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Approximately 15% of our highly inbred C57BL/6 mice show a spleen with a pigmented cranial part. Microscopically, abundant aggregates of pigment granules are observed primarily scattered between cells of the red pulp. They give a positive reaction with Perls' Prussian blue and stain heavily with silver-methenamine. Most of the granules are stored in macrophages. In some cases a number of granules are surrounded by a membrane. This abnormality may be designated haemosiderosis. In the present study we demonstrate that it is not related to the consumption of iron within the range normally found in laboratory animal diets. This suggests a genetic origin, although confirmation would require further research. If so, comparison with human idiopathic haemochromatosis is tempting. However, contrary to the human condition, organs other than the spleen are not affected, with exception of the liver. This organ contains minor deposits of pigment granules. Nor do affected animals appear to show any ill effects. Nevertheless, it seems worthwhile to investigate whether this phenomenon in C57BL mice could serve as a model for the human disease provided that a practical criterium becomes available for detection in the intact animal.

Female Wistar rats (n = 11) received bleomycin 10 mg kg-1 i.p. three times weekly for 6 weeks. Four weeks later part of the group (n = 7) were exposed to 50% oxygen in air for 4 h; the others served as unexposed controls. A further control group (n = 5) received physiological saline i.p. and was not exposed to oxygen. One week after the hyperoxia treatment all animals were sacrificed and the lungs prepared for histological and biochemical determinations. Although the average body weight of the bleomycin-treated rats decreased significantly compared with the saline-treated controls, no significant alterations in lung histology were found in regard to the occurrence of oedema, fibrosis, and type II pneumocytes. Intra-alveolar macrophages were significantly increased. Subsequent hyperoxia did not lead to a more pronounced effect, except for macrophage accumulation. The activities of superoxide dismutase and glutathione peroxidase were not changed either after administration of bleomycin alone or after combination with hyperoxia. It is concluded that bleomycin i.p. in doses comparable to those encountered clinically, administered alone or combined with hyperoxia, does not result in pulmonary damage in female Wistar rats.