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William Davison - One of the best experts on this subject based on the ideXlab platform.
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Cold Physiology: Postprandial Blood Flow Dynamics and Metabolism in the Antarctic Fish Pagothenia borchgrevinki
2013Co-Authors: Erik S, William Davison, M. AxelssonAbstract:Previous studies on metabolic responses to feeding (i.e. the specific dynamic action, SDA) in Antarctic fishes living at temperatures below zero have reported long-lasting increases and small peak responses. We therefore hypothesized that the postprandial hyperemia also would be limited in the Antarctic fish Pagothenia borchgrevinki. The proportion of cardiac output directed to the splanchnic circulation in unfed fish was 18%, which is similar to temperate fish species. Contrary to our prediction, however, gastrointestinal blood flow had increased by 88 % at twenty four hours after feeding due to a significant increase in cardiac output and a significant decrease in gastrointestinal vascular resistance. While gastric evacuation time appeared to be longer than in comparable temperate species, digestion had clearly commenced twenty four hours after feeding as judged by a reduction in mass of the administered feed. Even so, oxygen consumption did not increase suggesting an unusually slowly developing SDA. Adrenaline and angiotensin II was injected into unfed fish to investigate neuro-humoral control mechanisms of gastrointestinal blood flow. Both agonists increased gastrointestinal vascular resistance and arterial blood pressure, while systemic vascular resistance was largely unaffected. The hypertension was mainly due to increased cardiac output revealing that the heart and the gastrointestinal vasculature, but not the somatic vasculature, are important targets for these agonists. It is suggested that the apparently reduced SDA in P. borchgrevinki is due to a depressant effect of the low temperature on protein assimilation processes occurring outside o
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cold physiology postprandial blood flow dynamics and metabolism in the antarctic fish Pagothenia borchgrevinki
PLOS ONE, 2012Co-Authors: Erik Sandblom, William Davison, M. AxelssonAbstract:Previous studies on metabolic responses to feeding (i.e. the specific dynamic action, SDA) in Antarctic fishes living at temperatures below zero have reported long-lasting increases and small peak responses. We therefore hypothesized that the postprandial hyperemia also would be limited in the Antarctic fish Pagothenia borchgrevinki. The proportion of cardiac output directed to the splanchnic circulation in unfed fish was 18%, which is similar to temperate fish species. Contrary to our prediction, however, gastrointestinal blood flow had increased by 88% at twenty four hours after feeding due to a significant increase in cardiac output and a significant decrease in gastrointestinal vascular resistance. While gastric evacuation time appeared to be longer than in comparable temperate species, digestion had clearly commenced twenty four hours after feeding as judged by a reduction in mass of the administered feed. Even so, oxygen consumption did not increase suggesting an unusually slowly developing SDA. Adrenaline and angiotensin II was injected into unfed fish to investigate neuro-humoral control mechanisms of gastrointestinal blood flow. Both agonists increased gastrointestinal vascular resistance and arterial blood pressure, while systemic vascular resistance was largely unaffected. The hypertension was mainly due to increased cardiac output revealing that the heart and the gastrointestinal vasculature, but not the somatic vasculature, are important targets for these agonists. It is suggested that the apparently reduced SDA in P. borchgrevinki is due to a depressant effect of the low temperature on protein assimilation processes occurring outside of the gastrointestinal tract, while the gastrointestinal blood flow responses to feeding and vasoactive substances resemble those previously observed in temperate species.
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nervous and humoral catecholaminergic control of blood pressure and cardiac performance in the antarctic fish Pagothenia borchgrevinki
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2010Co-Authors: Erik Sandblom, William Davison, Catharina Olsson, M. AxelssonAbstract:The role of circulating and neural catecholamines for cardiovascular control in the Antarctic fish Pagothenia borchgrevinki was studied in vivo using pharmacological tools and with immunohistochemistry on isolated tissues. Adrenergic nerve blockade with bretylium decreased dorsal aortic pressure (Pda) and systemic vascular resistance (Rsys), while cardiac output (Q) did not change. The blockade of α-adrenoceptors with phentolamine reduced Pda and Rsys further, revealing that vasomotor tone was influenced by circulating catecholamines in bretylium treated fish. The physiological evidence for an adrenergic nervous control of the vasculature was corroborated by the presence of tyrosine hydroxylase (TH)-immunoreactive fibres associated with blood vessels in spleen, gonads and gastrointestinal tract. TH-immunoreactive fibres were not observed in the atrium and ventricle, but a dense population of TH-immunoreactive fibres was apparent in the bulbus arteriosus. The present study suggests that an adrenergic nervous mechanism is responsible for maintaining vasomotor tone in P. borchgrevinki. While experiments failed to demonstrate a tonic adrenergic nervous influence affecting cardiac performance, an adrenergic nervous control of bulbar compliance may be essential for optimizing gill blood flow dynamics in this species, which has a high relative stroke volume and displays profound changes in stroke volume in vivo.
