Blood O2 transport and Hb types in the embryonic Tammar Wallaby (Marsupialia, Macropus eugenii).

Blood oxygen transport and hemoglobin type have been studied in the developing Tammar Wallaby from 20 days gestation, just after the circulation first forms, until 28 days gestation, 2 days after birth. The oxygen equilibrium curves (OECs) of the embryonic whole blood had high P50 values, mean being 44.6 mmHg at 36 degrees C, PCO2 = 40 mmHg. In contrast to other viviparous species studied, the embryonic OECs were well to the right of the maternal OEC. There was no significant change in P50 throughout the age range studied. The curves had high Hill coefficients above about 50% saturation (mean = 5.65), indicating cooperativity between hemoglobin tetramers. The Bohr effect (measured as delta log P50/delta log PCO2) was low, about half that of the adult. The early embryos (days 20 and 21) had only 2 or 3 Hb types, with the other embryonic Hbs appearing by 22 days of gestation. The proportion of the four embryonic Hbs changed during development although one type was always predominant (> 45%). This is the first serial study of blood O2 carriage and Hb type in developing marsupial embryos. The finding of a right-shifted embryonic OEC throughout intrauterine development suggests that, contrary to current belief, a right-shifted curve may be physiologically advantageous to a developing embryo.