'Blood-doping' effects on hematocrit regulation and oxygen consumption in late-stage chicken embryos (Gallus gallus)

The extent to which hematocrit (Hct) is regulated and the impact of altered Hct on blood oxygen transport in avian embryos are largely unknown. Consequently, we investigated how acute blood removal or Ringer solution injection modified Hct in day 15 embryos, and how ;blood doping' with erythrocyte-enriched whole blood influenced O(2) consumption in day 15-17 chicken embryos. Mean Hct (+/-s.e.m.) at day 15, 16 and 17 was 26.7+/-0.6%, 28.0+/-0.4% and 30.7+/-0.5%, respectively. Blood withdrawal (19 increments of 125 microl each, separated by 30 min) caused a progressive fall in Hct to approximately 12% at day 15. Hct decline was strictly proportional to the extent of blood withdrawal. Incremental Ringer solution injection over an 8 h period, transiently increasing blood volume up to 85% over initial values, did not decrease Hct, indicating that injected Ringer solution rapidly left the circulating blood compartment. Blood doping with erythrocyte-enriched whole blood artificially elevated Hct from 27% to 38%, but caused no significant change in routine O(2) consumption (0.35-0.39 ml O(2) min(-1) egg(-1)) at any point over the subsequent 6 h period in day 15-17 embryos. We conclude that Hct is not protected acutely in day 15 chicken embryos, with no evidence of erythrocyte sequestration or release. Additionally, at day 15-17, Hct increases of approximately 10% do not enhance embryonic oxygen consumption, suggesting that blood oxygen carrying capacity per se is not limiting to oxygen consumption.