HEMOGLOBIN BREAKDOWN AND HEMOPOIESIS 625 



5.2. Influence of Oxygen Tension and Anoxia 

 of the Bone Marrow on Hemopoiesis 



In 1890 Viault {2875) observed an increase of hemoglobin after 

 ascent to high altitudes. It was later studied extensively by Barcroft 

 {IJ^O), cf. also Hurtado and co-workers {1372,1373). This effect is 

 due to the lowered oxygen tension, incomplete saturation of the 

 hemoglobin with oxygen, and anoxia of the bone marrow acting as 

 a stimulus to hemopoiesis. It can be produced experimentally in 

 low-pressure chambers. The polycythemia of patients with pul- 

 monary or cardiac diseases, that caused by administration of vaso- 

 constrictor drugs {cf. 54-3), and perhaps also that caused by cobalt 

 are also due to anoxia of the bone marrow. Polycythemia vera, a 

 disease in which both red cell numbers and hemoglobin are greatly 

 increased, has also been explained as due to the effect of arterioscle- 

 rosis on the oxygen supply of the bone marrow. The mechanism by 

 which the anoxia of the bone marrow increases hemopoiesis is still 

 unknown.* It has been suggested that hemopoiesis is sensitive to 

 alteration in oxygen tension rather than to its absolute value {2285). 

 This does not appear to be correct since dwellers at high altitudes 

 show higher average hemoglobin concentrations and red cell counts 

 than dwellers at sea level. The primary stimulus appears to be on 

 hemoglobin formation rather than cytopoiesis, since the mean cor- 

 puscular hemoglobin increases before the erythrocyte count {2665). 

 This is also supported by the observation of Hurtado and co-workers 

 {1372), who observed an increase of myohemoglobin in dogs exposed 

 to low oxygen tension. Conversely bone marrow activity and retic- 

 ulocyte number are depressed by high oxygen pressure, by vasodila- 

 tion caused by acetylcholine, or by raising the hemoglobin level above 

 normal by blood transfusions {261 ,51^2 ,1369 ,2285) , but some workers 

 have been unable to find an effect of increased oxygen tension on 

 hemoglobin regeneration. 



5.3. Direct Relations between Hemoglobin Breakdown 

 and Hemopoiesis 



In addition to an indirect stimulus to hemopoiesis via anoxia in 

 the bone marrow when abnormal hemoglobin breakdown occurs, the 



* Anoxia in vivo may cause an "anoxic hyperoxia" by increase of respiration, 

 arterial pressure, and cardiac rate. Rosin and Rachmilewitz {2S!t'2a) found that low 

 oxygen tension decreased, and high oxygen tension increased, the rate of cell matura- 

 tion and multiplication in bone marrow explants. 



