CO₂ regulation in the toad, Bufo marinus marinus (L.)

Blood acid-base regulation of Bufo marinus marinus (L.) was examined in hydrated and dehydrated toads under normal and hypercapnic conditions. Serial samples of arterial blood were taken from free-moving unanaesthetized animals and analyzed for pH (pHa), PCO₂ (PaCO₂, torr) and HCO₃ (mM/1). When exposed to a 5% CO₂ gas mixture, the hydrated animal undergoes an initial respiratory acidosis which is progressively compensated for, over a 24-48 h period, by an increase in blood bicarbonate. Following return to air, arterial pH, PCO₂ and HCO₃ gradually reach normal values over a 2-4 day period. The same basic pattern of regulation was apparent in dehydrated animals although the initial acidosis was more pronounced and the subsequent return of the arterial blood to normal conditions did not occur. A CO₂ dissociation curve (PCO₂, torr vs. Total CO₂, mM/1) was prepared by equilibrating blood samples with known co₂ concentrations in tonometers. The CO₂ carrying capacity did not differ significantly (t .05) in the oxygenated or deoxygenated state of the haemoglobin molecule.