Oxygen and Carbon Dioxide Transport Characteristics of the Blood of the Nile Monitor Lizard (Varanus Niloticus)

Oxygen and carbon dioxide dissociation curves were constructed for the blood of the Nile monitor lizard, Varanus niloticus, acclimated for 12h at 25 and 35°C. The oxygen affinity of Varanus blood was low when Pco₂ w a s in the range of in vivo values (25°C: P₅₀ = 34.3 at P_COCO2 = 21 mmHg; 35°C: P₅₀ = 46.2 mmHg at P_COCO2 = 35 mmHg; 1 mmHg = 133.3 Pa), and the oxygen dissociation curves were highly sigmoidal (Hill's n = 2.97 at 25°C and 3.40 at 35°C). The position of the O₂ curves was relatively insensitive to temperature change with an apparent enthalpy of oxygenation (ΔH) of −9.2kJ mol⁻¹. The carbon dioxide dissociation curves were shifted to the right with increasing temperature by decreasing total C_COCO2 at fixed P_COCO2, whereas the state of oxygenation had little effect on total blood CO₂ content. The in vitro buffer value of true plasma (Δ[HCO₃⁻]_pl/-ΔpH_pl) rose from 12.0 mequiv pH⁻1⁻¹ at 25°C to 17.5 mequiv pH⁻¹1⁻¹ at 35°C, reflecting a reversible increase of about 30% in haemoglobin concentration and haematocrit levels during resting conditions in vivo.