1
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Parker KS, El N, Buldo EC, MacCormack TJ. Mechanisms of PVP-functionalized silver nanoparticle toxicity in fish: Intravascular exposure disrupts cardiac pacemaker function and inhibits Na +/K +-ATPase activity in heart, but not gill. Comp Biochem Physiol C Toxicol Pharmacol 2024; 277:109837. [PMID: 38218567 DOI: 10.1016/j.cbpc.2024.109837] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Revised: 12/21/2023] [Accepted: 01/08/2024] [Indexed: 01/15/2024]
Abstract
Polyvinylpyrrolidone-functionalized silver nanoparticles (nAgPVP) are popular in consumer products for their colloidal stability and antimicrobial activity. Whole lake additions of nAgPVP cause long term, ecosystem-scale changes in fish populations but the mechanisms underlying this effect are unclear. We have previously shown that in fish, nAgPVP impairs cardiac contractility and Na+/K+-ATPase (NKA) activity in vitro, raising the possibility that heart dysfunction could underlie population-level exposure effects. The goal of this study was to determine if nAgPVP influences the control of heart rate (fh), blood pressure, or cardiac NKA activity in vivo. First, a dose-response curve for the effects of 5 nm nAgPVP on contractility was completed on isometrically contracting ventricular muscle preparations from Arctic char (Salvelinus alpinus) and showed that force production was lowest at 500 μg L-1 and maximum pacing frequency increased with nAgPVP concentration. Stroke volume, cardiac output, and power output were maintained in isolated working heart preparations from brook char (Salvelinus fontinalis) exposed to 700 μg L-1 nAgPVP. Both fh and blood pressure were elevated after 24 h in brook char injected with 700 μg kg body mass-1 nAgPVP and fh was insensitive to modulation with blockers of β-adrenergic and muscarinic cholinergic receptors. Na+/K+-ATPase activity was significantly lower in heart, but not gill of nAgPVP injected fish. The results indicate that nAgPVP influences cardiac function in vivo by disrupting regulation of the pacemaker and cardiomyocyte ionoregulation. Impaired fh regulation may prevent fish from appropriately responding to environmental or social stressors and affect their ability to survive.
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Affiliation(s)
- K S Parker
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada
| | - N El
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada
| | - E C Buldo
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada
| | - T J MacCormack
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada.
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2
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Dixon TAM, Rhyno ELM, El N, McGaw SP, Otley NA, Parker KS, Buldo EC, Pabody CM, Savoie M, Cockshutt A, Morash AJ, Lamarre SG, MacCormack TJ. Taurine depletion impairs cardiac function and affects tolerance to hypoxia and high temperatures in brook char (Salvelinus fontinalis). J Exp Biol 2023; 226:286891. [PMID: 36728502 DOI: 10.1242/jeb.245092] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Accepted: 01/20/2023] [Indexed: 02/03/2023]
Abstract
Physiological and environmental stressors can cause osmotic stress in fish hearts, leading to a reduction in intracellular taurine concentration. Taurine is a β-amino acid known to regulate cardiac function in other animal models but its role in fish has not been well characterized. We generated a model of cardiac taurine deficiency (TD) by feeding brook char (Salvelinus fontinalis) a diet enriched in β-alanine, which inhibits cardiomyocyte taurine uptake. Cardiac taurine levels were reduced by 21% and stress-induced changes in normal taurine handling were observed in TD brook char. Responses to exhaustive exercise and acute thermal and hypoxia tolerance were then assessed using a combination of in vivo, in vitro and biochemical approaches. Critical thermal maximum was higher in TD brook char despite significant reductions in maximum heart rate. In vivo, TD brook char exhibited a lower resting heart rate, blunted hypoxic bradycardia and a severe reduction in time to loss of equilibrium under hypoxia. In vitro function was similar between control and TD hearts under oxygenated conditions, but stroke volume and cardiac output were severely compromised in TD hearts under severe hypoxia. Aspects of mitochondrial structure and function were also impacted in TD permeabilized cardiomyocytes, but overall effects were modest. High levels of intracellular taurine are required to achieve maximum cardiac function in brook char and cardiac taurine efflux may be necessary to support heart function under stress. Taurine appears to play a vital, previously unrecognized role in supporting cardiovascular function and stress tolerance in fish.
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Affiliation(s)
- Toni-Anne M Dixon
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Emma-Lee M Rhyno
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Nir El
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Samuel P McGaw
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Nathan A Otley
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Katya S Parker
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Elena C Buldo
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Claire M Pabody
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Mireille Savoie
- Department of Biology, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Amanda Cockshutt
- Department of Chemistry, Saint Francis Xavier University, Antigonish, NS, Canada, B2G 2W5
| | - Andrea J Morash
- Department of Biology, Mount Allison University, Sackville, NB, Canada, E4L 1E4
| | - Simon G Lamarre
- Departement de Biologie, Université de Moncton, Moncton, NB, Canada, E1A 3E9
| | - Tyson J MacCormack
- Department of Chemistry and Biochemistry, Mount Allison University, Sackville, NB, Canada, E4L 1E4
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Guo YP, Pan SS. Exercise preconditioning improves electrocardiographic signs of myocardial ischemic/hypoxic injury and malignant arrhythmias occurring after exhaustive exercise in rats. Sci Rep 2022; 12:18772. [PMID: 36335157 PMCID: PMC9637115 DOI: 10.1038/s41598-022-23466-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 10/31/2022] [Indexed: 11/08/2022] Open
Abstract
Exercise preconditioning (EP) has a good myocardial protective effect. This study explored whether EP improves electrocardiographic (ECG) signs of myocardial ischemic/hypoxic injury and the occurrence of malignant arrhythmia after exhaustive exercise. A total of 120 male SD rats were randomly divided into the control group (group C), early exercise preconditioning group (group EEP), late exercise preconditioning group (group LEP), exhaustive exercise group (group EE), early exercise preconditioning + exhaustive exercise group (group EEP + EE) and late exercise preconditioning + exhaustive exercise group (group LEP + EE). Changes in heart rate (HR), ST segment, T wave and QT corrected (QTc) intervals on ECG; hematoxylin-basic fuchsin-picric acid (HBFP) staining; and cTnI levels were used to study myocardial injury and the protective effect of EP. Compared with those in group C, the levels of plasma markers of myocardial injury, HBFP staining and ECG in group EE were significantly increased (P < 0.05). Compared with those in group EE, the levels of plasma markers of myocardial injury, HBFP staining and ECG in group EEP + EE and group LEP + EE were significantly decreased (P < 0.05). The results suggested that EP improved ECG signs of myocardial ischemic/hypoxic injury and malignant arrhythmias that occur after exhaustive exercise. The ST segment and T wave could also serve as indexes for evaluating exhaustive exercise-induced myocardial ischemia/hypoxia.
