The Effects of Hypercapnia on the Arterial Acid-Base Status in the Tegu Lizard, Tupinambis Nigropunctatus

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Abstract
The effects of hypercapnia on the arterial acid-base status of the Tegu lizard, Tupinambis nigropunctatus (Spix), were studied at 25°C. Arterial PCOCO2 increased over the first 2 h of hypercapnia causing a fall in arterial plasma pH (pHa) of about 0.17 units with ≈4% CO2 and about 0.3 units with ≈7% CO2. In both conditions, plasma pH increased slightly (≈0.02units) between 2 and 72 h. Plasma [HCO3−] rose during the initial increase of PaCOCO2 (by approx. 5.5 mmol with ≈7% CO2; approx. 1.9 mmoll−1 with ≈4% CO2) during the first 2h, and further increased by 4 mmoll−1 between 2 and 72 h of hypercapnia, while PaCOCO2 did not change. The increases of plasma [HCO3−] resulted in a recovery of pH, by 38 or 32 % (≈4 and ≈7% CO2, respectively) relative to the fall of pH, that would occur at constant [HCO3−]. The limited and incomplete compensation of pHa during environmental hypercapnia is consistent with data for other air-breathing ectothermic vertebrates, and contrasts with the typical response of water-breathing fish, in which compensation is usually complete. Note: