripheral blood, granulocytopenia resulted. Being unable to deliver mature cells for circulation, the marrow released large numbers of immature granulocytes, (bands), and reticulocytes into the blood. Until regeneration in the marrow is relatively advanced, a period follows when immature cells of the marrow predominate.

Recovery approaches normal by 5 months after Ca⁴⁵ injection but cannot be considered to be complete since the Ca⁴⁵ is relatively fixed in the bone and will continue to cause radiation damage. Radium, strontium, and other bone seeking radioisotopes can replace calcium in the bone and can be expected to produce the same relative results in the bone marrow.

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