The effect of exposure to increased carbon dioxide tensions on ammonium excretion by the urinary bladder of the toad Bufo marinus was studied. Ammonium excretion had been previously demonstrated in NH₄Cl-induced acidotic toads. No significant change in ammonium concentration was observed in four toads exposed to 1 (±0.05%) CO₂ for a 24 hour period. A significant increase in ammonium concentration was observed in 22 toads exposed to 5 (±0.05%) CO₂ for a 24 hour period. Ambient PCO₂ measurements ranged from a mean of 2.22 mm Hg in the control animals to 36.62 mm Hg in the toads under 5 per cent hypercapnic conditions. Results from this study indicate that Bufo marinus increases NH₄⁺ excretion in an attempt to buffer, to some extent, the decrease in blood pH caused by an increased carbon dioxide tension.
Gary Allison Vaughan (Thu,) studied this question.