Oxygen affinity and equilibrium curve shape in blood of chicken embryos

Abstract

Oxygen equilibrium curves of blood from 4- to 18-day chicken embryos were investigated at 38°C. Curves were recorded at the P CO 2 measured in the air cell of each egg. Since arterial P CO 2 is known to closely approximate that of the air cell, these curves reflect in vitro arterial pH. Curves were also recorded at a second, higher P CO 2 , allowig calculation of he curve at estimated venous P CO 2 and of physiological curves by interpolation. Half saturation P O 2 of physiological curves increased from 38 Torr at 4 days to 52 Torr at 8 days, and then decreased to 31 Torr at 198 days. Increasing blood oxygen affinity late in development favors oxygen loading at the falling P O 2 that exists at the chorioallantoic surface, while higher affinity before 8 days may be related to diffussion resistance of the inner shell membrane early in incubation. In blood from 4- to 6-day embryos, the Hill coefficient, n H, of curves at air cell P CO 2 increased from 1.5 at oxygen saturation 0.1 to 6.5 at saturation 0.85. After 6 days, n H steadily increased at low saturation and decreased at high saturation. By 18 days, n H varied only from 2 to 3.4. A biphasic equilibrium curve shape (hump at the low end of the oxygen equilibrium curve) developed in 4- and 5-day embryo blood after a period of storage on ice, and was accentuated if some of the cells were intentionally lysed.