Bone marrow reactions of young and old rats to chemical stressors

Abstract The myelograms of rats aged 4–6 months and 24–30 months and the reactions of the bone marrow to ACTH and chemical stressor (endotoxin) were studied. In the old untreated rats the number of eosinophil granulocytes decreased considerably, the plasma cells increased in number, and the mitotic index for the bone marrow cells was lower than in the young animals. After the action of the chemical stressors bone-marriw neutropenia and eosinophilia occurred in both age groups, but were more marked in the old animals. At electron-microscopy, as against controls, endotoxin gave rise to a considerable number of rather large-sized Russell bodies in the plasma cells of the bone marrow of the young rats. The fact that this reaction was less pronounced in the old animals might be a possible explanation for the decline in intensity of the immunoreaction in old age.