Wouldn’t this be a boon for athletes? :dubious:
Higher oxygen affinities at equivalent partial pressures compared to adult hemoglobin --> more oxygen delivered to muscles --> less anaerobic respiration --> less lactate and hydrogen ions --> less muscle pain and fatigue --> greater performance?
No, it wouldn’t. Adult hemoglobin’s affinity for oxygen is selectively reduced by 2,3-bisphosphoglyceric acid, which ultimately increases oxygen release in tissues where it’s required; in the absence of BPG, adult hemoglobin’s affinity for oxygen is actually higher than fetal hemoglobin’s. Fetal hemoglobin does not bind BPG as strongly, and consequently does not release oxygen as readily. This could cause hypoxia in low oxygen conditions such as high altitude (where BPG levels are normally higher), especially in tissues with high oxygen demand. While the condition is usually regarded as benign, and downright beneficial in people with certain hemoglobin-related pathologies such as sickle-cell anemia, I would expect negative consequences in athletes, who routinely place higher demands on their ability to deliver oxygen to tissues.
The reason for this difference in binding ability is that in the fetus, the fetal circulation is taking the oxygen from the maternal red blood cells that already have bound oxygen. It is better for them to have a better affinity, so the oxygen prefers to be with them (and then nourish the fetus) than with the mom, who already has a good way of taking oxygen (by air).
In contrast, there is plenty of oxygen when one inspires and breathing normally, that the lesser affinity to oxygen in the adult red blood cells is not an issue, to the contrary, it is better because then the red blood cells can release the oxygen much better to the rest of the body that needs oxygen (and then quickly return to circulation and make the trip to the lungs again).
The fetal hemoglobin is less likely to release the bound oxygen than the adult hemoglobin, but the fetal organs require much less oxygen than the adult, working, and moving counterparts.