Influence of the coronary circulation on thermal tolerance and cardiac performance during warming in rainbow trout.
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-1across 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-1in 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 tachycardia 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.
Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and andreas.ekstrom@bioenv.gu.se.
Andreas
A
Ekström
Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and.
Michael
M
Axelsson
Department of Animal Environment and Health, Swedish University of Agricultural Sciences, Skara, Sweden.
Albin
A
Gräns
Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and.
Jeroen
0000-0002-3671-5038
J
Brijs
Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden; and.
Erik
E
Sandblom
D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology*; D003326:Coronary Circulation / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D018869:Heat-Shock Response / Q000502:physiology*; D006358:Hot Temperature; D008297:Male; D017686:Oncorhynchus mykiss / Q000502:physiology*; D009929:Organ Size / Q000502:physiology; D012727:Sex Characteristics; D000071436:Thermotolerance / Q000502:physiology*
ECG; compact myocardium; coronary artery; coronary blood flow; coronary ligation; critical thermal maximum