Variation in acid-base regulation in vertebrate ectotherms

Acid-base regulation in air-breathing ectotherms is remarkably variable. Some reptiles maintain arterial pH within very narrow limits while others allow large changes in arterial pH during acid-base perturbations (e.g., change in body temperature, secretion of HCl for digestion, and exercise). The experiments described in this dissertation were designed to examine the causes and consequences of variability in acid-base regulation.; To examine the consequences of pH variability, enzyme activity was measured over a range of incubation pH in skeletal muscle of bullfrogs, cane toads, and black racer snakes. Over a 20-degree temperature range (10°C--30°C), enzyme activity was not restricted to the narrower pHi range measured in the skeletal muscles of these animals. Therefore, loss of enzyme function is not one of the primary consequences of variability in acid-base regulation in these animals.; Two of the causes of pH perturbation include exercise and digestion. To understand how some air-breathing ectotherms recover from large acid-base perturbations, two experiments were designed to induce a metabolic acidosis and alkalosis. Savannah monitor lizards experience a significant metabolic alkalosis during the first days of digesting a large meal. The alkalosis is partially compensated by a relative hypoventilation. American alligators experience a large metabolic acidosis during and immediately following an intense activity bout, which lasts for several hours. This acidosis is partially compensated by a relative hyperventilation.; Altering ventilation appears to be a primary mechanism for regulating acid-base status during and after a pH perturbation. Therefore, an experiment was designed to examine the response to acid-base perturbing situations when the recovery mechanism is compromised. Crocodilians can use a hepatic piston pump to alleviate the potential axial constraint associated with simultaneous use of hypaxial musculature during locomotion and ventilation. Alligators were able to maintain ventilation and oxygen consumption during rest and activity when the hepatic piston was removed, suggesting that either other breathing mechanisms are compensating for the loss of the hepatic piston, or that its role in ventilation is relatively minor in alligators. The variability observed in these experiments suggests that the ability to compensate for disturbances to the physiology of these animals is quite diverse.