title: Respiratory plasticity in response to changes in oxygen supply and demand.
abstract: Aerobic organisms maintain O(2) homeostasis by responding to changes in O(2) supply and demand in both short and long time domains. In this review, we introduce several specific examples of respiratory plasticity induced by chronic changes in O(2) supply (environmental hypoxia or hyperoxia) and demand (exercise-induced and temperature-induced changes in aerobic metabolism). These studies reveal that plasticity occurs throughout the respiratory system, including modifications to the gas exchanger, respiratory pigments, respiratory muscles, and the neural control systems responsible for ventilating the gas exchanger. While some of these responses appear appropriate (e.g., increases in lung surface area, blood O(2) capacity, and pulmonary ventilation in hypoxia), other responses are potentially harmful (e.g., increased muscle fatigability). Thus, it may be difficult to predict whole-animal performance based on the plasticity of a single system. Moreover, plastic responses may differ quantitatively and qualitatively at different developmental stages. Much of the current research in this field is focused on identifying the cellular and molecular mechanisms underlying respiratory plasticity. These studies suggest that a few key molecules, such as hypoxia inducible factor (HIF) and erythropoietin, may be involved in the expression of diverse forms of plasticity within and across species. Studying the various ways in which animals respond to respiratory challenges will enable a better understanding of the integrative response to chronic changes in O(2) supply and demand.
authors.affiliation: *Department of Biology, Bates College, Lewiston, ME 04240, USA; Department of Medicine, University of California, San Diego, CA, USA; White Mountain Research Station, University of California, San Diego, CA, USA; Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, St. Stephen's Green, Dublin 2, Ireland; Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Unit for Sports and Exercise Medicine, Institute of Clinical Medicine, University of Helsinki, Helsinki, Paasikivenkatu 4 00250, Finland; Institute of Veterinary Physiology, Vetsuisse Faculty, and Zurich Center for Integrative Human Physiology, University of Zurich, Winterthurerstrasse 260, CH-8057 Zurich, Switzerland; **Institut für Zoophysiologie, Universität Münster, Germany; Harvard Medical School, Brigham and Women's Hospital, 221 Longwood Avenue, Boston, MA 02115, USA; UCD School of Medicine and Medical Science, University College Dublin, Dublin, Ireland; Centre for the Neurobiology of Stress, Department of Life Sciences, University of Toronto, Scarborough; Department of Biology of Physical Activity, Faculty of Sport and Health Sciences, University of Jyväskylä, PO Box 35, 40014 Jyväskylä, Finland.
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