Blood Gas Tensions and Acid-Base Regulation in the Salt-Water Crocodile, Crocodylus Porosus, at Rest and After Exhaustive Exercise

Salt-water crocodiles, Crocodylus porosus Schneider, were catheterized and Po₂, Pco₂, pH and lactate concentration ([lactate]) were measured in arterial blood during rest and after forced exhaustive activity at 30°C.

Gas exchange ratio (R), calculated from blood Po₂ and Pco₂, decreased from about 1.0 to 0.3 during resting voluntary breath-holding and indicated CO₂ sequestration in the body fluids. The mean value for R in undisturbed animals was 0.6, which substantiates the hypothesis that some CO₂ excretion is extrapulmonary.

In vitro buffer value of true plasma was −23.5±1.9 mmol HCO₃-1⁻¹ pH⁻¹. In vivo buffer value, determined by short-term self titration with metabolic CO₂, was −12.2±4.7mmolHCO₃-1⁻¹ pH⁻¹.

Exhaustive activity for 5 min in laboratory animals resulted in pronounced metabolic lactacidosis: pH decreased approximately from 7.43 to 7.11 while lactate concentration increased from 1.2 to 20–30 mmoll⁻¹. The acidosis was reduced by respiratory compensation during the first hour of recovery and by metabolic adjustments that were practically complete after the third hour. Greater acidosis (pH down to 6.4) in larger field-captured animals was resolved over a longer period.

During recovery, lactate and proton fluxes between the blood and other tissue were uncoupled.

The virtual absence of the fixed-acid Bohr effect in C. porosus blood is adaptive in large individuals because it facilitates continued O₂ uptake from the lung into blood which may be acidified by as much as 1 pH unit as a result of physical activity.