Papers by Andreas Ekström
Journal of Experimental Biology
Salmonid ventricles are composed of spongy and compact myocardium, the latter being perfused via ... more Salmonid ventricles are composed of spongy and compact myocardium, the latter being perfused via a coronary circulation. Rainbow trout (Oncorhynchus mykiss) acclimated to sea water have higher proportions of compact myocardium and display stroke volume-mediated elevations in resting cardiac output relative to freshwater-acclimated trout, probably to meet the higher metabolic needs of osmoregulatory functions. Here, we tested the hypothesis that cardiorespiratory performance of rainbow trout in sea water is more dependent on coronary perfusion by assessing the effects of coronary ligation on cardiorespiratory function in resting and exhaustively exercised trout acclimated to fresh water or sea water. While ligation only had minor effects on resting cardiorespiratory function across salinities, cardiac function after chasing to exhaustion was impaired, presumably as a consequence of atrioventricular block. Ligation reduced maximum O2 consumption rate by 33% and 17% in fish acclimated ...
Proceedings of the Royal Society B: Biological Sciences
Recent evidence has suggested environmental hyperoxia (O 2 supersaturation) can boost cardiorespi... more Recent evidence has suggested environmental hyperoxia (O 2 supersaturation) can boost cardiorespiratory performance in aquatic ectotherms, thereby increasing resilience to extreme heat waves associated with climate change. Here, using rainbow trout ( Oncorhynchus mykiss ) as a model species, we analysed whether improved cardiorespiratory performance can explain the increased thermal tolerance of fish in hyperoxia (200% air saturation). Moreover, we collated available literature data to assess the prevalence and magnitude of hyperoxia-induced thermal tolerance across fish species. During acute warming, O 2 consumption rate was substantially elevated under hyperoxia relative to normoxia beyond 23°C. This was partly driven by higher cardiac output resulting from improved cardiac contractility. Notably, hyperoxia mitigated the rise in plasma lactate at temperatures approaching upper limits and elevated the critical thermal maximum (+0.87°C). Together, these findings show, at least in ra...
Journal of Comparative Physiology B, 2021
Tolerance to acute environmental warming in fish is partly governed by the functional capacity of... more 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 tha...
Nitric oxide (NO) is an important chemical factor that controls vascular tone in the cardiovascul... more Nitric oxide (NO) is an important chemical factor that controls vascular tone in the cardiovascular system. NO is a vasodilatory molecule that plays a role in blood pressure and blood flow regulation as well as vessel formation and tissue cell proliferation. NO influences the flow by which nutrients and other metabolites required for growth are transported to the tissues. The aim of this study was to investigate if NO, through mediation by the NO donors Sodium Nitroprusside (SNP) and S-Nitrosoglutathione (GSNO) affect growth and oxygen consumption of prenatal broiler chicken. The results indicate that, although the treatments did not have clear significant effects on the embryos or the organs examined, a slight delay in development can be observed in the GSNO treatment embryos. The study could not conclude, however, if this was due to effects of NO donors
Journal of Experimental Biology, 2021
Coronary arteriosclerosis is a common feature of both wild and farmed salmonid fishes and may be ... more 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...
Journal of Comparative Physiology B, 2021
When in seawater, rainbow trout (Oncorhynchus mykiss) drink to avoid dehydration and display stro... more When in seawater, rainbow trout (Oncorhynchus mykiss) drink to avoid dehydration and display stroke volume (SV) mediated elevations in cardiac output (CO) and an increased proportion of CO is diverted to the gastrointestinal tract as compared to when in freshwater. These cardiovascular alterations are associated with distinct reductions in systemic and gastrointestinal vascular resistance (RSys and RGI, respectively). Although increased gastrointestinal blood flow (GBF) is likely essential for osmoregulation in seawater, the sensory functions and mechanisms driving the vascular resistance changes and other associated cardiovascular changes in euryhaline fishes remain poorly understood. Here, we examined whether internal gastrointestinal mechanisms responsive to osmotic changes mediate the cardiovascular changes typically observed in seawater, by comparing the cardiovascular responses of freshwater-acclimated rainbow trout receiving continuous (for 4 days) gastric perfusion with half...
