The ontogeny of cardio-respiratory function under chronically altered gas compositions in Xenopus laevis

The importance of diffusion and perfusion in terms of oxygen transport was evaluated by chronically altering environmental O-2 availability (hypoxia or hyperoxia) and blood O-2 content (carbon monoxide) through development in Xenopus Inevis. Oxygen consumption ((M) over dot(O2)), individual wet mass, heart rate (fH), and stroke volume (SV) were measured in animals raised from eggs to pre-metamorphic climax while maintained at 11, 21 and 35 kPa O-2, combined with and without 2 kPa carbon monoxide. Additionally, cardiac output ((Q) over dot), and a recently defined O-2 consumption/transport quotient ((M) over dot(O2).(Q) over dot(O2)(-1)) were calculated. Wet mass, (M) over dot(O2), and fH, were not significantly different between controls and experimental treatments at any developmental stage. However, with hemoglobin oxygen transport blocked by carbon monoxide, the exposed larvae showed an increased SV, (Q) over dot and (M) over dot(O2).(Q) over dot(O2)(-1). Combined, these data suggest that in spite of impaired blood O-2 convection, normal aerobic metabolism was maintained, indicating that direct diffusion of O-2 plays an important role in supplying oxygen during early development. (C) 1998 Elsevier Science B.V. All rights reserved.