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

Abstract

ABSTRACT The effects of hypercapnia on the arterial acid-base status of the Tegu lizard, Tupinambis nigropunctatus (Spix), were studied at 25 °C. Arterial 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 (≈ 0·02 units) between 2 and 72 h. Plasma [HCO3−] rose during the initial increase of (by approx. 5·5 mmol l−1 with ≈7 % CO2; approx. 1·9 mmol l−1 with ≈4% CO2) during the first 2h, and further increased by 4 mmol I-1 between 2 and 72 h of hypercapnia, while 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 pHa 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.