Blood oxygen carriage in the marsupial, tammar wallaby (Macropus eugenii), at prenatal and neonatal stages.

The measurements reported here are the first to be made on oxygen carriage of a prenatal marsupial. The oxygen equilibrium curves (OECs) of tammar wallaby blood 1-2 days before the due date of birth showed a high P50 (mean = 44 Torr at 36 degrees C at a PCO2 of 34 Torr), more than 1.5 times that of the mother. This was confirmed by measurements in red cell suspensions at controlled pH. The finding of a higher P50 than in adult is in contrast to the general finding in eutherian (placental) mammals. Also they showed interaction between O2 and CO2 carriage (expressed as delta log P50/delta log PCO2 between 34 and 64 Torr PCO2) about half the magnitude of that in adults. At high PCO2 this effect reversed in the lower part but not in the upper part of the OEC. The Hill plot of the OECs showed a bend in the middle range of saturation: in nearly all cases the Hill coefficient (nH) was greater than 4.0 above about 50% saturation suggesting aggregation of haemoglobin tetramers. These results are similar to those previously reported for neonatal tammars and confirmed by further measurements in this study. The prenatals all had four haemoglobin types, identical with those found in the neonates.