Acid-base balance during lactic acid infusion in the lizard Varanus salvator

Although reptiles rely heavily on anaerobic metabolism and lactic acid production during activity, little is known concerning their ventilatory response to the attendant metabolic acidosis. We measured arterial PCO2, H+ and lactate (L)ion concentrations, and the rates of CO2 (MCO2) and O2 (MO2) exchange in Varanus salvator (n = 9) during intravenous infusions of lactic acid (HL) or sodium lactate (NaL; 250 mM) at rest. Two protocols were used: (1) 15 min infusions of 0.42 ml/min at both 25 and 35 degrees C with measurements every 5 min; (2) 4.5 min infusions of 1.73 ml/min at 35 degrees C with measurements at 4.5 min. At 35 degrees C, control pH decreased from its value at 25 degrees C with a slope of -0.007/degrees C and PaCO2 increased. The results of HL infusion were: (1) [L]a increased, (2) MCO2 increased, (3) R (MCO2/MO2) increased, (4) pHa decreased, and (5) PaCO2 remained unchanged from control at both temperatures and at both infusion rates. The only significant changes in PaCO2 observed were following the termination of fast HL infusions, when PaCO2 decreased. In NaL infusions, only small changes were observed except in [L]a. The results indicate that: (1) delta pH/delta T in V. salvator is less than in other poikilothermic vertebrates, but consistent with other varanid lizards, (2) respiratory compensation is slight in response to acute metabolic acidosis in this species, and (3) ventilation follows changes in MCO2 rather closely, accounting for precise regulation of PaCO2 despite 4-fold increases in MCO2 elicited by bicarbonate buffering and increased metabolic rate.