Cardio-respiratory ontogeny during chronic carbon monoxide exposure in the clawed frog Xenopus laevis

The present study investigates the ontogeny of cardio-respiratory physiology in Xenopus laevis where O2 transport is obstructed. Animals were raised from eggs (NF stage 1) to metamorphic climax (NF stage 63), while maintained either in air or in chronic 2 kPa CO, which functionally ablates O2 transport by hemoglobin (Hb). Whole-animal rate of oxygen consumption (.MO2), whole-body lactate concentration, individual mass, heart rate (fh) and stroke volume (Vs) were measured. Additionally, cardiac output (.Q) and the ratio of the rate of oxygen consumption to the total rate at which oxygen is transported in the blood (.MO2/.QO2) were calculated to determine limitations imparted when O2 transport is impaired. Our data on early development suggest that the onset of convective blood flow occurs prior to the absolute need for convection to supplement diffusive transport. Values for .MO2, whole-body lactate concentration, mass and fh did not differ significantly between controls and CO-exposed animals. However, CO-exposed animals showed a significant (P<0.05) increase in Vs, .MO2/.QO2 and .Q compared with controls. These results indicate that limiting blood O2 transport is not deleterious to metabolism and development as a whole and that convective oxygen transport via Hb is not essential for normal cardiovascular or respiratory function during larval development.