Adaptation of mice to carbon monoxide and the effect of splenectomy

The adaptation of normal and splenectomized mice to increasing concentrations of carbon monoxide (CO) in air, and their subsequent long-term survival in it were studied. From the 10th day onwards the concentration of CO was maintained at 0.24%, which produced a carboxyhaemoglobin level of about 74% in the blood, and which was normally lethal within 24 h. However, the non-splenectomized mice survived in this envirment for an average of 47 days, but splenectomized moce survived for 101 days. During adaptation to CO there were marked increases in the haematocrit level and the concentration haemoglobin, a massive release of reticulocytes into the circulation, and increases in blood volume, spleen and heart weight. However, changes in the above haematological parameters were significantly less in splenectomized than in normal animals. These differences were attributed to the loss of the erythropoietic reservees of the spleen. In splenctomized mice which survived for over 90 days in CO there was histological evidence for the development of extramedullary erythropoiesis, as well as increased erythropoietic activity in the marrow of the tail vertebrae, which occurred earlier. Deaths were most frequently associated with massive internal haemorrhages in both groups of animals. This is discussed in relations to histological and haematological findings. Also in both groups, there was evidence that both hypertrophy and hyperplasia of heart muscle fibres occurred during adaptation to breathing CO.