Journal of Comparative Physiology B

, Volume 169, Issue 2, pp 85–92

Heart rate responses to altered ambient oxygen in early (days 3–9) chick embryos in the intact egg

  • R. Akiyama
  • H. Mitsubayashi
  • H. Tazawa
  • W. W. Burggren
ORIGINAL PAPER

Abstract

Normal heart rate (HR), and the HR responses to hypoxia and hyperoxia during early heart development in chick embyros have not been studied in detail, particularly in undisturbed embryos within the intact egg. HR was measured in day 3–9 chick embryos at 38 °C using relatively noninvasive impedance cardiography. Embryos were exposed to air (control) and to hypoxic (10% O2) or hyperoxic (100% O2) gas for a 2-h or 4-h period, during which HR was continually monitored. Control (normoxic) HR increased from about 150 beats per min (bpm) on day 3 to about 240 bpm on days 7–9. HR in very early embryos showed a variety of moderate responses to hypoxia (all survived), but as development progressed beyond day 6, hypoxic exposure induced a profound bradycardia that frequently terminated in death before the end of the measurement period. In contrast to the marked developmental changes in hypoxic sensitivity, HR showed little response to hyperoxia throughout development, suggesting no “hypoxic drive” to HR. We speculate that hypoxia has little effect early in development because of the embryo's small absolute O2 demand, but as the embryo grows, hypoxia represents a progressively more severe perturbation. Although general trends were identified, there was considerable variation in both HR and HR responses to ambient O2 changes between individuals of the same developmental stage.

Key words Early chick embryos Heart rate/heart rate responses Hypoxia/hyperoxia Development Bradycardia 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1999

Authors and Affiliations

  • R. Akiyama
    • 1
  • H. Mitsubayashi
    • 1
  • H. Tazawa
    • 1
  • W. W. Burggren
    • 2
  1. 1.Department of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan e-mail: tazawa@oyna.cc.muroran-it.ac.jp, Fax: +81-143-46-5501JP
  2. 2.Department of Biological Sciences, University of North Texas, Denton, Texas 76205-5220, USAUS

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