'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.

Body, eye, and chorioallantoic vessel growth are not dependent on cardiac output level in day 3-4 chicken embryos.

Normal aerobic metabolic rates persist in the early chicken embryo after elimination of cardiac output, but the dependence of tissue growth and differentiation on blood flow is unknown in these early stages. We partially ligated (25-50% occlusion) the ventricular outflow tract of Hamburger-Hamilton stage (HH) 16-18 embryos, producing a wide range of cardiac output. For the next approximately 48 h (to HH 24), we measured heart rate (HR), stroke volume (SV), and cardiac output (CO), as well as these growth indicators: eye diameter, chorioallantoic vessel density, and body mass. Acutely, HR declined with partial ligation (from 108 to 98 beats/min). Paradoxically, SV and CO decreased sharply in most embryos but increased in others, collectively producing the desired large variation (up to 25-fold) in CO and permitting assessment of tissue growth over a very large range of blood perfusion. Eye diameter doubled (from 0.6 to 1.2 mm) with development from HH 16 to HH 24, but within a developmental cohort there was no significant correlation between eye diameter and CO over a 25-fold range of CO. Similarly, chorioallantoic membrane vessel index was independent of CO over the CO range at all stages. Finally, body mass increase during development was not significantly affected by partial conal truncal ligation. Collectively, these data suggest that normal eye and vessel growth and body mass accumulation occur independent of their rate of blood perfusion, supporting the hypothesis of prosynchronotropy-that the heart begins to beat and generate blood flow in advance of the actual need for convective blood flow to tissues.