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Affiliation(s)
- Yuan-Pan Guo
- grid.412543.50000 0001 0033 4148School of Kinesiology, Shanghai University of Sport, 399 Changhai Road, Shanghai, 200438 China
| | - Shan-Shan Pan
- grid.412543.50000 0001 0033 4148School of Kinesiology, Shanghai University of Sport, 399 Changhai Road, Shanghai, 200438 China
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4
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Smith B, Crossley DA, Wang T, Joyce W. No evidence for pericardial restraint in the snapping turtle (Chelydra serpentina) following pharmacologically-induced bradycardia at rest or during exercise. Am J Physiol Regul Integr Comp Physiol 2022; 322:R389-R399. [PMID: 35200048 PMCID: PMC9018006 DOI: 10.1152/ajpregu.00004.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Most animals elevate cardiac output during exercise through a rise in heart rate (fH), whilst stroke volume (VS) remains relatively unchanged. Cardiac pacing reveals that elevating fH alone does not alter cardiac output, which is instead largely regulated by the peripheral vasculature. In terms of myocardial oxygen demand, an increase in fH is more costly than that which would incur if VS instead were to increase. We hypothesized that fH must increase because any substantial rise in VS would be constrained by the pericardium. To investigate this hypothesis, we explored the effects of pharmacologically-induced bradycardia, with ivabradine treatment, on VS at rest and during exercise in the common snapping turtle (Chelydra serpentina) with intact or opened pericardium. We first showed that, in isolated myocardial preparations, ivabradine exerted a pronounced positive inotropic effect on atrial tissue, but only minor effects on ventricle. Ivabradine reduced fH in vivo, such that exercise tachycardia was attenuated. Pulmonary and systemic VS rose in response to ivabradine. The rise in pulmonary VS largely compensated for the bradycardia at rest, leaving total pulmonary flow unchanged by ivabradine, although ivabradine reduced pulmonary blood flow during swimming (exercise x ivabradine interaction, P<0.05). Although systemic VS increased, systemic blood flow was reduced by ivabradine both at rest and during exercise, in spite of ivabradine's potential to increase cardiac contractility. Opening the pericardium had no effect on fH, VS or blood flows before or after ivabradine, indicating that the pericardium does not constrain VS in turtles, even during pharmacologically-induced bradycardia.
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Affiliation(s)
- Brandt Smith
- Department of Biological Sciences, University of North Texas, Denton, TX, United States
| | - Dane A Crossley
- Department of Biological Sciences, University of North Texas, Denton, TX, United States
| | - Tobias Wang
- Department of Biology- Zoophysiology, Aarhus University, Aarhus C, Denmark
| | - William Joyce
- Department of Biology- Zoophysiology, Aarhus University, Aarhus C, Denmark
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5
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Carnevale C, Syme DA, Gamperl AK. Effects of hypoxic acclimation, muscle strain, and contraction frequency on nitric oxide-mediated myocardial performance in steelhead trout ( Oncorhynchus mykiss). Am J Physiol Regul Integr Comp Physiol 2021; 320:R588-R610. [PMID: 33501888 DOI: 10.1152/ajpregu.00014.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Whether hypoxic acclimation influences nitric oxide (NO)-mediated control of fish cardiac function is not known. Thus, we measured the function/performance of myocardial strips from normoxic- and hypoxic-acclimated (40% air saturation; ∼8 kPa O2) trout at several frequencies (20-80 contractions·min-1) and two muscle strain amplitudes (8% and 14%) when exposed to increasing concentrations of the NO donor sodium nitroprusside (SNP) (10-9 to 10-4 M). Further, we examined the influence of 1) nitric oxide synthase (NOS) produced NO [by blocking NOS with 10-4 M NG-monomethyl-l-arginine (l-NMMA)] and 2) soluble guanylyl cyclase mediated, NOS-independent, NO effects (i.e., after blockade with 10-4 M ODQ), on myocardial contractility. Hypoxic acclimation increased twitch duration by 8%-10% and decreased mass-specific net power by ∼35%. However, hypoxic acclimation only had minor impacts on the effects of SNP and the two blockers on myocardial function. The most surprising finding of the current study was the degree to which contraction frequency and strain amplitude influenced NO-mediated effects on myocardial power. For example, at 8% strain, 10-4 SNP resulted in a decrease in net power of ∼30% at 20 min-1 but an increase of ∼20% at 80 min-1, and this effect was magnified at 14% strain. This research suggests that hypoxic acclimation has only minor effects on NO-mediated myocardial contractility in salmonids, is the first to report the high frequency- and strain-dependent nature of NO effects on myocardial contractility in fishes, and supports previous work showing that NO effects on the heart (myocardium) are finely tuned spatiotemporally.
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Affiliation(s)
- Christian Carnevale
- Department of Ocean Sciences and Biology, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
| | - Douglas A Syme
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - A Kurt Gamperl
- Department of Ocean Sciences and Biology, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
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Sutcliffe RL, Li S, Gilbert MJH, Schulte PM, Miller KM, Farrell AP. A rapid intrinsic heart rate resetting response with thermal acclimation in rainbow trout, Oncorhynchus mykiss. J Exp Biol 2020; 223:jeb215210. [PMID: 32345705 PMCID: PMC7328139 DOI: 10.1242/jeb.215210] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2019] [Accepted: 04/17/2020] [Indexed: 01/01/2023]
Abstract
We examined cardiac pacemaker rate resetting in rainbow trout following a reciprocal temperature transfer. In the original experiment, performed in winter, 4°C-acclimated fish transferred to 12°C reset intrinsic heart rate after just 1 h (from 56.8±1.2 to 50.8±1.5 beats min-1); 12°C-acclimated fish transferred to 4°C reset intrinsic heart rate after 8 h (from 33.4±0.7 to 37.7±1.2 beats min-1). However, in a replicate experiment, performed in the summer using a different brood year, intrinsic heart rate was not reset, even after 10 weeks at a new temperature. Using this serendipitous opportunity, we compared mRNA expression changes of a suite of proteins in sinoatrial node (SAN), atrial and ventricular tissues after both 1 h and longer than 3 weeks for both experimental acclimation groups to identify those changes only associated with pacemaker rate resetting. Of the changes in mRNA expression occurring after more than 3 weeks of warm acclimation and associated with pacemaker rate resetting, we observed downregulation of NKA α1c in the atrium and ventricle, and upregulation of HCN1 in the ventricle. However, in the SAN there were no mRNA expression changes unique to the fish with pacemaker rate resetting after either 1 h or 3 weeks of warm acclimation. Thus, despite identifying changes in mRNA expression of contractile cardiac tissues, there was an absence of changes in mRNA expression directly involved with the initial, rapid pacemaker rate resetting with warm acclimation. Importantly, pacemaker rate resetting with thermal acclimation does not always occur in rainbow trout.
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Affiliation(s)
- Rachel L Sutcliffe
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
| | - Shaorong Li
- Pacific Biological Station, Fisheries and Oceans, Nanaimo, BC, Canada, V9T 6N7
| | - Matthew J H Gilbert
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
| | - Patricia M Schulte
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
| | - Kristi M Miller
- Pacific Biological Station, Fisheries and Oceans, Nanaimo, BC, Canada, V9T 6N7
| | - Anthony P Farrell
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
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7
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Abstract
In the 1950s, Arthur C. Guyton removed the heart from its pedestal in cardiovascular physiology by arguing that cardiac output is primarily regulated by the peripheral vasculature. This is counterintuitive, as modulating heart rate would appear to be the most obvious means of regulating cardiac output. In this Review, we visit recent and classic advances in comparative physiology in light of this concept. Although most vertebrates increase heart rate when oxygen demands rise (e.g. during activity or warming), experimental evidence suggests that this tachycardia is neither necessary nor sufficient to drive a change in cardiac output (i.e. systemic blood flow, Q̇ sys) under most circumstances. Instead, Q̇ sys is determined by the interplay between vascular conductance (resistance) and capacitance (which is mainly determined by the venous circulation), with a limited and variable contribution from heart function (myocardial inotropy). This pattern prevails across vertebrates; however, we also highlight the unique adaptations that have evolved in certain vertebrate groups to regulate venous return during diving bradycardia (i.e. inferior caval sphincters in diving mammals and atrial smooth muscle in turtles). Going forward, future investigation of cardiovascular responses to altered metabolic rate should pay equal consideration to the factors influencing venous return and cardiac filling as to the factors dictating cardiac function and heart rate.
