Recovery from an activity-induced metabolic acidosis in the American alligator, Alligator mississippiensis

Abstract

The metabolic acidosis resulting from an intense exercise bout is large in crocodilians. Here we studied recovery from this pH perturbation in the American alligator. Metabolic rate, minute ventilation, arterial pH and gases, and strong ion concentration were measured for 10 h after exhaustion to elucidate the mechanisms and time course of recovery. Exhaustion resulted in a significant increase in lactate, metabolic rate, and ventilation, and a decrease in arterial PCO2, pH and bicarbonate. By 15 min after exhaustion, oxygen consumption returned to rest though carbon dioxide excretion remained elevated for 30 min. Arterial PO2, [Na+], and [K+], increased following exhaustion and recovered by 30 min post-exercise. Minute ventilation, tidal volume, [Cl−], and respiratory exchange ratio returned to resting values by 1 h. The air convection requirement for oxygen was elevated between 15 and 60 min of recovery. Breathing frequency and pH returned to resting values by 2 h of recovery. Lactate levels remained elevated until 6 h post-exercise. Arterial PCO2 and [HCO3−] were depressed until 8 h post-exercise. Compensation during recovery of acid-base balance was achieved by altering ventilation: following the initial metabolic acidosis and titration of bicarbonate, a relative hyperventilation prevented a further decrease in pH.