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

Abstract

ABSTRACT Salt-water crocodiles, Crocodylus porosus Schneider, were catheterized and , 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 and , 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 +1·9mmol HCO2−I−1 pH−1. In vivo buffer value, determined by short-term self titration with metabolic CO2, was – 12·2 + 4·7mmolHCOs− I−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 mmol I−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.