| 1. |
- Morgenroth, Daniel, et al.
(författare)
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Coronary blood flow influences tolerance to environmental extremes in fish.
- 2021
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Ingår i: The Journal of experimental biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 224:8
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Tidskriftsartikel (refereegranskat)abstract
- Approximately half of all fishes have, in addition to the luminal venous O2 supply, a coronary circulation supplying the heart with fully oxygenated blood. Yet, it is not fully understood how coronary O2 delivery affects tolerance to environmental extremes such as warming and hypoxia. Hypoxia reduces arterial oxygenation, while warming increases overall tissue O2 demand. Thus, as both stressors are associated with reduced venous O2 supply to the heart, we hypothesised that coronary flow benefits hypoxia and warming tolerance. To test this hypothesis, we blocked coronary blood flow (via surgical coronary ligation) in rainbow trout (Oncorhynchus mykiss), and assessed how in vivo cardiorespiratory performance and whole-animal tolerance to acute hypoxia and warming was affected. While coronary ligation reduced routine stroke volume relative to trout with intact coronaries, cardiac output was maintained by increases in heart rate. However, in hypoxia, coronary ligated trout were unable to increase stroke volume to maintain cardiac output when bradycardia developed, which was associated with a slightly reduced hypoxia tolerance. Moreover, during acute warming coronary ligation caused cardiac function to collapse at lower temperatures, and reduced overall heat tolerance relative to trout with intact coronaries. We also found a positive relationship between individual hypoxia and heat tolerance across treatment groups, and tolerance to both environmental stressors was positively correlated with cardiac performance. Collectively, our findings show that coronary perfusion improves cardiac O2 supply, and therefore, cardiovascular function at environmental extremes, which benefits tolerance to natural and anthropogenically induced environmental perturbations.
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| 2. |
- Ekström, Andreas, 1979, et al.
(författare)
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Adrenergic tone benefits cardiac performance and warming tolerance in two teleost fishes that lack a coronary circulation.
- 2021
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Ingår i: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology. - : Springer Science and Business Media LLC. - 1432-136X. ; 191, s. 701-9
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Tidskriftsartikel (refereegranskat)abstract
- Tolerance to acute environmental warming in fish is partly governed by the functional capacity of the heart to increase systemic oxygen delivery at high temperatures. However, cardiac function typically deteriorates at high temperatures, due to declining heart rate and an impaired capacity to maintain or increase cardiac stroke volume, which in turn has been attributed to a deterioration of the electrical conductivity of cardiac tissues and/or an impaired cardiac oxygen supply. While autonomic regulation of the heart may benefit cardiac function during warming by improving myocardial oxygenation, contractility and conductivity, the role of these processes for determining whole animal thermal tolerance is not clear. This is in part because interpretations of previous pharmacological in vivo experiments in salmonids are ambiguous and were confounded by potential compensatory increases in coronary oxygen delivery to the myocardium. Here, we tested the previously advanced hypothesis that cardiac autonomic control benefits heart function and acute warming tolerance in perch (Perca fluviatilis) and roach (Rutilus rutilus); two species that lack coronary arteries and rely entirely on luminal venous oxygen supplies for cardiac oxygenation. Pharmacological blockade of β-adrenergic tone lowered the upper temperature where heart rate started to decline in both species, marking the onset of cardiac failure, and reduced the critical thermal maximum (CTmax) in perch. Cholinergic (muscarinic) blockade had no effect on these thermal tolerance indices. Our findings are consistent with the hypothesis that adrenergic stimulation improves cardiac performance during acute warming, which, at least in perch, increases acute thermal tolerance.
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| 3. |
- Ekström, Andreas, 1979, et al.
(författare)
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Cardiorespiratory adjustments to chronic environmental warming improve hypoxia tolerance in European perch (Perca fluviatilis).