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Circulatory function at sub-zero temperature: venous responses to catecholamines and angiotensin II in the Antarctic fish Pagothenia borchgrevinki
Journal of Comparative Physiology B, 2009Co-Authors: Erik Sandblom, M. Axelsson, William DavisonAbstract:Catecholamines increase arterial pressure by increasing cardiac output ( Q ) and stroke volume ( V _s), while angiotensin II (ang II) also increases vascular resistance ( R _sys) in the Antarctic fish Pagothenia borchgrevinki . Adrenaline, phenylephrine and ang II (Asn^1, Val^5) were injected into P. borchgrevinki . Cardiovascular variables, including central venous pressure ( P _cv) and mean circulatory filling pressure ( P _mcf; an index of venous capacitance), were recorded to investigate if venous vasoconstriction can explain the increased V _s and Q and the arterial pressor response in this species. Routine P _cv and P _mcf were 0.11 ± 0.01 and 0.18 ± 0.02 kPa, respectively. All of the drugs caused moderate increases in P _cv and P _mcf and the responses were attenuated after α-adrenergic blockade with prazosin. Although dorsal aortic pressure ( P _da) also increased in response to all agonists, the mechanisms differed. Adrenaline caused sustained increases in V _s and Q , while R _sys only rose transiently. Ang II had a slower effect than adrenaline and increased both R _sys and Q , while phenylephrine only increased R _sys. This study demonstrates that P _cv is positive and controlled by an α-adrenergic mechanism in P. borchgrevinki . However, given the relatively small venous response to adrenaline it seems more likely that the increases in V _s and Q from this agonist are due to direct effects on the heart.
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enforced exercise but not acute temperature elevation decreases venous capacitance in the stenothermal antarctic fish Pagothenia borchgrevinki
Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, 2008Co-Authors: Erik Sandblom, M. Axelsson, William DavisonAbstract:The venous haemodynamic response to enforced exercise and acute temperature increase was examined in the Antarctic fish Pagothenia borchgrevinki (borch) to enable comparisons with the existing literature for temperate species, and investigate if the unusual cardiovascular response to temperature changes previously observed in the borch can be linked to an inability to regulate the venous vasculature. Routine central venous blood pressure (P cv) was 0.08 kPa and the mean circulatory filling pressure (P mcf; an index of venous capacitance) was 0.14 kPa. Acute warming from 0 to 2.5 and 5°C increased heart rate (f H), while dorsal aortic blood pressure (P da) decreased. P mcf did not change, while P cv decreased significantly at 5°C. This contrasts with the venoconstriction previously observed in rainbow trout in response to increased temperature. Exercise resulted in small increases in P mcf and P cv, a response that was abolished by α-adrenoceptor blockade. This study demonstrates that the heart of P. borchgrevinki normally operates at positive filling pressures (i.e. P cv) and that venous capacitance can be actively regulated by an α-adrenergic mechanism. The lack of decrease in venous capacitance during warming may suggest that a small increase in venous tone is offset by a passive temperature-mediated increase in compliance.