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Affiliation(s)
- William Joyce
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark .,Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
| | - Tobias Wang
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark
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8
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Marchant JL, Farrell AP. Membrane and calcium clock mechanisms contribute variably as a function of temperature to setting cardiac pacemaker rate in zebrafish Danio rerio. JOURNAL OF FISH BIOLOGY 2019; 95:1265-1274. [PMID: 31429079 DOI: 10.1111/jfb.14126] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Accepted: 08/19/2019] [Indexed: 06/10/2023]
Abstract
Here, we show that heart rate in zebrafish Danio rerio is dependent upon two pacemaking mechanisms and it possesses a limited ability to reset the cardiac pacemaker with temperature acclimation. Electrocardiogram recordings, taken from individual, anaesthetised zebrafish that had been acclimated to 18, 23 or 28°C were used to follow the response of maximum heart rate (fHmax ) to acute warming from 18°C until signs of cardiac failure appeared (up to c. 40°C). Because fHmax was similar across the acclimation groups at almost all equivalent test temperatures, warm acclimation was limited to one significant effect, the 23°C acclimated zebrafish had a significantly higher (21%) peak fHmax and reached a higher (3°C) test temperature than the 18°C acclimated zebrafish. Using zatebradine to block the membrane hyperpolarisation-activated cyclic nucleotide-gated channels (HCN) and examine the contribution of the membrane clock mechanisms to cardiac pacemaking, f Hmax was significantly reduced (by at least 40%) at all acute test temperatures and significantly more so at most test temperatures for zebrafish acclimated to 28°C vs. 23°C. Thus, HCN channels and the membrane clock were not only important, but could be modified by thermal acclimation. Using a combination of ryanodine (to block sarcoplasmic calcium release) and thapsigargin (to block sarcoplasmic calcium reuptake) to examine the contribution of sarcoplasmic reticular handling of calcium and the calcium clock, f Hmax was again consistently reduced independent of the test temperature and acclimation temperature, but to a significantly lesser degree than zatebradine for zebrafish acclimated to both 28 and 18°C. Thus, the calcium clock mechanism plays an additional role in setting pacemaker activity that was independent of temperature. In conclusion, the zebrafish cardiac pacemaker has a limited temperature acclimation ability compared with known effects for other fishes and involves two pacemaking mechanisms, one of which was independent of temperature.
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Affiliation(s)
- James L Marchant
- Zoology Department, University of British Columbia, Vancouver, British Columbia, Canada
| | - Anthony P Farrell
- Zoology Department, University of British Columbia, Vancouver, British Columbia, Canada
- Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada
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9
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Joyce W, Egginton S, Farrell AP, Axelsson M. Adrenergic and adenosinergic regulation of the cardiovascular system in an Antarctic icefish: Insight into central and peripheral determinants of cardiac output. Comp Biochem Physiol A Mol Integr Physiol 2019; 230:28-38. [DOI: 10.1016/j.cbpa.2018.12.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 12/19/2018] [Accepted: 12/19/2018] [Indexed: 01/27/2023]
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10
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Joyce W, White DW, Raven PB, Wang T. Weighing the evidence for using vascular conductance, not resistance, in comparative cardiovascular physiology. J Exp Biol 2019; 222:222/6/jeb197426. [DOI: 10.1242/jeb.197426] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
ABSTRACT
Vascular resistance and conductance are reciprocal indices of vascular tone that are often assumed to be interchangeable. However, in most animals in vivo, blood flow (i.e. cardiac output) typically varies much more than arterial blood pressure. When blood flow changes at a constant pressure, the relationship between conductance and blood flow is linear, whereas the relationship between resistance and blood flow is non-linear. Thus, for a given change in blood flow, the change in resistance depends on the starting point, whereas the attendant change in conductance is proportional to the change in blood flow regardless of the starting conditions. By comparing the effects of physical activity at different temperatures or between species – concepts at the heart of comparative cardiovascular physiology – we demonstrate that the difference between choosing resistance or conductance can be marked. We also explain here how the ratio of conductance in the pulmonary and systemic circulations provides a more intuitive description of cardiac shunt patterns in the reptilian cardiovascular system than the more commonly used ratio of resistance. Finally, we posit that, although the decision to use conductance or resistance should be made on a case-by-case basis, in most circumstances, conductance is a more faithful portrayal of cardiovascular regulation in vertebrates.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Daniel W. White
- School of Arts & Sciences, University of Houston-Victoria, Victoria, TX 77901, USA
| | - Peter B. Raven
- Department of Physiology and Anatomy, UNT Health Science Center, Fort Worth, TX 76107, USA
| | - Tobias Wang
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
- Aarhus Institute of Advanced Sciences (AIAS), Aarhus University, 8000 Aarhus C, Denmark
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11
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Joyce W, Axelsson M, Wang T. Contraction of atrial smooth muscle reduces cardiac output in perfused turtle hearts. ACTA ACUST UNITED AC 2019; 222:jeb.199828. [PMID: 30787139 DOI: 10.1242/jeb.199828] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Accepted: 02/18/2019] [Indexed: 11/20/2022]
Abstract
Unusual undulations in resting tension (tonus waves) were described in isolated atria from freshwater turtles more than a century ago. These tonus waves were soon after married with the histological demonstration of a rich layer of smooth muscle on the luminal side of the atrial wall. Research thereafter waned and the functional significance of this smooth muscle has remained obscure. Here, we provide evidence that contraction of the smooth muscle in the atria may be able to change cardiac output in turtle hearts. In in situ perfused hearts of the red-eared slider turtle (Trachemys scripta elegans), we demonstrated that activation of smooth muscle contraction with histamine (100 nmol kg-1 bolus injected into perfusate) reduced cardiac output by decreasing stroke volume (>50% decrease in both parameters). Conversely, inhibition of smooth muscle contraction with wortmannin (10 µmol l-1 perfusion) approximately doubled baseline stroke volume and cardiac output. We suggest that atrial smooth muscle provides a unique mechanism to control cardiac filling that could be involved in the regulation of stroke volume during diving.
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Affiliation(s)
- William Joyce
- Department of Bioscience, Section for Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Michael Axelsson
- Department of Biological and Environmental Sciences, University of Gothenburg, SE 405 30 Gothenburg, Sweden
| | - Tobias Wang
- Department of Bioscience, Section for Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark.,Aarhus Institute of Advanced Studies, Aarhus University, 8000 Aarhus C, Denmark
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12
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Joyce W, Egginton S, Farrell AP, Crockett EL, O'Brien KM, Axelsson M. Exploring nature's natural knockouts: in vivo cardiorespiratory performance of Antarctic fishes during acute warming. ACTA ACUST UNITED AC 2018; 221:jeb.183160. [PMID: 29967219 DOI: 10.1242/jeb.183160] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Accepted: 06/25/2018] [Indexed: 01/09/2023]
Abstract
We tested the hypothesis that blackfin icefish (Chaenocephalus aceratus), one of the six species in the family Channichthyidae (the icefishes) that do not express haemoglobin and myoglobin, lack regulatory cardiovascular flexibility during acute warming and activity. The experimental protocols were designed to optimize the surgical protocol and minimize stress. First, minimally invasive heart rate (fH) measurements were made during a thermal ramp until cardiac failure in C. aceratus and compared with those from the closely related red-blooded black rockcod (Notothenia coriiceps). Then, integrative cardiovascular adjustments were more extensively studied using flow probes and intravascular catheters in C. aceratus during acute warming (from 0 to 8°C) at rest and after imposed activity. Chaenocephalus aceratus had a lower routine fH than N. coriiceps (9 beats min-1 versus 14 beats min-1) and a lower peak fH during acute warming (38 beats min-1 versus 55 beats min-1) with a similar cardiac breakpoint temperature (13 and 14°C, respectively). Routine cardiac output (Q̇) for C. aceratus at ∼0°C was much lower (26.6 ml min-1 kg-1) than previously reported, probably because fish in the present study had a low fH (12 beats min-1) indicative of a high routine vagal tone and low stress. Chaenocephalus aceratus increased oxygen consumption during acute warming and with activity. Correspondingly, Q̇ increased considerably (maximally 86.3 ml min-1 kg-1), as did vascular conductance (5-fold). Thus, unlike earlier suggestions, these data provide convincing evidence that icefish can mount a well-developed cardiovascular regulation of heart rate, cardiac output and vascular conductance, and this regulatory capacity provides flexibility during acute warming.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Stuart Egginton