- 2021
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Ingår i: The Journal of experimental biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 224:6
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Tidskriftsartikel (refereegranskat)abstract
- Aquatic hypoxia will become increasingly prevalent in the future as a result of eutrophication combined with climate warming. While short-term warming typically constrains fish hypoxia tolerance, many fishes cope with warming by adjusting physiological traits through thermal acclimation. Yet, little is known about how such adjustments affect tolerance to hypoxia. We examined European perch (Perca fluviatilis) from the Biotest enclosure (23°C, Biotest population), a unique ∼1km2 ecosystem artificially warmed by cooling water from a nuclear power plant, and an adjacent reference site (16-18°C, reference population). Specifically, we evaluated how acute and chronic warming affect routine oxygen consumption rate (ṀO2,routine) and cardiovascular performance in acute hypoxia, alongside assessment of the thermal acclimation of the aerobic contribution to hypoxia tolerance (critical O2 tension for ṀO2,routine: Pcrit) and absolute hypoxia tolerance (O2 tension at loss of equilibrium; PLOE). Chronic adjustments (possibly across lifetime or generations) alleviated energetic costs of warming in Biotest perch by depressing ṀO2,routine and cardiac output, and by increasing blood O2 carrying capacity relative to reference perch acutely warmed to 23°C. These adjustments were associated with improved maintenance of cardiovascular function and ṀO2,routine in hypoxia (i.e. reduced Pcrit). However, while Pcrit was only partially thermally compensated in Biotest perch, they had superior absolute hypoxia tolerance (i.e. lowest PLOE) relative to reference perch irrespective of temperature. We show that European perch can thermally adjust physiological traits to safeguard and even improve hypoxia tolerance during chronic environmental warming. This points to cautious optimism that eurythermal fish species may be resilient to the imposition of impaired hypoxia tolerance with climate warming.
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| 4. |
- McArley, Tristan J., et al.
(författare)
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Normoxic limitation of maximal oxygen consumption rate, aerobic scope and cardiac performance in exhaustively exercised rainbow trout (Oncorhynchus mykiss)
- 2021
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 0022-0949 .- 1477-9145. ; 224:15
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Tidskriftsartikel (refereegranskat)abstract
- In fish, maximum O-2 consumption rate ((M) over dot(O2,max)) and aerobic scope can be expanded following exhaustive exercise in hyperoxia; however, the mechanisms explaining this are yet to be identified. Here, in exhaustively exercised rainbow trout (Oncorhynchus mykiss), we assessed the influence of hyperoxia on (M) over dot(O2,max), aerobic scope, cardiac function and blood parameters to address this knowledge gap. Relative to normoxia, (M) over dot(O2,max) was 33% higher under hyperoxia, and this drove a similar increase in aerobic scope. Cardiac output was significantly elevated under hyperoxia at (M) over dot(O2,max) because of increased stroke volume, indicating that hyperoxia released a constraint on cardiac contractility apparent with normoxia. Thus, hyperoxia improved maximal cardiac performance, thereby enhancing tissue O-2 delivery and allowing a higher (M) over dot(O2,max) Venous blood O-2 partial pressure (PvO(2)) was elevated in hyperoxia at (M) over dot(O2,max), suggesting a contribution of improved luminal O-2 supply in enhanced cardiac contractility. Additionally, despite reduced haemoglobin and higher PvO(2), hyperoxia treated fish retained a higher arterio-venous O-2 content difference at (M) over dot(O2,max). This may have been possible because of hyperoxia offsetting declines in arterial oxygenation that are known to occur following exhaustive exercise in normoxia. If this occurs, increased contractility at (M) over dot(O2,max) with hyperoxia may also relate to an improved O-2 supply to the compact myocardium via the coronary artery. Our findings show (M) over dot(O2,max) and aerobic scope may be limited in normoxia following exhaustive exercise as a result of constrained maximal cardiac performance and highlight the need to further examine whether or not exhaustive exercise protocols are suitable for eliciting (M) over dot(O2,max) and estimating aerobic scope in rainbow trout.
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| 5. |
- Sundell, Erika, et al.