M. Axelsson - One of the best experts on this subject based on the ideXlab platform.
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Cold Physiology: Postprandial Blood Flow Dynamics and Metabolism in the Antarctic Fish Pagothenia borchgrevinki
2013Co-Authors: Erik S, William Davison, M. AxelssonAbstract:Previous studies on metabolic responses to feeding (i.e. the specific dynamic action, SDA) in Antarctic fishes living at temperatures below zero have reported long-lasting increases and small peak responses. We therefore hypothesized that the postprandial hyperemia also would be limited in the Antarctic fish Pagothenia borchgrevinki. The proportion of cardiac output directed to the splanchnic circulation in unfed fish was 18%, which is similar to temperate fish species. Contrary to our prediction, however, gastrointestinal blood flow had increased by 88 % at twenty four hours after feeding due to a significant increase in cardiac output and a significant decrease in gastrointestinal vascular resistance. While gastric evacuation time appeared to be longer than in comparable temperate species, digestion had clearly commenced twenty four hours after feeding as judged by a reduction in mass of the administered feed. Even so, oxygen consumption did not increase suggesting an unusually slowly developing SDA. Adrenaline and angiotensin II was injected into unfed fish to investigate neuro-humoral control mechanisms of gastrointestinal blood flow. Both agonists increased gastrointestinal vascular resistance and arterial blood pressure, while systemic vascular resistance was largely unaffected. The hypertension was mainly due to increased cardiac output revealing that the heart and the gastrointestinal vasculature, but not the somatic vasculature, are important targets for these agonists. It is suggested that the apparently reduced SDA in P. borchgrevinki is due to a depressant effect of the low temperature on protein assimilation processes occurring outside o
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cold physiology postprandial blood flow dynamics and metabolism in the antarctic fish Pagothenia borchgrevinki
PLOS ONE, 2012Co-Authors: Erik Sandblom, William Davison, M. AxelssonAbstract:Previous studies on metabolic responses to feeding (i.e. the specific dynamic action, SDA) in Antarctic fishes living at temperatures below zero have reported long-lasting increases and small peak responses. We therefore hypothesized that the postprandial hyperemia also would be limited in the Antarctic fish Pagothenia borchgrevinki. The proportion of cardiac output directed to the splanchnic circulation in unfed fish was 18%, which is similar to temperate fish species. Contrary to our prediction, however, gastrointestinal blood flow had increased by 88% at twenty four hours after feeding due to a significant increase in cardiac output and a significant decrease in gastrointestinal vascular resistance. While gastric evacuation time appeared to be longer than in comparable temperate species, digestion had clearly commenced twenty four hours after feeding as judged by a reduction in mass of the administered feed. Even so, oxygen consumption did not increase suggesting an unusually slowly developing SDA. Adrenaline and angiotensin II was injected into unfed fish to investigate neuro-humoral control mechanisms of gastrointestinal blood flow. Both agonists increased gastrointestinal vascular resistance and arterial blood pressure, while systemic vascular resistance was largely unaffected. The hypertension was mainly due to increased cardiac output revealing that the heart and the gastrointestinal vasculature, but not the somatic vasculature, are important targets for these agonists. It is suggested that the apparently reduced SDA in P. borchgrevinki is due to a depressant effect of the low temperature on protein assimilation processes occurring outside of the gastrointestinal tract, while the gastrointestinal blood flow responses to feeding and vasoactive substances resemble those previously observed in temperate species.
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nervous and humoral catecholaminergic control of blood pressure and cardiac performance in the antarctic fish Pagothenia borchgrevinki
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2010Co-Authors: Erik Sandblom, William Davison, Catharina Olsson, M. AxelssonAbstract:The role of circulating and neural catecholamines for cardiovascular control in the Antarctic fish Pagothenia borchgrevinki was studied in vivo using pharmacological tools and with immunohistochemistry on isolated tissues. Adrenergic nerve blockade with bretylium decreased dorsal aortic pressure (Pda) and systemic vascular resistance (Rsys), while cardiac output (Q) did not change. The blockade of α-adrenoceptors with phentolamine reduced Pda and Rsys further, revealing that vasomotor tone was influenced by circulating catecholamines in bretylium treated fish. The physiological evidence for an adrenergic nervous control of the vasculature was corroborated by the presence of tyrosine hydroxylase (TH)-immunoreactive fibres associated with blood vessels in spleen, gonads and gastrointestinal tract. TH-immunoreactive fibres were not observed in the atrium and ventricle, but a dense population of TH-immunoreactive fibres was apparent in the bulbus arteriosus. The present study suggests that an adrenergic nervous mechanism is responsible for maintaining vasomotor tone in P. borchgrevinki. While experiments failed to demonstrate a tonic adrenergic nervous influence affecting cardiac performance, an adrenergic nervous control of bulbar compliance may be essential for optimizing gill blood flow dynamics in this species, which has a high relative stroke volume and displays profound changes in stroke volume in vivo.
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Circulatory function at sub-zero temperature: venous responses to catecholamines and angiotensin II in the Antarctic fish Pagothenia borchgrevinki
Journal of Comparative Physiology B, 2009Co-Authors: Erik Sandblom, M. Axelsson, William DavisonAbstract:Catecholamines increase arterial pressure by increasing cardiac output ( Q ) and stroke volume ( V _s), while angiotensin II (ang II) also increases vascular resistance ( R _sys) in the Antarctic fish Pagothenia borchgrevinki . Adrenaline, phenylephrine and ang II (Asn^1, Val^5) were injected into P. borchgrevinki . Cardiovascular variables, including central venous pressure ( P _cv) and mean circulatory filling pressure ( P _mcf; an index of venous capacitance), were recorded to investigate if venous vasoconstriction can explain the increased V _s and Q and the arterial pressor response in this species. Routine P _cv and P _mcf were 0.11 ± 0.01 and 0.18 ± 0.02 kPa, respectively. All of the drugs caused moderate increases in P _cv and P _mcf and the responses were attenuated after α-adrenergic blockade with prazosin. Although dorsal aortic pressure ( P _da) also increased in response to all agonists, the mechanisms differed. Adrenaline caused sustained increases in V _s and Q , while R _sys only rose transiently. Ang II had a slower effect than adrenaline and increased both R _sys and Q , while phenylephrine only increased R _sys. This study demonstrates that P _cv is positive and controlled by an α-adrenergic mechanism in P. borchgrevinki . However, given the relatively small venous response to adrenaline it seems more likely that the increases in V _s and Q from this agonist are due to direct effects on the heart.
