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Influence of the coronary circulation on thermal tolerance and cardiac performance during warming in rainbow trout

Journal article
Authors Andreas Ekström
Michael Axelsson
Albin Gräns
Jeroen Brijs
Erik Sandblom
Published in American Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume 312
Issue 4
Pages R549-R558
ISSN 0363-6119
Publication year 2017
Published at Department of Biological and Environmental Sciences
Pages R549-R558
Language en
Links https://doi.org/10.1152/ajpregu.005...
Keywords Compact myocardium, Coronary artery, Coronary blood flow, Coronary ligation, Critical thermal maximum, ECG
Subject categories Animal physiology

Abstract

© 2017 the American Physiological Society. Thermal tolerance in fish may be related to an oxygen limitation of cardiac function. While the hearts of some fish species receive oxygenated blood via a coronary circulation, the influence of this oxygen supply on thermal tolerance and cardiac performance during warming remain unexplored. Here, we analyzed the effect in vivo of acute warming on coronary blood flow in adult sexually mature rainbow trout (Onchorhynchus mykiss) and the consequences of chronic coronary ligation on cardiac function and thermal tolerance in juvenile trout. Coronary blood flow at 10°C was higher in females than males (0.56 ± 0.08 vs. 0.30 ± 0.08 ml·min -1 ·g ventricle -1 ), and averaged 0.47 ± 0.07 ml·min -1 ·g ventricle -1 across sexes. Warming increased coronary flow in both sexes until 14°C, at which it peaked and plateaued at 0.78 ± 0.1 and 0.61 ± 0.1 ml·min -1 ·g ventricle -1 in females and males, respectively. Thus, the scope for increasing coronary flow was 101% in males, but only 39% in females. Coronary-ligated juvenile trout exhibited elevated heart rate across temperatures, reduced Arrhenius breakpoint temperature for heart rate (23.0 vs. 24.6°C), and reduced upper critical thermal maximum (25.3 vs. 26.3°C). To further analyze the effects of coronary flow restriction on cardiac rhythmicity, electrocardiogram characteristics were determined before and after coronary occlusion in anesthetized trout. Occlusion resulted in reduced R-wave amplitude and an elevated S-T segment, indicating myocardial ischemia, while heart rate was unaffected. This suggests that the tachy cardia in ligated trout across temperatures in vivo was mainly to compensate for reduced cardiac contractility to maintain cardiac output. Moreover, our findings show that coronary flow increases with warming in a sex-specific manner. This may improve whole animal thermal tolerance, presumably by sustaining cardiac oxygenation and contractility at high temperatures.

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