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Hypoxic incubation at 50% of atmospheric levels shifts the cardiovascular response to acute hypoxia in American alligators, Alligator mississippiensis

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Abstract

We designed a series of studies to investigate whether hypoxia (10% O2) from 20% of incubation to hatching, or from 20 to 50% of incubation, affects cardiovascular function when juvenile American alligators reached an age of 4–5 years compared to juveniles that were incubated in 21% O2. At this age, we measured blood flows in all the major arteries as well as heart rate, blood pressure, and blood gases in animals in normoxia and acute hypoxia (10% O2 and 5% O2). In all three groups, exposure to acute hypoxia of 10% O2 caused a decrease in blood O2 concentration and an increase in heart rate in 4–5-year-old animals, with limited effects on blood flow in the major outflow vessels of the heart. In response to more acute hypoxia (5% O2), where blood O2 concentration decreased even further, we measured increased heart rate and blood flow in the right aorta, subclavian artery, carotid artery, and pulmonary artery; however, blood flow in the left aorta either decreased or did not change. Embryonic exposure to hypoxia increased the threshold for eliciting an increase in heart rate indicative of a decrease in sensitivity. Alligators that had been incubated in hypoxia also had higher arterial PCO2 values in normoxia, suggesting a reduction in ventilation relative to metabolism.

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Acknowledgements

We thank Tiffany Millar for her valuable aid in managing the alligators used in this study. We also thank Dr. William Joyce for his comments on the final manuscript. Finally, we thank Kaitlin Steiger for her aid in carrying out portions of the study. Funding for the project was provided to DAC II by the National Science Foundation IOS 1755187.

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Authors and Affiliations

  1. Department of Surgery, Center for Organogenesis and Trauma, University of Texas Southwestern, Dallas, TX, 75390, USA

    Janna L. Crossley

  2. Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX, 76203, USA

    Janna L. Crossley, Brandt Smith, Melissa Tull & Dane A. Crossley II

  3. Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA, 70643, USA

    Ruth M. Elsey

  4. Department of Biology, Zoophysiology, Aarhus University, Aarhus C, Denmark

    Tobias Wang

Authors
  1. Janna L. Crossley
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  2. Brandt Smith
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  4. Ruth M. Elsey
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  5. Tobias Wang
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  6. Dane A. Crossley II
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Contributions

All of the authors designed the experiments. JLC, DAC II, TL and MT conducted the studies. DAC II analyzed the data. JLC and DAC II drafted the manuscript, which was subsequently edited by all of the other authors. All of the authors approved the final version of the manuscript.

Corresponding author

Correspondence to Dane A. Crossley II.

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Communicated by P. Withers.

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Crossley, J.L., Smith, B., Tull, M. et al. Hypoxic incubation at 50% of atmospheric levels shifts the cardiovascular response to acute hypoxia in American alligators, Alligator mississippiensis. J Comp Physiol B 193, 545–556 (2023). https://doi.org/10.1007/s00360-023-01510-8

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