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enforced exercise but not acute temperature elevation decreases venous capacitance in the stenothermal antarctic fish Pagothenia borchgrevinki
Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, 2008Co-Authors: Erik Sandblom, M. Axelsson, William DavisonAbstract:The venous haemodynamic response to enforced exercise and acute temperature increase was examined in the Antarctic fish Pagothenia borchgrevinki (borch) to enable comparisons with the existing literature for temperate species, and investigate if the unusual cardiovascular response to temperature changes previously observed in the borch can be linked to an inability to regulate the venous vasculature. Routine central venous blood pressure (P cv) was 0.08 kPa and the mean circulatory filling pressure (P mcf; an index of venous capacitance) was 0.14 kPa. Acute warming from 0 to 2.5 and 5°C increased heart rate (f H), while dorsal aortic blood pressure (P da) decreased. P mcf did not change, while P cv decreased significantly at 5°C. This contrasts with the venoconstriction previously observed in rainbow trout in response to increased temperature. Exercise resulted in small increases in P mcf and P cv, a response that was abolished by α-adrenoceptor blockade. This study demonstrates that the heart of P. borchgrevinki normally operates at positive filling pressures (i.e. P cv) and that venous capacitance can be actively regulated by an α-adrenergic mechanism. The lack of decrease in venous capacitance during warming may suggest that a small increase in venous tone is offset by a passive temperature-mediated increase in compliance.
Craig E. Franklin - One of the best experts on this subject based on the ideXlab platform.
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antarctic fish can compensate for rising temperatures thermal acclimation of cardiac performance in Pagothenia borchgrevinki
The Journal of Experimental Biology, 2007Co-Authors: Craig E. Franklin, William Davison, Frank SeebacherAbstract:Antarctic fish Pagothenia borchgrevinki in McMurdo Sound, Antarctica, inhabit one of the coldest and most thermally stable of all environments. Sea temperatures under the sea ice in this region remain a fairly constant -1.86 degrees C year round. This study examined the thermal plasticity of cardiac function in P. borchgrevinki to determine whether specialisation to stable low temperatures has led to the loss of the ability to acclimate physiological function. Fish were acclimated to - 1 degrees C and 4 degrees C for 4 - 5 weeks and cardiac output was measured at rest and after exhaustive exercise in fish acutely transferred from their acclimation temperature to - 1, 2, 4, 6 and 8 degrees C. In the - 1 degrees C acclimated fish, the factorial scope for cardiac output was greatest at - 1 degrees C and decreased with increasing temperature. Increases in cardiac output with exercise in the - 1 degrees C acclimated fish was achieved by increases in both heart rate and stroke volume. With acclimation to 4 degrees C, resting cardiac output was thermally independent across the test temperatures; furthermore, factorial scope for cardiac output was maintained at 4, 6 and 8 degrees C, demonstrating thermal compensation of cardiac function at the higher temperatures. This was at the expense of cardiac function at - 1 degrees C, where there was a significant decrease in factorial scope for cardiac output in the 4 degrees C acclimated fish. Increases in cardiac output with exercise in the 4 degrees C acclimated fish at the higher temperatures was achieved by changes in heart rate alone, with stroke volume not varying between rest and exercise. The thermal compensation of cardiac function in P. borchgrevinki at higher temperatures was the result of a change in pumping strategy from a mixed inotropic/chronotropic modulated heart in - 1 degrees C acclimated fish at low temperatures to a purely chronotropic modulated heart in the 4 degrees C acclimated fish at higher temperatures. In spite of living in a highly stenothermal cold environment, P. borchgrevinki demonstrated the capacity to thermally acclimate cardiac function to elevated temperatures, thereby allowing the maintenance of factorial scope and the support of aerobic swimming at higher temperatures.