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
| | - Anthony P Farrell
- Department of Zoology, and Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC 45, Canada
| | | | - Kristin M O'Brien
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA
| | - Michael Axelsson
- Department of Biological and Environmental Sciences, University of Gothenburg, 4139 90 Gothenburg, Sweden
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13
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Joyce W, Elsey RM, Wang T, Crossley DA. Maximum heart rate does not limit cardiac output at rest or during exercise in the American alligator (Alligator mississippiensis). Am J Physiol Regul Integr Comp Physiol 2018; 315:R296-R302. [DOI: 10.1152/ajpregu.00027.2018] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In most vertebrates, increases in cardiac output result from increases in heart rate (fH) with little or no change in stroke volume (Vs), and maximum cardiac output (Q̇) is typically attained at or close to maximum fH. We therefore tested the hypothesis that increasing maximum fH may increase maximum Q̇. To this end, we investigated the effects of elevating fH with right atrial pacing on Q̇ in the American alligator ( Alligator mississippiensis) at rest and while swimming. During normal swimming, Q̇ increased entirely by virtue of a tachycardia (29 ± 1 to 40 ± 3 beats/min), whereas Vs remained stable. In both resting and swimming alligators, increasing fH with right atrial pacing resulted in a parallel decline in Vs that resulted in an unchanged cardiac output. In swimming animals, this reciprocal relationship extended to supraphysiological fH (up to ~72 beats/min), which suggests that maximum fH does not limit maximum cardiac output and that fH changes are secondary to the peripheral factors (for example vascular capacitance) that determine venous return at rest and during exercise.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, Aarhus, Denmark
| | - Ruth M. Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, Louisiana
| | - Tobias Wang
- Department of Zoophysiology, Aarhus University, Aarhus, Denmark
- Aarhus Institute of Advanced Studies, Aarhus University, Aarhus, Denmark
| | - Dane A. Crossley
- Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, Texas
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Joyce W, Crossley J, Elsey RM, Wang T, Crossley DA. Contribution of active atrial contraction to cardiac output in anesthetized American alligators ( Alligator mississippiensis). ACTA ACUST UNITED AC 2018; 221:jeb.178194. [PMID: 29615521 DOI: 10.1242/jeb.178194] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 03/21/2018] [Indexed: 12/30/2022]
Abstract
Ventricular filling may occur directly from the venous circulation during early diastole or via atrial contraction in late diastole. The contribution of atrial contraction to ventricular filling is typically small in mammals (10-40%), but has been suggested to predominate in reptiles. We investigated the importance of atrial contraction in filling of the ventricle in American alligators (Alligator mississippiensis) by bypassing both atria (with the use of ligatures to prevent atrial filling) and measuring the resultant effects on cardiac output in anesthetized animals. Atrial ligation had no significant effects on total systemic blood flow before or after adrenaline injection. Unexpectedly, pulmonary flow was increased following atrial ligation prior to adrenaline treatment, but was unaffected after it. These findings suggest that the atria are non-essential (i.e. redundant) for ventricular filling in alligators, at least under anesthesia, but may serve as important volume reservoirs.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Janna Crossley
- Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, TX 76203-5017, USA
| | - Ruth M Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA 70643, USA
| | - Tobias Wang
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark.,Aarhus Institute of Advanced Studies, Aarhus University, 8000 Aarhus C, Denmark
| | - Dane A Crossley
- Department of Biological Sciences, Developmental Integrative Biology Cluster, University of North Texas, Denton, TX 76203-5017, USA
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Joyce W, Axelsson M, Egginton S, Farrell AP, Crockett EL, O’Brien KM. The effects of thermal acclimation on cardio-respiratory performance in an Antarctic fish ( Notothenia coriiceps). CONSERVATION PHYSIOLOGY 2018; 6:coy069. [PMID: 30568798 PMCID: PMC6291619 DOI: 10.1093/conphys/coy069] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 11/13/2018] [Accepted: 11/26/2018] [Indexed: 05/21/2023]
Abstract
The Southern Ocean has experienced stable, cold temperatures for over 10 million years, yet particular regions are currently undergoing rapid warming. To investigate the impacts of warming on cardiovascular oxygen transport, we compared the cardio-respiratory performance in an Antarctic notothenioid (Notothenia coriiceps) that was maintained at 0 or 5°C for 6.0-9.5 weeks. When compared at the fish's respective acclimation temperature, the oxygen consumption rate and cardiac output were significantly higher in 5°C-acclimated than 0°C-acclimated fish. The 2.7-fold elevation in cardiac output in 5°C-acclimated fish (17.4 vs. 6.5 ml min-1 kg-1) was predominantly due to a doubling of stroke volume, likely in response to increased cardiac preload, as measured by higher central venous pressure (0.15 vs. 0.08 kPa); tachycardia was minor (29.5 vs. 25.2 beats min-1). When fish were acutely warmed, oxygen consumption rate increased by similar amounts in 0°C- and 5°C-acclimated fish at equivalent test temperatures. In both acclimation groups, the increases in oxygen consumption rate during acute heating were supported by increased cardiac output achieved by elevating heart rate, while stroke volume changed relatively little. Cardiac output was similar between both acclimation groups until 12°C when cardiac output became significantly higher in 5°C-acclimated fish, driven largely by their higher stroke volume. Although cardiac arrhythmias developed at a similar temperature (~14.5°C) in both acclimation groups, the hearts of 5°C-acclimated fish continued to pump until significantly higher temperatures (CTmax for cardiac function 17.7 vs. 15.0°C for 0°C-acclimated fish). These results demonstrate that N. coriiceps is capable of increasing routine cardiac output during both acute and chronic warming, although the mechanisms are different (heart rate-dependent versus primarily stroke volume-dependent regulation, respectively). Cardiac performance was enhanced at higher temperatures following 5°C acclimation, suggesting cardiovascular function may not constrain the capacity of N. coriiceps to withstand a warming climate.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, Aarhus C, Denmark
- Corresponding author: Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark.
| | - Michael Axelsson
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
| | - Stuart Egginton
- School of Biomedical Sciences, University of Leeds, Leeds, UK
| | - Anthony P Farrell
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada
| | | | - Kristin M O’Brien
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
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16
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Venous pressures and cardiac filling in turtles during apnoea and intermittent ventilation. J Comp Physiol B 2017; 188:481-490. [DOI: 10.1007/s00360-017-1132-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Revised: 10/01/2017] [Accepted: 10/15/2017] [Indexed: 10/18/2022]
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17
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18
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Brijs J, Sandblom E, Dekens E, Näslund J, Ekström A, Axelsson M. Cardiac remodeling and increased central venous pressure underlie elevated stroke volume and cardiac output of seawater-acclimated rainbow trout. Am J Physiol Regul Integr Comp Physiol 2017; 312:R31-R39. [DOI: 10.1152/ajpregu.00374.2016] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Revised: 10/11/2016] [Accepted: 11/23/2016] [Indexed: 11/22/2022]
Abstract
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 increase from 10 to 16.5°C, both acclimation groups exhibited similar increases in heart rate (Q10 of ~2), but SV tended to decrease in seawater-acclimated trout despite the fact that CVP was maintained in both groups. This resulted in CO of seawater- and freshwater-acclimated trout stabilizing at a similar level after warming (~26 ml·min−1·kg−1). The consistently higher CVP of seawater-acclimated trout suggests that factors other than compromised cardiac filling constrained the SV and CO of these individuals at high temperatures. The present study highlights, for the first time, the complex interacting effects of temperature and water salinity on cardiovascular responses in a euryhaline fish species.
