Comparative study of the oxyhaemoglobin dissociation curve of four mammals: man, dog, horse and cattle.

1. The entire oxygen dissociation curve (ODC) and the effects of temperature, pH and 2,3-diphosphoglycerate (DPG) on this curve, have been compared in four mammalians: man, dog, horse and cattle. 2. If the oxyphoric capacities are similar between these species (around 1.39 ml O2/gHb), their P50, measured in standard conditions, i.e. at pH 7.4; pCO2 40 mmHg and T 37 degrees C, varies between 23.8 (+/- 0.8) mmHg for the horse, 25.0 (+/- 1.4) mmHg for cattle, 26.6 (+/- 1.2) for man and 28.8 (+/- 2.6) mmHg for the dog. 3. The higher dispersion of the dog's P 50 is due to difference between breeds; in seven breeds investigated, the P 50 ranges from 25.8 (spaniel) to 35.8 (hound). 4. We noted no sex difference in the four species. 5. The DPG level is confirmed to be low in cattle (< 1 mumol/gHb) as compared to man (13.5 +/- 2.1 mumol/gHb), horse (16.9 +/- 1.1 mumol/gHb) and dog (19.4 +/- 2.8 mumol/gHb). 6. The oxygen exchange fraction defined as the difference in vol% between a pO2 of 80 and 35 mmHg is, respectively, 3.6 (+/- 0.6) vol% for cattle, 4.0 (+/- 0.4) vol% for the horse, 5.5 (+/- 0.5) vol% for man and 6.6 (+/- 1.7) vol% for the dog. 7. The position and shape of the ODC, as well as T, DPG and pH effects, indicate that the haemoglobin of man and dog seem better adapted to O2 delivery as compared to the horse and cattle.