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a falsification of the thermal specialization paradigm compensation for elevated temperatures in antarctic fishes
Biology Letters, 2005Co-Authors: Frank Seebacher, William Davison, Cara J Lowe, Craig E. FranklinAbstract:Specialization to a particular environment is one of the main factors used to explain species distributions. Antarctic fishes are often cited as a classic example to illustrate the specialization process and are regarded as the archetypal stenotherms. Here we show that the Antarctic fish Pagothenia borchgrevinki has retained the capacity to compensate for chronic temperature change. By displaying astounding plasticity in cardiovascular response and metabolic control, the fishes maintained locomotory performance at elevated temperatures. Our falsification of the specialization paradigm indicates that the effect of climate change on species distribution and extinction may be overestimated by current models of global warming.
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hypertension in Pagothenia borchgrevinki caused by x cell disease
Journal of Fish Biology, 2003Co-Authors: William Davison, Craig E. FranklinAbstract:Approximately 15% of a population of the cryopelagic nototheniid fish Pagothenia borchgrevinki, found constantly swimming immediately beneath the annual fast ice, in McMudro Sound. Ross Sea, Antarctica, was affected by X-cell gill disease. This disease affected blood flow through the gill lamellae, and this in turn affected oxygen uptake. Exercise caused increases in heart rate and ventral aortic blood pressure. Heart rate increased from 15.1 +/- 1.55 to 23.1 +/- 0.93 beats min(-1) in healthy fish, with a similar increase from 15.1 +/- 1.55 to 23.1 +/- 0.93 beats min(-1) in healthy fish, with a similar increase (to 24.6 +/- 0.26 beats min(-1)) in X-cell-affected animals. In healthy fish, pressures rose with exercise (from 2.72 +/- 0.11 to 3.75 +/- 0.19 kPa) and then rapidly returned to resting levels during recovery. In X-cell fish pressures rose during exercise, but then continued to rise, to reach a high of 4.18 +/- 0.13 kPa, close to the predicted maximum pressure able to be generated by these hearts. Recovery was rapid in healthy fish, but was prolonged in diseased animals. As they are constantly swimming, there is the potential that X-cell-affected fish suffer from chronic hypertension. (C) 2003 The Fisheries Society of the British Isles.
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constancy and control of heart rate during an increase in temperature in the antarctic fish Pagothenia borchgrevinki
Experimental Biology Online, 2001Co-Authors: Craig E. Franklin, M. Axelsson, William DavisonAbstract:The effect of an acute temperature increase on the control of the heart of the Antarctic teleost Pagothenia borchgrevinki was examined. Heart rate was thermally independent over the range −1.2°C to 3°C, although increasing the temperature from −1.2°C to 3°C elicited a decrease in ventral aortic pressure. Administration of the muscarinic receptor antagonist atropine and the β-adrenoreceptor antagonist sotalol abolished the thermal independence of heart rate, with heart rate increasing at Q10=2. As temperature was increased from −1.2°C to 3°C, cholinergic tone on the heart also increased, from 44.6±4.2% to 70.0±8.4%. At the same time the adrenergic tone increased from 35.5±3.3% to 43.0±3.1%, but the effect on the heart was masked by the increase of cholinergic tone, leading to the thermal independence of heart rate.
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Haematological changes in an Antarctic teleost, Trematomus bernacchii, following stress
Polar Biology, 1994Co-Authors: William Davison, Craig E. Franklin, Jan C MckenzieAbstract:The effect of an acute increase in temperature, exhaustive exercise and hypoxia on the haematology of the benthic Antarctic teleost, Trematomus bernacchii was investigated. High temperature and hypoxia caused the biggest changes to the blood, with increases in haematocrit, haemoglobin concentrations and plasma chloride levels. The spleen decreased in mass. Exercise produced the smallest changes. Changes were substantially less than reported for the more active cryopelagic species Pagothenia borchgrevinki . The magnitude of the haematocrit increase is discussed in relation to life-style of fish living in the Antarctic.
Erik Sandblom - One of the best experts on this subject based on the ideXlab platform.