(författare)
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Energetic savings and cardiovascular dynamics of a marine euryhaline fish (Myoxocephalus scorpius) in reduced salinity
- 2021
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Ingår i: Journal of Comparative Physiology B-Biochemical Systems and Environmental Physiology. - : Springer Science and Business Media LLC. - 0174-1578 .- 1432-136X. ; 191, s. 301-311
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Tidskriftsartikel (refereegranskat)abstract
- Few studies have addressed how reduced water salinity affects cardiovascular and metabolic function in marine euryhaline fishes, despite its relevance for predicting impacts of natural salinity variations and ongoing climate change on marine fish populations. Here, shorthorn sculpin (Myoxocephalus scorpius) were subjected to different durations of reduced water salinity from 33 to 15 ppt. Routine metabolic rate decreased after short-term acclimation (4-9 days) to 15 ppt, which corresponded with similar reductions in cardiac output. Likewise, standard metabolic rate decreased after acute transition (3 h) from 33 to 15 ppt, suggesting a reduced energetic cost of osmoregulation at 15 ppt. Interestingly, gut blood flow remained unchanged across salinities, which contrasts with previous findings in freshwater euryhaline teleosts (e.g., rainbow trout) exposed to different salinities. Although plasma osmolality, [Na+], [Cl-] and [Ca2+] decreased in 15 ppt, there were no signs of cellular osmotic stress as plasma [K+], [hemoglobin] and hematocrit remained unchanged. Taken together, our data suggest that shorthorn sculpin are relatively weak plasma osmoregulators that apply a strategy whereby epithelial ion transport mechanisms are partially maintained across salinities, while plasma composition is allowed to fluctuate within certain ranges. This may have energetic benefits in environments where salinity naturally fluctuates, and could provide shorthorn sculpin with competitive advantages if salinity fluctuations intensify with climate change in the future.
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| 6. |
- Twardek, W. M., et al.
(författare)
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Field assessments of heart rate dynamics during spawning migration of wild and hatchery-reared Chinook salmon
- 2021
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Ingår i: Philosophical Transactions of the Royal Society B-Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 376:1830
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Tidskriftsartikel (refereegranskat)abstract
- During spawning, adult Pacific salmonids (Oncorhynchus spp.) complete challenging upriver migrations during which energy and oxygen delivery must be partitioned into activities such as locomotion, maturation and spawning behaviours under the constraints of an individual's cardiac capacity. To advance our understanding of cardiac function in free-swimming fishes, we implanted migrating adult Chinook salmon (Oncorhynchus tshawytscha) collected near the mouth of the Sydenham River, Ontario, with heart rate (f(H)) biologgers that recorded f(H) every 3 min until these semelparous fish expired on spawning grounds several days later. Fundamental aspects of cardiac function were quantified, including resting, routine and maximum f(H), as well as scope for f(H) (maximum-resting f(H)). Predictors of f(H) were explored using generalized least-squares regression, including water temperature, discharge, fish size and fish origin (wild versus hatchery). Heart rate was positively correlated with water temperature, which aligned closely with daily and seasonal shifts. Wild fish had slower resting heart rates than hatchery fish, which led to significantly higher scope for f(H). Our findings suggest that wild salmon may have better cardiac capacity during migration than hatchery fish, potentially promoting migration success in wild fish. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.
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| 7. |
- Zena, Lucas, 1984, et al.
(författare)
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It takes time to heal a broken heart: ventricular plasticity improves heart performance after myocardial infarction in rainbow trout, Oncorhynchus mykiss
- 2021
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 0022-0949 .- 1477-9145. ; 224:23
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Tidskriftsartikel (refereegranskat)abstract
- Coronary arteriosclerosis is a common feature of both wild and farmed salmonid fishes and may be linked to stress-induced cardiac pathologies. Yet, the plasticity and capacity for long-term myocardial restructuring and recovery following a restriction in coronary blood supply are unknown. Here, we analyzed the consequences of acute (3 days) and chronic ( from 33 to 62 days) coronary occlusion (i.e. coronary artery ligation) on cardiac morphological characteristics and in vivo function in juvenile rainbow trout, Oncorhynchus mykiss. Acute coronary artery occlusion resulted in elevated resting heart rate and decreased inter-beat variability, which are both markers of autonomic dysfunction following acute myocardial ischemia, along with severely reduced heart rate scope (maximum-resting heart rate) relative to sham-operated trout. We also observed a loss of myocardial interstitial collagen and compact myocardium. Following long-term coronary artery ligation, resting heart rate and heart rate scope normalized relative to sham-operated trout. Moreover, a distinct fibrous collagen layer separating the compact myocardium into two layers had formed. This may contribute to maintain ventricular integrity across the cardiac cycle or, alternatively, demark a region of the compact myocardium that continues to receive oxygen from the luminal venous blood. Taken together, we demonstrate that rainbow trout may cope with the aversive effects caused by coronary artery obstruction through plastic ventricular remodeling, which, at least in part, restores cardiac performance and myocardium oxygenation.
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