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Affiliation(s)
- Jeroen Brijs
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
| | - Erik Sandblom
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
| | - Esmée Dekens
- Institute for Life Sciences and Chemistry, University of Applied Sciences, Utrecht, The Netherlands; and
| | - Joacim Näslund
- Faculty of Science, Department of Ecosystem Biology, University of South Bohemia, České Budějovice, Czech Republic
| | - Andreas Ekström
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
| | - Michael Axelsson
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
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Abramochkin DV, Vornanen M. Seasonal changes of cholinergic response in the atrium of Arctic navaga cod (Eleginus navaga). J Comp Physiol B 2016; 187:329-338. [PMID: 27672043 DOI: 10.1007/s00360-016-1032-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2016] [Revised: 08/26/2016] [Accepted: 09/13/2016] [Indexed: 11/24/2022]
Abstract
Fishes of north-temperate latitudes exhibit marked seasonal changes in electrical excitability of the heart partly as an outcome of temperature-dependent changes in the density of major K+ ion currents: delayed rectifiers (IKr, IKs) and background inward rectifier (IK1). In the arctic teleost, navaga cod (Eleginus navaga), IKr and IK1 are strongly up-regulated in winter. The current study tests the hypothesis that the ligand-gated K+ current, the acetylcholine-activated inward rectifier, IKACh, is also modified by seasonal acclimatization in atrial myocytes of navaga. In sinoatrial preparations of the summer-acclimatized (SA) navaga, 10-6 M carbamylcholine chloride (CCh) caused slowing of heart rate, shortening of atrial action potential (AP) duration and a drastic reduction of AP amplitude, eventually resulting in inexcitability. In winter-acclimatized (WA) atria CCh slowed HR and reduced AP duration, but reduction of AP amplitude was modest and never resulted in inexcitability. The difference in cholinergic response between SA and WA navaga is explained by seasonal changes in IKACh density. The peak density of IKACh, induced by 10-5 M CCh, at the common experimental temperature (+6 °C) was 0.97 ± 0.28 pA/pF in SA navaga but only 0.183 ± 0.013 pA/pF in WA navaga (a 5.3-fold difference, P < 0.05). At acclimatization temperatures of the fish IKACh density was 2.8 ± 0.50 (at +12 °C) and 0.11 ± 0.06 pA/pF (at +3 °C) (a 26-fold difference, P < 0.05) for SA and WA navaga, respectively. Thus, acclimatization to summer induces a drastic up-regulation of the atrial IKACh, which effectively shortens atrial AP. The reverse temperature compensation of the atrial IKACh may be advantageous in summer under variable water temperatures and oxygen concentrations by reducing workload of the heart.
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Affiliation(s)
- Denis V Abramochkin
- Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye Gory, 1, 12, Moscow, Russia. .,Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russia.
| | - Matti Vornanen
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
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Lee L, Genge CE, Cua M, Sheng X, Rayani K, Beg MF, Sarunic MV, Tibbits GF. Functional Assessment of Cardiac Responses of Adult Zebrafish (Danio rerio) to Acute and Chronic Temperature Change Using High-Resolution Echocardiography. PLoS One 2016; 11:e0145163. [PMID: 26730947 PMCID: PMC4701665 DOI: 10.1371/journal.pone.0145163] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Accepted: 11/27/2015] [Indexed: 12/21/2022] Open
Abstract
The zebrafish (Danio rerio) is an important organism as a model for understanding vertebrate cardiovascular development. However, little is known about adult ZF cardiac function and how contractile function changes to cope with fluctuations in ambient temperature. The goals of this study were to: 1) determine if high resolution echocardiography (HRE) in the presence of reduced cardiodepressant anesthetics could be used to accurately investigate the structural and functional properties of the ZF heart and 2) if the effect of ambient temperature changes both acutely and chronically could be determined non-invasively using HRE in vivo. Heart rate (HR) appears to be the critical factor in modifying cardiac output (CO) with ambient temperature fluctuation as it increases from 78 ± 5.9 bpm at 18°C to 162 ± 9.7 bpm at 28°C regardless of acclimation state (cold acclimated CA- 18°C; warm acclimated WA- 28°C). Stroke volume (SV) is highest when the ambient temperature matches the acclimation temperature, though this difference did not constitute a significant effect (CA 1.17 ± 0.15 μL at 18°C vs 1.06 ± 0.14 μl at 28°C; WA 1.10 ± 0.13 μL at 18°C vs 1.12 ± 0.12 μl at 28°C). The isovolumetric contraction time (IVCT) was significantly shorter in CA fish at 18°C. The CA group showed improved systolic function at 18°C in comparison to the WA group with significant increases in both ejection fraction and fractional shortening and decreases in IVCT. The decreased early peak (E) velocity and early peak velocity / atrial peak velocity (E/A) ratio in the CA group are likely associated with increased reliance on atrial contraction for ventricular filling.
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Affiliation(s)
- Ling Lee
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Child and Family Research Institute, Department of Cardiovascular Science, 950 West 28th Ave, Vancouver, BC V5Z 4H4, Canada
| | - Christine E. Genge
- Child and Family Research Institute, Department of Cardiovascular Science, 950 West 28th Ave, Vancouver, BC V5Z 4H4, Canada
| | - Michelle Cua
- School of Engineering Science, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Xiaoye Sheng
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Child and Family Research Institute, Department of Cardiovascular Science, 950 West 28th Ave, Vancouver, BC V5Z 4H4, Canada
| | - Kaveh Rayani
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Mirza F. Beg
- School of Engineering Science, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Marinko V. Sarunic
- School of Engineering Science, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Glen F. Tibbits
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Child and Family Research Institute, Department of Cardiovascular Science, 950 West 28th Ave, Vancouver, BC V5Z 4H4, Canada
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Joyce W, Axelsson M, Wang T. Autoregulation of cardiac output is overcome by adrenergic stimulation in the anaconda heart. J Exp Biol 2016; 220:336-340. [DOI: 10.1242/jeb.149237] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 11/03/2016] [Indexed: 11/20/2022]
Abstract
Most vertebrates increase cardiac output during activity by elevating heart rate with relatively stable stroke volume. However, several studies have demonstrated ‘intrinsic autoregulation’ of cardiac output where artificially increased heart rate is associated with decreased stroke volume, leaving cardiac output unchanged. We explored the capacity of noradrenaline to overcome autoregulation in the anaconda heart. Electrically pacing in situ perfused hearts from the intrinsic heart rate to the maximum attainable resulted in a proportional decrease in stroke volume. However, noradrenaline, which increased heart rate to the same frequency as pacing, maintained stroke volume and thus increased cardiac output. In atrial and ventricular preparations noradrenaline significantly increased the force of contraction and contraction kinetics. Thus, the increased contractility associated with adrenergic stimulation ameliorates filling limitations at high heart rates. Although heart rate appears the primary regulated variable during activity, this may only be achieved with compensatory amendments in myocardial contractility provided by adrenergic stimulation.
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Affiliation(s)
- William Joyce
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
| | - Michael Axelsson
- Department of Biological and Environmental Sciences, University of Gothenburg, 405 30 Gothenburg, Sweden
| | - Tobias Wang
- Department of Zoophysiology, Aarhus University, 8000 Aarhus C, Denmark
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22
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Joyce W, Simonsen M, Gesser H, Wang T. The effects of hypoxic bradycardia and extracellular HCO3−/CO2 on hypoxic performance in the eel heart. J Exp Biol 2015; 219:302-5. [DOI: 10.1242/jeb.130971] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 11/16/2015] [Indexed: 10/22/2022]
Abstract
During hypoxia fishes exhibit a characteristic ‘hypoxic bradycardia’, the functional significance of which remains debated. Here, we investigated the hypothesis that hypoxic bradycardia primarily safeguards cardiac performance. In preparations from the European eel (Anguilla anguilla), a decrease in stimulation frequency from 40 to 15 beats per minute, which replicates hypoxic bradycardia in vivo, vastly improved cardiac performance during hypoxia in vitro. As eels display dramatic shifts in extracellular HCO3−/CO2, we further investigated the effect this has upon hypoxic cardiac performance. Elevations from 10 mM HCO3−/ 1% to 40 mM HCO3−/ 4% CO2 had few effects on performance, however further, but still physiologically relevant, increases to 70 mM HCO3−/ 7% CO2 compromised hypoxia tolerance. We revealed a four-way interaction between HCO3−/CO2, contraction frequency, hypoxia and performance over time, whereby the benefit of hypoxic bradycardia was most prolonged at 10 mM HCO3−/ 1% CO2. Together, our data suggest that hypoxic bradycardia greatly benefits cardiac performance, but its significance may be context-specific.