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cold physiology postprandial blood flow dynamics and metabolism in the antarctic fish Pagothenia borchgrevinki
PLOS ONE, 2012Co-Authors: Erik Sandblom, William Davison, M. AxelssonAbstract:Previous studies on metabolic responses to feeding (i.e. the specific dynamic action, SDA) in Antarctic fishes living at temperatures below zero have reported long-lasting increases and small peak responses. We therefore hypothesized that the postprandial hyperemia also would be limited in the Antarctic fish Pagothenia borchgrevinki. The proportion of cardiac output directed to the splanchnic circulation in unfed fish was 18%, which is similar to temperate fish species. Contrary to our prediction, however, gastrointestinal blood flow had increased by 88% at twenty four hours after feeding due to a significant increase in cardiac output and a significant decrease in gastrointestinal vascular resistance. While gastric evacuation time appeared to be longer than in comparable temperate species, digestion had clearly commenced twenty four hours after feeding as judged by a reduction in mass of the administered feed. Even so, oxygen consumption did not increase suggesting an unusually slowly developing SDA. Adrenaline and angiotensin II was injected into unfed fish to investigate neuro-humoral control mechanisms of gastrointestinal blood flow. Both agonists increased gastrointestinal vascular resistance and arterial blood pressure, while systemic vascular resistance was largely unaffected. The hypertension was mainly due to increased cardiac output revealing that the heart and the gastrointestinal vasculature, but not the somatic vasculature, are important targets for these agonists. It is suggested that the apparently reduced SDA in P. borchgrevinki is due to a depressant effect of the low temperature on protein assimilation processes occurring outside of the gastrointestinal tract, while the gastrointestinal blood flow responses to feeding and vasoactive substances resemble those previously observed in temperate species.
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nervous and humoral catecholaminergic control of blood pressure and cardiac performance in the antarctic fish Pagothenia borchgrevinki
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2010Co-Authors: Erik Sandblom, William Davison, Catharina Olsson, M. AxelssonAbstract:The role of circulating and neural catecholamines for cardiovascular control in the Antarctic fish Pagothenia borchgrevinki was studied in vivo using pharmacological tools and with immunohistochemistry on isolated tissues. Adrenergic nerve blockade with bretylium decreased dorsal aortic pressure (Pda) and systemic vascular resistance (Rsys), while cardiac output (Q) did not change. The blockade of α-adrenoceptors with phentolamine reduced Pda and Rsys further, revealing that vasomotor tone was influenced by circulating catecholamines in bretylium treated fish. The physiological evidence for an adrenergic nervous control of the vasculature was corroborated by the presence of tyrosine hydroxylase (TH)-immunoreactive fibres associated with blood vessels in spleen, gonads and gastrointestinal tract. TH-immunoreactive fibres were not observed in the atrium and ventricle, but a dense population of TH-immunoreactive fibres was apparent in the bulbus arteriosus. The present study suggests that an adrenergic nervous mechanism is responsible for maintaining vasomotor tone in P. borchgrevinki. While experiments failed to demonstrate a tonic adrenergic nervous influence affecting cardiac performance, an adrenergic nervous control of bulbar compliance may be essential for optimizing gill blood flow dynamics in this species, which has a high relative stroke volume and displays profound changes in stroke volume in vivo.
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Circulatory function at sub-zero temperature: venous responses to catecholamines and angiotensin II in the Antarctic fish Pagothenia borchgrevinki
Journal of Comparative Physiology B, 2009Co-Authors: Erik Sandblom, M. Axelsson, William DavisonAbstract:Catecholamines increase arterial pressure by increasing cardiac output ( Q ) and stroke volume ( V _s), while angiotensin II (ang II) also increases vascular resistance ( R _sys) in the Antarctic fish Pagothenia borchgrevinki . Adrenaline, phenylephrine and ang II (Asn^1, Val^5) were injected into P. borchgrevinki . Cardiovascular variables, including central venous pressure ( P _cv) and mean circulatory filling pressure ( P _mcf; an index of venous capacitance), were recorded to investigate if venous vasoconstriction can explain the increased V _s and Q and the arterial pressor response in this species. Routine P _cv and P _mcf were 0.11 ± 0.01 and 0.18 ± 0.02 kPa, respectively. All of the drugs caused moderate increases in P _cv and P _mcf and the responses were attenuated after α-adrenergic blockade with prazosin. Although dorsal aortic pressure ( P _da) also increased in response to all agonists, the mechanisms differed. Adrenaline caused sustained increases in V _s and Q , while R _sys only rose transiently. Ang II had a slower effect than adrenaline and increased both R _sys and Q , while phenylephrine only increased R _sys. This study demonstrates that P _cv is positive and controlled by an α-adrenergic mechanism in P. borchgrevinki . However, given the relatively small venous response to adrenaline it seems more likely that the increases in V _s and Q from this agonist are due to direct effects on the heart.
