Oxygen dissociation properties of human embryonic red cells.

Abstract

THERE are three stages in the development of human haemoglobins. In the smallest embryos studied the embryonic haemoglobins, Hb-Gower 1, Hb-Gower 2 and Hb-Portland are the main haemoblobins found1, but foetal haemoglobin (Hb-F) is also present in gradually increasing amounts. By about the 30 mm (crown–rump (CR) length) stage, Hb-F amounts to about 50% of total haemoglobin and after 50 mm it forms over 90% of total pigment. Adult haemoglobin (Hb-A) is already present by week 8 of gestation but this does not exceed 10% of total haemoglobin until week 30; after this it gradually increases until at term it forms between 10% and 30%. After birth, Hb-F is rapidly replaced by Hb-A and at 6 months Hb-F is less than 10%, while at one year it forms less than 2% of total haemoglobins. The oxygen dissociation properties of adult haemoglobin and of foetal haemoglobin have been studied in great detail. Foetal blood has a higher oxygen affinity than adult blood; this helps the transport of oxygen across the placenta and ensures that the steep part of the oxygen dissociation curve corresponds to foetal tissue oxygen tensions, thus maximising the release of oxygen. The oxygen affinities of the human embryonic haemoglobins have so far not been studied because the amounts available have been extremely small. Here we describe the oxygen dissociation properties of human embryonic red cells which were found to be similar to those of foetal red cells.