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Affiliation(s)
- William Joyce
- Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, Universitetsparken, 8000 Aarhus C, Denmark
| | - Maj Simonsen
- Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, Universitetsparken, 8000 Aarhus C, Denmark
| | - Hans Gesser
- Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, Universitetsparken, 8000 Aarhus C, Denmark
| | - Tobias Wang
- Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, Universitetsparken, 8000 Aarhus C, Denmark
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23
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Ekström A, Jutfelt F, Sandblom E. Effects of autonomic blockade on acute thermal tolerance and cardioventilatory performance in rainbow trout, Oncorhynchus mykiss. J Therm Biol 2014; 44:47-54. [PMID: 25086973 DOI: 10.1016/j.jtherbio.2014.06.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 05/30/2014] [Accepted: 06/02/2014] [Indexed: 10/25/2022]
Abstract
Predicted future increases in global temperature may impose challenges for ectothermic animals like fish, but the physiological mechanisms determining the critical thermal maximum (CTmax) are not well understood. One hypothesis suggests that impaired cardiac performance, limited by oxygen supply, is an important underlying mechanism. Since vagal bradycardia is suggested to improve cardiac oxygenation and adrenergic stimulation may improve cardiac contractility and protect cardiac function at high temperatures, we predicted that pharmacological blockade of cardiac autonomic control would lower CTmax. Rainbow trout was instrumented with a flow probe and a ventilation catheter for cardioventilatory recordings and exposed to an acute thermal challenge until CTmax following selective pharmacological blockade of muscarinic or β-adrenergic receptors. Contrary to our prediction, CTmax (~26°C) was unchanged between treatments. While β-adrenergic blockade reduced heart rate it did not impair cardiac stroke volume across temperatures suggesting that compensatory increases in cardiac filling pressure may serve to maintain cardiac output. While warming resulted in significant tachycardia and increased cardiac output, a high cholinergic tone on the heart was observed at temperatures approaching CTmax. This may represent a mechanism to maintain scope for heart rate and possibly to improve myocardial contractility and oxygen supply at high temperatures. This is the first study evaluating the importance of autonomic cardiac control on thermal tolerance in fish. While no effects on CTmax were observed, this study raises important questions about the underlying mechanisms determining thermal tolerance limits in ectothermic animals.
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Affiliation(s)
- Andreas Ekström
- Department of Biology and Environmental Sciences, University of Gothenburg, Gothenburg Sweden.
| | - Fredrik Jutfelt
- Department of Biology and Environmental Sciences, University of Gothenburg, Gothenburg Sweden; The Sven Lovén Centre for Marine Sciences, Kristineberg, Fiskebäckskil, Sweden
| | - Erik Sandblom
- Department of Biology and Environmental Sciences, University of Gothenburg, Gothenburg Sweden
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24
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Marks C, Eme J, Elsey RM, Crossley DA. Chronic hypoxic incubation blunts thermally dependent cholinergic tone on the cardiovascular system in embryonic American alligator (Alligator mississippiensis). J Comp Physiol B 2013; 183:947-57. [DOI: 10.1007/s00360-013-0755-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2013] [Revised: 03/04/2013] [Accepted: 03/15/2013] [Indexed: 11/29/2022]
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25
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Keen A, Gamperl AK. Blood oxygenation and cardiorespiratory function in steelhead trout (Oncorhynchus mykiss) challenged with an acute temperature increase and zatebradine-induced bradycardia. J Therm Biol 2012. [DOI: 10.1016/j.jtherbio.2012.01.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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26
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Elevated temperature, per se, does not limit the ability of rainbow trout to increase stroke volume. J Therm Biol 2011. [DOI: 10.1016/j.jtherbio.2010.08.007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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27
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Yoshida M, Hirano R, Shima T. Photocardiography: a novel method for monitoring cardiac activity in fish. Zoolog Sci 2009; 26:356-61. [PMID: 19715506 DOI: 10.2108/zsj.26.356] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A non-invasive technique to monitor cardiac activity in small fish, such as goldfish, zebrafish, and medaka, is needed. In the present study, we developed photocardiography (PCG), a non-invasive optical method, to record cardiac activity in small fish. The method monitors changes in near-infrared light transmission through the heart using a phototransistor located outside the body. With this technique, heartbeats in fish of various sizes (14-218 mm) were stably recorded. PCG was applied to monitor the heartbeat during fear-related classical heart rate conditioning in goldfish wherein an electrical shock was used as an unconditioned stimulus. The heartbeats were continuously monitored, even when the beat coincided with the electrical shock, showing that PCG is robust even in an electrically noisy environment. This technique is particularly useful when monitoring the heartbeats of fish of small size or in the presence of ambient electrical noise, conditions in which the use of conventional electrocardiography (ECG) is difficult.
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Affiliation(s)
- Masayuki Yoshida
- Graduate School of Biosphere Science, Hiroshima University, Higashihiroshima, Hiroshima, Japan.
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28
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Sandblom E, Cox GK, Perry SF, Farrell AP. The role of venous capacitance, circulating catecholamines, and heart rate in the hemodynamic response to increased temperature and hypoxia in the dogfish. Am J Physiol Regul Integr Comp Physiol 2009; 296:R1547-56. [DOI: 10.1152/ajpregu.90961.2008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hypoxia and increased temperature alter venous blood pressures in teleosts through active changes in venous tone. Elasmobranchs possess a capacious venous system but have limited adrenergic vascular innervation and subambient central venous pressure (Pcv). In this study, we explored venous hemodynamic responses to acute temperature increase and moderate (6.9 kPa) and severe (2.5 kPa) hypoxia in the dogfish ( Squalus acanthias). Normoxic dogfish at 10°C had a Pcv between −0.08 and −0.04 kPa and a mean circulatory filling pressure (Pmcf) of ∼0.12 kPa. At 16°C, heart rate ( fH), cardiac output (Q), and Pmcf increased but Pcv and plasma epinephrine and norepinephrine levels were unchanged. In contrast, moderate and severe hypoxia increased Pcv and decreased Q and stroke volume (VS). fH decreased in severe hypoxia, whereas Pmcf was unaffected despite elevated catecholamine levels. Atropine abolished hypoxic reductions in Q, VS, and fH, but Pcv still increased. In contrast to the response in teleosts, this study on dogfish suggests that venous capacitance changes associated with warming and hypoxia are minimal and likely not mediated by circulating catecholamines. Thus hemodynamic status of the capacious elasmobranch venous circulation is potentially regulated by blood volume shifts from passive flow-mediated events and possibly through myogenic mechanisms.