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enforced exercise but not acute temperature elevation decreases venous capacitance in the stenothermal antarctic fish Pagothenia borchgrevinki
Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, 2008Co-Authors: Erik Sandblom, M. Axelsson, William DavisonAbstract:The venous haemodynamic response to enforced exercise and acute temperature increase was examined in the Antarctic fish Pagothenia borchgrevinki (borch) to enable comparisons with the existing literature for temperate species, and investigate if the unusual cardiovascular response to temperature changes previously observed in the borch can be linked to an inability to regulate the venous vasculature. Routine central venous blood pressure (P cv) was 0.08 kPa and the mean circulatory filling pressure (P mcf; an index of venous capacitance) was 0.14 kPa. Acute warming from 0 to 2.5 and 5°C increased heart rate (f H), while dorsal aortic blood pressure (P da) decreased. P mcf did not change, while P cv decreased significantly at 5°C. This contrasts with the venoconstriction previously observed in rainbow trout in response to increased temperature. Exercise resulted in small increases in P mcf and P cv, a response that was abolished by α-adrenoceptor blockade. This study demonstrates that the heart of P. borchgrevinki normally operates at positive filling pressures (i.e. P cv) and that venous capacitance can be actively regulated by an α-adrenergic mechanism. The lack of decrease in venous capacitance during warming may suggest that a small increase in venous tone is offset by a passive temperature-mediated increase in compliance.
M.e. Forster - One of the best experts on this subject based on the ideXlab platform.
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cardiovascular responses to adenosine in the antarctic fish Pagothenia borchgrevinki
The Journal of Experimental Biology, 1999Co-Authors: L Sundin, M. Axelsson, William Davison, M.e. ForsterAbstract:We have investigated the effects of adenosine on the cardiovascular system of the Antarctic fish Pagothenia borchgrevinki. Continuous measurements of ventral and dorsal aortic blood pressures, heart rate (fh) and ventral aortic blood flow (cardiac output, q_dot ) were made using standard cannulation techniques and a single-crystal Doppler flowmeter. On line measurements of arterial P(O2) were made using an oxygen electrode connected to an extracorporeal loop. Adenosine (10 nmol kg(-)(1)) and the specific A(1)-receptor agonist N(6)-cyclopentyladenosine (CPA) elicited biphasic changes in the branchial and systemic resistances. While there was an initial decrease in the branchial resistance followed by an increase, the opposite was true for the systemic response. The resistance changes were significantly attenuated by aminophylline (a P(1)-receptor antagonist) and 8-cyclopentyltheophylline (CPT; an A(1)-receptor antagonist). In addition, adenosine induced an aminophylline-sensitive decrease in the arterial P(O2). The reduction was attenuated when pre-injection arterial P(O2) was low. Adenosine and CPA also caused a marked reduction in fh, with CPA being more potent. The bradycardia was blocked by aminophylline and CPT, demonstrating an involvement of A(1) receptors in this response.
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Effects of serotonin, adrenaline and other vasoactive drugs on the branchial blood vessels of the Antarctic fish Pagothenia borchgrevinki
Fish Physiology and Biochemistry, 1998Co-Authors: M.e. Forster, A.h. Forster, W. DavisonAbstract:Myography and an isolated, perfused gill arch preparation were used to investigate the actions of drugs on the gill vasculature of an Antarctic teleost fish, Pagothenia borchgrevinki. Serotonin produced a dose-dependent vasoconstriction of the afferant branchial arteries, the gill arch and the efferent branchial arteries, and was the most potent vasoconstrictor tested. Acetylcholine, at concentrations exceeding 1 × 10^-6M, vasoconstricted the gill arch, but had a negligible effect on the branchial arteries. The responses to adrenaline, with and without the β-adrenergic blocking drug, sotalol and the effects of the β-adrenergic agonist drug isoprenaline indicated the presence of both α-adrenergic and β-adrenergic receptors in the gill vasculature, with the vasoconstrictory action of the former predominating in the efferent vasculature. Angiotensin II was without effect in either preparation. The results are a further demonstration of the dominance of vasoconstrictory responses in the control of gill cular resistance in P. borchgrevinki: which has been associated previously with the sub-zero temperatures at which the animals are found.
