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First published online December 15, 2004
Journal of Experimental Biology 208, 31-39 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01355

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Cardiovascular development in embryos of the American alligator Alligator mississippiensis: effects of chronic and acute hypoxia

Dane A. Crossley, II^1,* and Jordi Altimiras²

¹ Department of Ecology and Evolutionary Biology, University of California Irvine, Irvine, CA 92697, USA
² Department of Biology, IFM, Linköpings universitet, SE-58183 Linköping Sweden

^* Author for correspondence at present address: Oregon Health and Science University, Department of Physiology and Pharmacology/L334, 3181 SW Sam Jackson Park Road, Portland, OR 97201-3098, USA (e-mail: dcrossle{at}uci.edu)

Accepted 22 October 2004

Chronic hypoxic incubation is a common tool used to address the plasticity of morphological and physiological characteristics during vertebrate development. In this study chronic hypoxic incubation of embryonic American alligators resulted in both morphological (mass) and physiological changes. During normoxic incubation embryonic mass, liver mass and heart mass increased throughout the period of study, while yolk mass fell. Chronic hypoxia (10%O₂) resulted in a reduced embryonic mass at 80% and 90% of incubation. This reduction in embryonic mass was accompanied by a relative enlargement of the heart at 80% and 90% of incubation, while relative embryonic liver mass was similar to the normoxic group. Normoxic incubated alligators maintained a constant heart rate during the period of study, while mean arterial pressure rose continuously. Both levels of hypoxic incubation (15% and 10%O₂) resulted in a lower mean arterial pressure at 90% of incubation, while heart rate was lower in the 10%O₂ group only. Acute (5 min) exposure to 10%O₂ in the normoxic group resulted in a biphasic response, with a normotensive bradycardia occurring during the period of exposure and a hypertensive tachycardic response occurring during recovery. The embryos incubated under hypoxia also showed a blunted response to acute hypoxic stress. In conclusion, the main responses elicited by chronic hypoxic incubation, namely, cardiac enlargement, blunted hypoxic response and systemic vasodilation, may provide chronically hypoxic embryos with a new physiological repertoire for responding to hypoxia.

Key words: cardiovascular, embryonic, American alligator, Alligator mississippiensis, development, hypoxia.

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