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30
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Clark TD, Sandblom E, Cox GK, Hinch SG, Farrell AP. Circulatory limits to oxygen supply during an acute temperature increase in the Chinook salmon (Oncorhynchus tshawytscha). Am J Physiol Regul Integr Comp Physiol 2008; 295:R1631-9. [PMID: 18768764 DOI: 10.1152/ajpregu.90461.2008] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study was undertaken to provide a comprehensive set of data relevant to disclosing the physiological effects and possible oxygen transport limitations in the Chinook salmon (Oncorhynchus tshawytscha) during an acute temperature change. Fish were instrumented with a blood flow probe around the ventral aorta and catheters in the dorsal aorta and sinus venosus. Water temperature was progressively increased from 13 degrees C in steps of 4 degrees C up to 25 degrees C. Cardiac output increased from 29 to 56 ml.min(-1).kg(-1) between 13 and 25 degrees C through an increase in heart rate (58 to 105 beats/min). Systemic vascular resistance was reduced, causing a stable dorsal aortic blood pressure, yet central venous blood pressure increased significantly at 25 degrees C. Oxygen consumption rate increased from 3.4 to 8.7 mg.min(-1).kg(-1) during the temperature increase, although there were signs of anaerobic respiration at 25 degrees C in the form of increased blood lactate and decreased pH. Arterial oxygen partial pressure was maintained during the heat stress, although venous oxygen partial pressure (Pv(O(2))) and venous oxygen content were significantly reduced. Cardiac arrhythmias were prominent in three of the largest fish (>4 kg) at 25 degrees C. Given the switch to anaerobic metabolism and the observation of cardiac arrhythmias at 25 degrees C, we propose that the cascade of venous oxygen depletion results in a threshold value for Pv(O(2)) of around 1 kPa. At this point, the oxygen supply to systemic and cardiac tissues is compromised, such that the oxygen-deprived and acidotic myocardium becomes arrhythmic, and blood perfusion through the gills and to the tissues becomes compromised.
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Affiliation(s)
- Timothy D Clark
- Faculty of Land and Food Systems, Univ. of British Columbia, Vancouver, Canada, V6T 1Z4.
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31
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Cotter PA, Han AJ, Everson JJ, Rodnick KJ. Cardiac hemodynamics of the rainbow trout (Oncorhynchus mykiss) using simultaneous Doppler echocardiography and electrocardiography. ACTA ACUST UNITED AC 2008; 309:243-54. [PMID: 18366108 DOI: 10.1002/jez.453] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Using Doppler echocardiography and electrocardiography, we characterized cardiac hemodynamics, timing, and electromechanical function, and examined the effects of ventricular hypertrophy on systolic function in anesthetized rainbow trout. Atrial filling (D(SA)), ventricular filling (D(AV)), and ventricular ejection (D(VB)) accounted for 40-77, 13-27, and 22-41% of the cardiac cycle, respectively. Ventricular ejection occurred entirely during atrial filling and ended by the time the QT interval was 80% (SD=9%) completed. Sinoatrial (SA) flow was of longer duration (0.53+/-0.08 sec, mean+/-SD) and lower velocity (32+/-8 cm sec(-1)) than corresponding atrioventricular (AV, 0.19+/-0.02 sec; 87+/-8 cm sec(-1)) and ventriculobulbar (VB, 0.30+/-0.05 sec; 63+/-20 cm sec(-1)) values. Despite a wide range of heart masses, atrioventricular and VB valve dimensions were identical ( approximately 5.5 mm(2)). Ventricle mass (M(V)), but not relative ventricle mass (RVM), and cardiac cycle length were positively correlated (r(2)=0.57, P<0.001); thus, all time-dependent electrical/mechanical measures of cardiac function were significantly related to M(V), but not RVM. All rate-corrected (c) electromechanical event durations (except cD(SA)) and the systolic function index (cPEP (pre-ejection period)/D(VB)) were independent of RVM, suggesting the maintenance of cardiac functional capabilities across maturation stages (males) and different ventricle sizes (males and females). In summary, we define fundamental electrical and mechanical properties of the in vivo teleost myocardium under anesthesia, and report the maintenance of systolic function over a wide range of heart sizes for both sexes and maturation state of males. We also suggest that the short duration of ventricular emptying relative to the QT interval may provide a novel mechanism to adjust stroke volume and cardiac output in teleosts.
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Affiliation(s)
- Paul A Cotter
- Department of Biological Sciences, Idaho State University, Pocatello, Idaho, USA.
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Enforced exercise, but not acute temperature elevation, decreases venous capacitance in the stenothermal Antarctic fish Pagothenia borchgrevinki. J Comp Physiol B 2008; 178:845-51. [DOI: 10.1007/s00360-008-0272-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Revised: 04/24/2008] [Accepted: 05/05/2008] [Indexed: 11/25/2022]
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Sandblom E, Axelsson M. The venous circulation: a piscine perspective. Comp Biochem Physiol A Mol Integr Physiol 2007; 148:785-801. [PMID: 17920321 DOI: 10.1016/j.cbpa.2007.08.036] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2007] [Revised: 08/31/2007] [Accepted: 08/31/2007] [Indexed: 11/27/2022]
Abstract
Vascular capacitance describes the pressure-volume relationship of the circulatory system. The venous vasculature, which is the main capacitive region in the circulation, is actively controlled by various neurohumoral systems. In terrestrial animals, vascular capacitance control is crucial to prevent orthostatic blood pooling in dependent limbs, while in aquatic animals like fish, the effects of gravity are cancelled out by hydrostatic forces making orthostatic blood pooling an unlikely concern for these animals. Nevertheless, changes in venous capacitance have important implications on cardiovascular homeostasis in fish since it affects venous return and cardiac filling pressure (i.e. central venous blood pressure), which in turn may affect cardiac output. The mean circulatory filling pressure is used to estimate vascular capacitance. In unanaesthetized animals, it is measured as the central venous plateau pressure during a transient stoppage of cardiac output. So far, most studies of venous function in fish have addressed the situation in teleosts (notably the rainbow trout, Oncorhynchus mykiss), while any information on elasmobranchs, cyclostomes and air-breathing fishes is more limited. This review describes venous haemodynamic concepts and neurohumoral control systems in fish. Particular emphasis is placed on venous responses to natural cardiovascular challenges such as exercise, environmental hypoxia and temperature changes.
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Affiliation(s)
- Erik Sandblom
- Department of Zoology, Göteborg University, Box 463, S-405 30 Gothenburg, Sweden.
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Sandblom E, Axelsson M. Venous hemodynamic responses to acute temperature increase in the rainbow trout (Oncorhynchus mykiss). Am J Physiol Regul Integr Comp Physiol 2007; 292:R2292-8. [PMID: 17322113 DOI: 10.1152/ajpregu.00884.2006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Many ectotherms regularly experience considerable short-term variations in environmental temperature, which affects their body temperature. Here we investigate the cardiovascular responses to a stepwise acute temperature increase from 10 to 13 and 16°C in rainbow trout ( Oncorhynchus mykiss). Cardiac output increased by 20 and 31% at 13 and 16°C, respectively. This increase was entirely mediated by an increased heart rate (fH), whereas stroke volume (SV) decreased significantly by 20% at 16°C. The mean circulatory filling pressure (MCFP), a measure of venous capacitance, increased with temperature. Central venous pressure (Pven) did not change, whereas the pressure gradient for venous return (MCFP-Pven) was significantly increased at both 13 and 16°C. Blood volume, as measured by the dilution of51Cr-labeled red blood cells, was temperature insensitive in both intact and splenectomized trout. This study demonstrates that venous capacitance in trout decreases, but cardiac filling pressure as estimated by Pvendoes not change when cardiac output increases during an acute temperature increase. SV was compromised as fHincreased with temperature. The decreased capacitance likely serves to prevent passive pooling of blood in the venous periphery and to maintain cardiac filling pressure and a favorable pressure gradient for venous return.
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Affiliation(s)
- Erik Sandblom
- Department of Zoology, Göteborg University, Göteborg, Sweden.
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Larsson DGJ, Fredriksson S, Sandblom E, Paxeus N, Axelsson M. Is heart rate in fish a sensitive indicator to evaluate acute effects of β-blockers in surface water? ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2006; 22:338-340. [PMID: 21783729 DOI: 10.1016/j.etap.2006.05.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2006] [Revised: 05/05/2006] [Accepted: 05/07/2006] [Indexed: 05/31/2023]
Abstract
We have investigated if propranolol, a non-selective β-blocker present in sewage effluents, affects heart rate in rainbow trout. During a 48h exposure to a very high concentration of propranolol (70.9μg/L) no effects on heart rate were found. After a subsequent intravenous injection of propranolol, heart rate remained unaffected in pre-exposed fish but was significantly lowered in naïve fish. Other studies have reported effects on the reproduction of fish by propranolol dissolved in water at much lower concentrations. The present study suggests that physiological systems under homeostatic control, like heart rate, may not be particularly sensitive despite being direct targets.