Journal of Comparative Physiology B, 2021
Few studies have addressed how reduced water salinity affects cardiovascular and metabolic functi... more 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 o...
Scientific Reports, 2020
Mitochondria are playing key roles in setting the thermal limits of fish, but how these organelle... more Mitochondria are playing key roles in setting the thermal limits of fish, but how these organelles participate in selection mechanisms during extreme thermal events associated with climate warming in natural populations is unclear. Here, we investigated the thermal effects on mitochondrial metabolism, oxidative stress, and mitochondrial gene expression in cardiac tissues of European perch (Perca fluviatilis) collected from an artificially heated ecosystem, the “Biotest enclosure”, and an adjacent reference area in the Baltic sea with normal temperatures (~ 23 °C and ~ 16 °C, respectively, at the time of capture in summer). Fish were sampled one month after a heat wave that caused the Biotest temperatures to peak at ~ 31.5 °C, causing significant mortality. When assayed at 23 °C, Biotest perch maintained high mitochondrial capacities, while reference perch displayed depressed mitochondrial functions relative to measurements at 16 °C. Moreover, mitochondrial gene expression of nd4 (mi...
Aquaculture, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Scientific Reports, 2020
Bio-logging devices can provide unique insights on the life of freely moving animals. However, im... more Bio-logging devices can provide unique insights on the life of freely moving animals. However, implanting these devices often requires invasive surgery that causes stress and physiological side-effects. While certain medications in connection to surgeries have therapeutic capacity, others may have aversive effects. Here, we hypothesized that the commonly prescribed prophylactic treatment with enrofloxacin would increase the physiological recovery rate and reduce the presence of systemic inflammation following the intraperitoneal implantation of a heart rate bio-logger in rainbow trout (Oncorhynchus mykiss). To assess post-surgical recovery, heart rate was recorded for 21 days in trout with or without enrofloxacin treatment. Contrary to our hypothesis, treated trout exhibited a prolonged recovery time and elevated resting heart rates during the first week of post-surgical recovery compared to untreated trout. In addition, an upregulated mRNA expression of TNFα in treated trout indica...
Scientific Reports, 2019
Some evidence suggests that cardiac mitochondrial functions might be involved in the resilience o... more Some evidence suggests that cardiac mitochondrial functions might be involved in the resilience of ectotherms such as fish to environmental warming. Here, we investigated the effects of acute and chronic changes in thermal regimes on cardiac mitochondrial plasticity and thermal sensitivity in perch (Perca fluviatilis) from an artificially heated ecosystem; the “Biotest enclosure” (~25 °C), and from an adjacent area in the Baltic Sea with normal temperatures (reference, ~16 °C). We evaluated cardiac mitochondrial respiration at assay temperatures of 16 and 25 °C, as well as activities of lactate dehydrogenase (LDH) and citrate synthase (CS) in Biotest and reference perch following 8 months laboratory-acclimation to either 16 or 25 °C. While both populations exhibited higher acute mitochondrial thermal sensitivity when acclimated to their natural habitat temperatures, this sensitivity was lost when Biotest and reference fish were acclimated to 16 and 25 °C, respectively. Moreover, ref...
Journal of Comparative Physiology B, 2019
Coronary perfusion and cardiac autonomic regulation may benefit myocardial oxygen delivery and th... more Coronary perfusion and cardiac autonomic regulation may benefit myocardial oxygen delivery and thermal performance of the teleost heart, and thus influence whole animal heat tolerance. Yet, no study has examined how coronary perfusion affects cardiac output during warming in vivo. Moreover, while β-adrenergic stimulation could protect cardiac contractility, and cholinergic decrease in heart rate may enhance myocardial oxygen diffusion at critically high temperatures, previous studies in rainbow trout (Oncorhynchus mykiss) using pharmacological antagonists to block cholinergic and β-adrenergic regulation showed contradictory results with regard to cardiac performance and heat tolerance. This could reflect intra-specific differences in the extent to which altered coronary perfusion buffered potential negative effects of the pharmacological blockade. Here, we first tested how cardiac performance and the critical thermal maximum (CTmax) were affected following a coronary ligation. We th...
