Ventilation and acid-base balance during graded activity in lizards

Area of Science:

• Physiology
• Comparative Physiology
• Exercise Physiology

Background:

• Understanding acid-base balance in reptiles is crucial for comprehending their physiological responses to environmental challenges and physical exertion.
• Reptiles exhibit unique metabolic and respiratory strategies that differ from endotherms, necessitating specific investigations into their exercise physiology.

Purpose of the Study:

• To investigate the acid-base regulation mechanisms in lizards (Varanus exanthematicus and Iguana iguana) during treadmill exercise.
• To determine the relationship between metabolic rate, lactate accumulation, and ventilatory responses in these species under varying exercise intensities.

Main Methods:

• Measurements of arterial PCO2, hydrogen ion concentration, lactate concentration, CO2 production (VCO2), O2 consumption (VO2), and effective alveolar ventilation (Veff) were conducted.
• Lizards were subjected to steady-state treadmill exercise at a controlled temperature of 35°C.

Main Results:

• In Varanus, increased VCO2 and VO2 at lower speeds led to enhanced ventilation, decreasing PaCO2 and [H+]a without significant lactate rise.
• At higher exercise intensities, lactate ([L]a) increased, triggering hyperventilation that maintained [H+]a near resting levels until further lactate accumulation caused acidosis.
• Iguana showed similar patterns, with ventilation compensating for metabolic demands and lactate accumulation to preserve acid-base homeostasis at sustainable speeds.

Conclusions:

• Both Varanus and Iguana demonstrate effective blood acid-base homeostasis during moderate exercise through ventilatory adjustments.
• These findings highlight the capacity of these lizard species to manage metabolic byproducts and maintain physiological stability during physical activity.