AJP - Regulatory, Integrative and Comparative Physiology, Vol 240, Issue 1 29-R37, Copyright © 1981 by American Physiological Society
Ventilation and acid-base balance during graded activity in lizards
G. S. Mitchell, T. T. Gleeson and A. F. Bennett
Arterial PCO2, hydrogen ion ([H+]a), and lactate ([L]a) concentrations,
rates of metabolic CO2 production (VCO2) and O2 consumption (VO2), and
effective alveolar ventilation (Veff) were determined in the lizards
Varanus exanthematicus and Iguana iguana at rest and during steady-state
treadmill exercise at 35 degrees C. In Varanus, VCO2 increased ninefold and
VO2 sixfold without detectable rise in [L]a at running speeds below 1.0 to
1.5 km x h-1. In this range, Veff increased 12-fold resulting in decreased
levels of PaCO2 and [H+]a. At higher speeds [L]a rose. Increments of 5 mM
[L]a were accompanied by hyperventilation, reducing PaCO2 and thus
maintaining [H+]a near its resting level. When [L]a increased further,
[H+]a increased. Sustainable running speeds (0.3-0.5 km x h-1 and below)
were often associated with increased VO2, VCO2, and [L]a in Iguana. Sixfold
increases in VCO2 and 9-mM increments in [L]a were accompanied by
sufficient increase in Veff (9-fold) to maintain [H+]a at or below its
control level. When [L]a increased further, [H+]a increased. These results
indicate that both lizard species maintain blood acid-base homeostasis
rather effectively via ventilatory adjustments at moderate exercise
intensities.
