The respiratory properties of blood from voluntarily diving Xenopus seem well matched to the animal's habit of ventilating its lungs in an intermittent fashion. Compared with more terrestrial anurans, the high oxyhaemoglobin affinity (P50 = 29.6 Torr, pH 7.73, 25°C), Bohr effect (δlogP50/δpH = −0.37) and Haldane effect (0.37 mol CO2mol−1 O2) can be viewed collectively as adaptations towards effective blood gas storage during periods of apnoea and blood gas exchange during episodes of air breathing. It appears, therefore, that these biochemical adaptations are linked to the changes in respiratory blood flow that are made possible by the partially divided double circulation of Xenopus.

In comparison with blood from voluntarily diving Xenopus, that taken from animals at the end of a 30-min enforced dive was haemoconcentrated and contained 4 and 8mmoll−1 higher concentrations of true plasma lactate and metabolic acid equivalents respectively. The pH-induced effects of the latter led to reductions in oxyhaemoglobin affinity and blood CO2 carriage, both of which persisted for up to 4h following emergence from an enforced dive. The associated haemoconcentration led to a secondary series of effects of which the most obvious were an elevated blood oxygen-carrying capacity and an increased non-bicarbonate buffer slope for true plasma. Marked changes, such as these, were never observed in blood samples taken at various stages of voluntary dives lasting upwards of 30 min.

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