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 was in the range of in vivo values (25°C: P50 = 34·3 at 35°C: P50 = 46·2mmHg at 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 −9·2kJmol−1. The carbon dioxide dissociation curves were shifted to the right with increasing temperature by decreasing total at fixed , whereas the state of oxygenation had little effect on total blood CO2 content. The in vitro buffer value of true plasma (Δ [HCO3−]pl/−ΔpHp1) rose from 12·0mequivpH−11−1 at 25°C to 17·5 mequivpH−11−1 at 35°C, reflecting a reversible increase of about 30 % in haemoglobin concentration and haematocrit levels during resting conditions in vivo.