Respiratory adaptations in selected amphibians

Abstract

In order to evaluate some of the respiratory adaptations concomitant with the transition from water breathing to air breathing, three amphibians were studied: the aquatic Necturus maculosus which possesses external gills and a poorly developed lung, Amphiuma tridactylum which has no gills but remains in water and depends on pulmonary breathing, and the bullfrog, Rana catesbeiana, which is somewhat terrestrial and uses pulmonary respiration. Respectively for Necturus, Amphiuma and bullfrog the oxygen capacity was 6.3, 7.6, and 8.0 vol %; the affinity for 02 or P 50 at the physiological P CO 2 , was 14.5, 27 and 39 mm Hg; the Bohr effect or Δlog P 50/ΔpH was −0.131, −0.205 and −0.288; the CO 2 combining power at the physiological P CO 2 was 20.0, 31.2 and 30.4 vol % and the buffering capacity, or ΔHCO 3 −/ΔpH, was −8.0, −9.2, and −16.4 mM/1/pH. The respiratory characteristics of these animals kept at 20°C was studied by in vivo blood gas measurements made at the same temperature. Pa CO 2 and Pa CO 2 of Necturus kept in water were 35 and 4.4 mm Hg respectively. When removed from water the exchange of blood gases was greatly impaired in spite of frequent air breathing. In free-breathing Amphiuma Pa O 2 was 81 and Pa CO 2 6 mm Hg. When prevented from air breathing P O 2 decreased and P CO 2 increased slowly suggesting that the animal uses its skin to exchange gases with water fairly effectively. In the bullfrog Pa O 2 was 95 and Pa CO 2 8 mm Hg. When the animal was immersed, P O 2 decreased and P CO 2 increased rapidly suggesting the absence of efficient skin respiration. These findings are regarded as expressing adaptive changes to meet an increased O 2 availability of the external medium, and on elevated internal P CO 2 in the transition from aquatic to aerial respiration.