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Catecholamine release in heat-stressed Antarctic fish causes proton extrusion by the red cells
'Springer Science and Business Media LLC', 1998Co-Authors: M.e. Forster, Davison W, Ce Franklin, Axelsson M, Sundin L, Gieseg SAbstract:Two species of Antarctic fish were stressed by moving them from seawater at -1 degrees C to seawater at 10 degrees C and holding them for a period of 10 min. The active cryopelagic species Pagothenia borchgrevinki maintained heart rate while in the benthic species Trematomus bernacchii there was an increase in heart rate. Blood pressure did not change in either species. Both species released catecholamines into the circulation as a consequence of the stress. P. borchgrevinki released the greater amounts, having mean plasma concentrations of 177 +/- 54 nmol.l(-1) noradrenaline and 263 +/- 131 nmol.l(-1) adrenaline at 10 min. Pla.sma noradrenaline concentrations rose to 47 +/- 14 nmol.l(-1) and adrenaline to 73 +/- 28 nmol.l(-1) in T. bernacchii. Blood from P. borchgrevinki was tonometered in the presence of isoprenaline. A fall in extracellular pH suggests the presence of a Na+/H+ antiporter on the red cell membrane, the first demonstration of this in an Antarctic fish. Treatment with the beta-adrenergic antagonist drug sotalol inhibited swelling of red blood cells taken from temperature-stressed P. borchgrevinki, suggesting that the antiporter responds to endogenous catecholamines
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nervous control of the spleen in the red blooded antarctic fish Pagothenia borchgrevinki
American Journal of Physiology-regulatory Integrative and Comparative Physiology, 1996Co-Authors: S Nilsson, M.e. Forster, William Davison, M. AxelssonAbstract:The mechanisms of splenic control in the Antarctic fish, Pagothenia borchgrevinki, were investigated using isolated spleen and mesenteric artery strips in vitro and perfused spleen preparations in situ. Splenosomatic index (SSI) [100 x (spleen wt/body wt)] and hematocrit were determined in animals treated with atropine and phentolamine. Atropine injection increased the SSI from 0.60 +/- 0.06 to 0.89 +/- 0.04, whereas phentolamine decreased SSI to 0.45 +/- 0.03. In atropine-injected fish, hematocrit was 18.6 +/- 1.4 before and 6.6 +/- 0.8% 3 h after injection. Electrical stimulation of the splenic nerves produced biphasic flow responses. In 11 of 12 tested preparations, atropine (3 x 10(-7) to 10(-6) M) abolished the response, suggesting a major cholinergic component in the splenic innervation. Isolated spleen strip preparations contracted in response to carbachol, a response that was antagonized by atropine. The response to acetylcholine was markedly enhanced by the specific cholinesterase inhibitor BW-284c51. Catecholamine effects were somewhat irregular, and maximal contraction force with epinephrine and norepinephrine was 41 and 56%, respectively, of the carbachol response. The results suggest a mainly, if not solely, cholinergic autonomic control of the borch spleen, and a major function of the cholinergic innervation in the control of hematocrit in this species.
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blood pressure control in the antarctic fish Pagothenia borchgrevinki
The Journal of Experimental Biology, 1994Co-Authors: M. Axelsson, M.e. Forster, Bill Davison, S NilssonAbstract:The mechanisms of cardiovascular control in the Antarctic fish Pagothenia borchgrevinki were investigated during rest and swimming exercise using pharmacological tools to reveal the nature of the control systems involved. Simultaneous and continuous recordings of ventral and dorsal aortic blood pressure, heart rate and ventral aortic blood flow (cardiac output) were made using standard cannulation procedures and a single-crystal Doppler flowmeter. Exercise produced a clear and consistent decrease in dorsal aortic blood pressure caused by a decrease in systemic vascular resistance. At the same time, ventral aortic blood pressure increased owing to the combined effects of a markedly increased cardiac output (by about 80 %) and branchial vasoconstriction. Judged from the effects of the alpha-adrenoceptor antagonist prazosin, control of the branchial vasculature involves an alpha-adrenoceptor-mediated vasoconstriction, in addition to more traditional cholinergic vasoconstrictor and ss-adrenoceptor-mediated dilatory mechanisms. The range of heart rates is large, from 3-4 beats min-1 in individual fish during hypertensive bradycardia to about 28 beats min-1 after atropine treatment. Both chronotropic and inotropic effects are responsible for a marked increase in cardiac output during exercise. The increase in blood pressure caused by adrenaline injection was due largely to an increase in cardiac output, while direct effects on the systemic vasculature were small and transient. The increase in cardiac output, in turn, was due solely to an adrenergic stimulation of stroke volume. A barostatic bradycardia, often seen in other vertebrates in response to adrenaline injection, was absent and it is possible that a decrease in heart rate was offset by direct adrenergic stimulation of the heart. Angiotensin II (Ang II) produced consistent hypertension by systemic vasoconstriction. In contrast to the effects of adrenaline injection, the hypertension caused by Ang II was accompanied by a marked bradycardia. This could be abolished by atropine, suggesting a cholinergic vagal reflex of the type found in other vertebrates. Angiotensin I also caused an elevated blood pressure, and this effect was abolished by the angiotensin converting enzyme inhibitor enalapril, demonstrating elements of an angiotensin-related cardiovascular control system.
