Haemoglobin oxygen affinity and regulating factors of the blood oxygen transport in canine and feline blood

Complete dynamic oxygen equilibrium curves (OEC) on dogs and cats whole blood were measured at 33, 37 and 41 degrees C. OEC were also run at three partial carbon dioxide pressures (20, 40 and 80 mmHg) as well as at five pH levels (7.2, 7.3, 7.4, 7.5 and 7.6). 2,3- diphosphoglycerate (DPG) concentrations were determined. Results were compared to those previously published in humans, using the same experimental method [Comp. Biochem. Physiol. 106 (1993) 687]. In standard conditions (pH 7.4, pCO2 40 mmHg and temperature 37 degrees C), the partial oxygen pressure at half-saturation of haemoglobin (p50) was 30.0+/-1.3 mmHg for dogs and 34.1+/-1.8 mmHg for cats. Cat's OEC was thus rightshifted compared to dog's OEC, itself rightshifted compared to human OEC. 2,3-DPG concentrations were higher in dogs than in men until they were very low in cats. Contrary to that observed in human medicine, no significant correlation was identified between standard p50 and canine 2,3-DPG values. Influence of pH, pCO2 and temperature on the OEC was saturation dependent. In dogs, Delta log p50/Delta pH was equal to -0.370, Delta log p50/Delta log pCO2 was 0.093 and Delta log p50/Delta T was 0.020. In cats, Delta log p50/Delta pH was equal to -0.405, Delta log p50/Delta log pCO2 was 0.080 and Delta log p50/Delta T was 0.016. Practically, temperature and pH variations exert a lesser influence in domestic carnivores than in humans, effect of pCO2 being similar in both.