Genetic Relationship between Fetal Hb Levels in Normal and Erythropoietically Stressed Baboons

Summary. Previous studies have shown that the magnitude of the fetal haemoglobin (Hb F) response to haemolytic anaemia and hypobaric hypoxia in the baboon is specific to an animal (‘high and low Hb F responders’), suggesting that the Hb F response is under genetic control. In this study Hb F levels in 55 adult (over 8 years old) and 23 juvenile unstressed baboons varied between 0·02% and 0·6% (‘resting Hb F levels’). Twenty‐nine of these animals were subjected to haemolytic stress and the magnitude of their Hb F response was positively correlated with the resting Hb F levels. In addition, the resting levels of Hb F in parents were positively correlated with those of their offspring. In 11 animals, seven adults and four juveniles, subjected to haemopoietic stress the Hb F levels were increased proportionally to the number of F‐cells. In juvenile animals the calculated concentration of Hb F per F‐cell was markedly higher than in adult animals. These data demonstrate that the resting level of Hb F is predictive of the magnitude of the Hb F response to stress erythropoiesis. The number of F‐cells and the concentration of Hb F per cell in erythropoietic stress appear to be modulated by different mechanisms.