Effects of temperature on acid-base balance and ventilation in desert iguanas

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Abstract
The effects of constant and changing temperatures on blood acid-base status and pulmonary ventilation were studied in the eurythermal lizard D. dorsalis. Constant temperatures between 18 and 42.degree. C maintained for 24 h or more produced arterial pH changes of -0.0145 U/degree C. Arterial CO2 tension (PCO2) increased from 9.9 to 32 Torr and plasma [HCO3-] and total CO2 contents remained constant at near 19 and 22 mM, respectively. Under constant temperature conditions, ventilation-gas exchange ratios (.ovrhdot.VE/.ovrhdot.MCO2 and .ovrhdot.VE/.ovrhdot.MO2) were inversely related to temperature and can adequately explain the changes in arterial PCO2 and pH. During warming and cooling between 25-42.degree. C arterial pH, PCO2, [HCO3-] and respiratory exchange ratios (.ovrhdot.MCO2/.ovrhdot.MO2) were similar to steady-state values. Warming and cooling each took about 2 h. During the temperature changes, rapid changes in lung ventilation following steady-state patterns were seen. Blood relative alkalinity changed slightly with steady-state or changing body temperatures, whereas calculated charge on protein histidine imidazole was closely conserved. Cooling to 17-18.degree. C resulted in a transient respiratory acidosis correlated with a decline in the ratio .ovrhdot.VE/.ovrhdot.MCO2. After 12-24 h at 17-18.degree. C, pH, PCO2 and .ovrhdot.VE returned to steady-state values. The importance of thermal history to patterns of acid-base regulation in reptiles is discussed.