Fisheries Management and Ecology, 2019
Socially induced stress and behavioural inhibition in response to angling exposure in rainbow tro... more Socially induced stress and behavioural inhibition in response to angling exposure in rainbow trout. Fisheries Management and Ecology, 26(6), pp. 611-620. There may be differences between this version and the published version. You are advised to consult the publisher's version if you wish to cite from it.
Biology Letters, 2018
Cardiac oxygenation is achieved via both coronary arterial and luminal venous oxygen supply route... more Cardiac oxygenation is achieved via both coronary arterial and luminal venous oxygen supply routes in many fish species. However, the relative importance of these supplies for cardiac and aerobic metabolic performance is not fully understood. Here, we investigated how coronary artery ligation in rainbow trout (Oncorhynchus mykiss), implanted with heart rate loggers, affected cardiorespiratory performancein vivo. While coronary ligation significantly elevated resting heart rate, the standard metabolic rate was unchanged compared to sham-treated controls. However, coronary ligation reduced the maximum metabolic rate while heart rate remained unchanged following enforced exercise. Thus, coronary ligation reduced metabolic and heart rate scopes by 29% and 74%, respectively. Our findings highlight the importance of coronary oxygen supply for overall cardiorespiratory performance in salmonid fish, and suggest that pathological conditions that impair coronary flow (e.g. coronary arterioscl...
Conservation Physiology, 2018
Greater salinity variations resulting from ongoing climate change requires consideration in conse... more Greater salinity variations resulting from ongoing climate change requires consideration in conservation management as this may impact on the performance of aquatic organisms. Euryhaline fish exhibit osmoregulatory flexibility and can exploit a wide range of salinities. In seawater (SW), they drink and absorb water in the intestine, which is associated with increased gastrointestinal blood flow. Yet, detailed information on other cardiovascular changes and their control across salinities is scant. Such knowledge is fundamental to understand how fish are affected during migrations between environments with different salinities, as well as by increased future salinity variability. We used rainbow trout (Oncorhynchus mykiss) as a euryhaline model species and determined dorsal aortic blood pressure, cardiac output and systemic vascular resistance in vivo after chronic freshwater-or SW-acclimation. We also assessed α-adrenergic control of blood pressure using pharmacological tools. Dorsal aortic blood pressure and systemic vascular resistance were reduced, whereas cardiac output increased in SW. α-Adrenergic stimulation with phenylephrine caused similar dose-dependent increases in resistance and pressure across salinities, indicating unaltered α-adrenoceptor sensitivity. α-Adrenergic blockade with prazosin decreased resistance and pressure across salinities, but the absolute reduction in resistance was smaller in SW. Yet, both pressure and resistance after prazosin remained consistently lower in SW. This shows that SW-acclimation lowers systemic resistance through reduced vascular α-adrenergic tone, along with other unknown vasodilating factors. The marked changes in adrenergic regulation of the vasculature across salinities discovered here may have implications for cardiovascular and aerobic performance of fishes, with possible impacts on fitnessrelated traits like digestion and exercise capacity. Moreover, the evolution of more complex circulatory control systems in teleost fishes compared with elasmobranchs and cyclostomes may have been an important factor in the evolution of euryhalinity, and may provide euryhaline teleosts with competitive advantages in more variable salinity environments of the future.
