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Blood Oxygenation and Cardiorespiratory Function in Steelhead Trout Oncorhynchus mykiss Challenged with an Acute Temperature Increase and Zatebradine-Induced Bradycardia

Blood Oxygenation and Cardiorespiratory Function in Steelhead Trout Oncorhynchus mykiss Challenged with an Acute Temperature Increase and Zatebradine-Induced Bradycardia

Journal of Thermal Biology 37(3): 0-210

To explore whether temperature-dependent increases in cardiac output (Q) are mediated solely through heart rate (fH) in fish to ensure adequate/efficient blood oxygenation, we injected steelhead trout with saline (control) or zatebradine hydrochloride (1. mg kg), and measured blood oxygen status, cardiorespiratory variables and cardiorespiratory synchrony during a critical thermal maximum (CTMax) test. The increasing temperature regimen itself (from 12 C to CTMax) resulted in large decreases in arterial oxygen partial pressure (PaO2) and content (CaO2)(by~35 and 25%, respectively). Further, there was little evidence of cardiorespiratory synchrony at 12 C, and the number of fish that showed synchrony at high temperatures only increased marginally (to 3 out of 7) despite the large decrease in PaO2. These results: (1) indicate that in some situations (e.g. when ventilation is exclusively/predominantly dependent on buccal-opercular pumping) the upper thermal tolerance of fish may be constrained by both cardiovascular and ventilatory performance; and question the importance of cardiorespiratory synchrony (ventilation-perfusion matching) for gas exchange in salmonids, and fishes, in general.Zatebradine injection decreased heart rate (fH) at 12 C by 11% and limited maximumfHto 78.6 5.9 vs. 116.5 5.7 beats minin controls. However, it did not affect maximum cardiac output (due to a compensatory increase inSV), ventilation, cardiorespiratory synchrony or PaO2. In contrast, metabolic scope and CTMaxwere lower in the zatebradine vs. control group [184.5 17.4 vs. 135.7 21.5 ml kgh(p<.5) and 23.7 .2 vs. 22.6 .4 C (p<.8), respectively]. This result was unrelated to maximumfHor scope forfH, and occurred despite higher values for blood oxygen content and haematocrit at>18 C in the zatebradine-treated fish. These latter findings suggest that zatebradine has non-pacemaker effects that limit tissue oxygen utilization and its usefulness forin vivostudies.

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Accession: 036331059

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DOI: 10.1016/j.jtherbio.2012.01.002

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