Journal of Experimental Biology, 2017
Although the mitochondrial metabolism responses to warm acclimation have been widely studied in f... more Although the mitochondrial metabolism responses to warm acclimation have been widely studied in fish, the time course of this process is less understood. Here, we characterise changes of rainbow trout (Oncorhyncus mykiss) cardiac mitochondrial metabolism during acute warming from 10 to 16°C, and during the subsequent warm acclimation for 39 days (D). We repeatedly measured mitochondrial O2 consumption in cardiac permeabilized fibers and functional integrity of mitochondria (i.e. mitochondrial coupling and cytochrome c effect) at two assay temperatures (10 and 16°C), as well as citrate synthase (CS) and lactate dehydrogenase (LDH) activities at room temperature. LDH and CS activities significantly increased between D0 (10°C acclimated fish) and D1 (acute warming to 16°C), while mitochondrial O2 consumption measured at respective in vivo temperatures did not change. Enzymatic activities and mitochondrial O2 consumption rates significantly decreased by D2, and remained stable during wa...
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2017
Thermal tolerance in fish may be related to an oxygen limitation of cardiac function. While the h... more 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-li...
Journal of Experimental Biology, 2016
Cellular and mitochondrial metabolic capacity of the heart has been suggested to limit performanc... more Cellular and mitochondrial metabolic capacity of the heart has been suggested to limit performance of fish at warm temperatures. We investigated this hypothesis by studying the effects of acute temperature increases (16, 23, 30, 32.5 and 36°C) on the thermal sensitivity of 10 key enzymes governing cardiac oxidative and glycolytic metabolism in two populations of European perch (Perca fluviatilis) field-acclimated to 15.5 and 22.5°C, as well as the effects of acclimation on cardiac lipid composition. In both populations of perch, the activity of glycolytic (pyruvate kinase and lactate dehydrogenase) and tricarboxylic acid cycle (pyruvate dehydrogenase and citrate synthase) enzymes increased with acute warming. However, at temperatures exceeding 30°C, a drastic thermally-induced decline in citrate synthase activity was observed in the cold- and warm-acclimated populations respectively, indicating a bottleneck for producing the reducing equivalents required for oxidative phosphorylatio...
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2016
Substantial increases in cardiac output (CO), stroke volume (SV), and gastrointestinal blood flow... more Substantial increases in cardiac output (CO), stroke volume (SV), and gastrointestinal blood flow are essential for euryhaline rainbow trout ( Oncorhyncus mykiss) osmoregulation in seawater. However, the underlying hemodynamic mechanisms responsible for these changes are unknown. By examining a range of circulatory and cardiac morphological variables of seawater- and freshwater-acclimated rainbow trout, the present study revealed a significantly higher central venous pressure (CVP) in seawater-acclimated trout (~0.09 vs. −0.02 kPa). This serves to increase cardiac end-diastolic volume in seawater and explains the elevations in SV (~0.41 vs. 0.27 ml/kg) and CO (~21.5 vs. 14.2 ml·min−1·kg−1) when compared with trout in freshwater. Furthermore, these hemodynamic modifications coincided with a significant increase in the proportion of compact myocardium, which may be necessary to compensate for the increased wall tension associated with a larger stroke volume. Following a temperature in...
The Journal of experimental biology, Jul 5, 2017
Stress and elevated cortisol levels are associated with pathological heart growth and cardiovascu... more Stress and elevated cortisol levels are associated with pathological heart growth and cardiovascular disease in humans and other mammals. We recently established a link between heritable variation in post-stress cortisol production and cardiac growth also in salmonid fish. A conserved stimulatory effect of the otherwise catabolic steroid hormone cortisol is likely implied, but has to date not been established experimentally. Furthermore, whereas cardiac growth is associated with failure of the mammalian heart, pathological cardiac hypertrophy has not previously been described in fish. Here we show that rainbow trout (Oncorhynchus mykiss) treated with cortisol in the food for 45 days have enlarged hearts with lower maximum stroke volume and cardiac output. In accordance with impaired cardiac performance, overall circulatory oxygen transporting capacity was diminished as indicated by reduced aerobic swimming performance. In contrast to the well-known adaptive/physiological heart growt...
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Papers by Andreas Ekström