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Affiliation(s)
- D G Joakim Larsson
- The Institute for Neuroscience and Physiology, Department of Physiology/Endocrinology, the Sahlgrenska Academy at Göteborg University, Box 434, SE-405 30 Göteborg, Sweden
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Sandblom E, Axelsson M, Farrell AP. Central venous pressure and mean circulatory filling pressure in the dogfishSqualus acanthias: adrenergic control and role of the pericardium. Am J Physiol Regul Integr Comp Physiol 2006; 291:R1465-73. [PMID: 16825417 DOI: 10.1152/ajpregu.00282.2006] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Subambient central venous pressure (Pven) and modulation of venous return through cardiac suction (vis a fronte) characterizes the venous circulation in sharks. Venous capacitance was estimated in the dogfish S qualus acanthias by measuring the mean circulatory filling pressure (MCFP) during transient occlusion of cardiac outflow. We tested the hypothesis that venous return and cardiac preload can be altered additionally through adrenergic changes of venous capacitance. The experiments involved the surgical opening of the pericardium to place a perivascular occluder around the conus arteriosus. Another control group was identically instrumented, but lacked the occluder, and was subjected to the same pharmacological protocol to evaluate how pericardioectomy affected cardiovascular status. Routine Pvenwas negative (−0.08 ± 0.02 kPa) in control fish but positive (0.09 ± 0.01 kPa) in the pericardioectomized group. Injections of 5 μg/kg body mass ( Mb) of epinephrine and phenylephrine (100 μg/kg Mb) increased Pvenand MCFP, whereas isoproterenol (1 μg/kg Mb) decreased both variables. Thus, constriction and relaxation of the venous vasculature were mediated through the respective stimulation of α- and β-adrenergic receptors. α-Adrenergic blockade with prazosin (1 mg/kg Mb) attenuated the responses to phenylephrine and decreased resting Pvenin pericardioectomized animals. Our results provide convincing evidence for adrenergic control of the venous vasculature in elasmobranchs, although the pericardium is clearly an important component in the modulation of venous function. Thus active changes in venous capacitance have previously been underestimated as an important means of modulating venous return and cardiac performance in this group.
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Affiliation(s)
- Erik Sandblom
- Dept. of Zoology, Göteborg Univ., Box 463, Göteborg S-405 30, Sweden.
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Skals M, Skovgaard N, Taylor EW, Leite CAC, Abe AS, Wang T. Cardiovascular changes under normoxic and hypoxic conditions in the air-breathing teleostSynbranchus marmoratus: importance of the venous system. J Exp Biol 2006; 209:4167-73. [PMID: 17023609 DOI: 10.1242/jeb.02459] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYSynbranchus marmoratus is a facultative air-breathing fish, which uses its buccal cavity as well as its gills for air-breathing. S. marmoratus shows a very pronounced tachycardia when it surfaces to air-breathe. An elevation of heart rate decreases cardiac filling time and therefore may cause a decline in stroke volume (VS), but this can be compensated for by an increase in venous tone to maintain stroke volume. Thus, the study on S. marmoratus was undertaken to investigate how stroke volume and venous function are affected during air-breathing. To this end we measured cardiac output(Q̇), heart rate(fH), central venous blood pressure(PCV), mean circulatory filling pressure (MCFP), and dorsal aortic blood pressures (PDA) in S. marmoratus. Measurements were performed in aerated water(PO2>130 mmHg), when the fish alternated between gill ventilation and prolonged periods of apnoeas, as well as during hypoxia(PO2≤50 mmHg), when the fish changed from gill ventilation to air-breathing. Q̇increased significantly during gill ventilation compared to apnoea in aerated water through a significant increase in both fH and VS. PCV and MCFP also increased significantly. During hypoxia, when the animals surface to ventilate air, we found a marked rise in fH, PCV, MCFP, Q̇ and VS, whereas PDA decreased significantly. Simultaneous increases in PCV and MCFP in aerated, as well as in hypoxic water,suggests that the venous system plays an important regulatory role for cardiac filling and VS in this species. In addition, we investigated adrenergic regulation of the venous system through bolus infusions of adrenergic agonists (adrenaline, phenylephrine and isoproterenol;2 μg kg–1). Adrenaline and phenylephrine caused a marked rise in PCV and MCFP, whereas isoproterenol led to a marked decrease in PCV, and tended to decrease MCFP. Thus,it is evident that stimulation of both α- and β-adrenoreceptors affects venous tone in S. marmoratus.
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Affiliation(s)
- Marianne Skals
- Zoophysiology, Department of Biological Sciences, University of Aarhus, 8000 Aarhus, Denmark.
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Sandblom E, Axelsson M, McKenzie DJ. Venous responses during exercise in rainbow trout, Oncorhynchus mykiss: α-adrenergic control and the antihypotensive function of the renin–angiotensin system. Comp Biochem Physiol A Mol Integr Physiol 2006; 144:401-9. [PMID: 16730467 DOI: 10.1016/j.cbpa.2006.03.003] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2006] [Revised: 03/06/2006] [Accepted: 03/07/2006] [Indexed: 11/22/2022]
Abstract
The role of the alpha-adrenergic system in the control of cardiac preload (central venous blood pressure; P(ven)) and venous capacitance during exercise was investigated in rainbow trout (Oncorhynchus mykiss). In addition, the antihypotensive effect of the renin-angiotesin system (RAS) was investigated during exercise after alpha-adrenoceptor blockade. Fish were subjected to a 20-min exercise challenge at 0.66 body lengths s(-1) (BL s(-1)) while P(ven), dorsal aortic blood pressure (P(da)) and relative cardiac output (Q) was recorded continuously. Heart rate (f(H)), cardiac stroke volume (SV) and total systemic resistance (R(sys)) were derived from these variables. The mean circulatory filling pressure (MCFP) was measured at rest and at the end of the exercise challenge, to investigate potential exercise-mediated changes in venous capacitance. The protocol was repeated after alpha-adrenoceptor blockade with prazosin (1 mg kg(-1)M(b)) and again after additional blockade of angiotensin converting enzyme (ACE) with enalapril (1 mg kg(-1)M(b)). In untreated fish, exercise was associated with a rapid (within approx. 1-2 min) and sustained increase in Q and P(ven) associated with a significant increase in MCFP (0.17+/-0.02 kPa at rest to 0.27+/-0.02 kPa at the end of exercise). Prazosin treatment did not block the exercise-mediated increase in MCFP (0.25+/-0.04 kPa to 0.33+/-0.04 kPa at the end of exercise), but delayed the other cardiovascular responses to swimming such that Q and P(ven) did not increase significantly until around 10-13 min of exercise, suggesting that an endogenous humoral control mechanism had been activated. Subsequent enalapril treatment revealed that these delayed responses were in fact due to activation of the RAS, because resting P(da) and R(sys) were decreased further and essentially all cardiovascular changes during exercise were abolished. This study shows that the alpha-adrenergic system normally plays an important role in the control of venous function during exercise in rainbow trout. It is also the first study to suggest that the RAS may be an important modulator of venous pressure and capacitance in fish.
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Affiliation(s)
- Erik Sandblom
- Department of Zoology, Göteborg University, Box 463, S-405 30 Gothenburg, Sweden.
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Sandblom E, Axelsson M. Adrenergic control of venous capacitance during moderate hypoxia in the rainbow trout (Oncorhynchus mykiss): role of neural and circulating catecholamines. Am J Physiol Regul Integr Comp Physiol 2006; 291:R711-8. [PMID: 16741138 DOI: 10.1152/ajpregu.00893.2005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Central venous blood pressure (P(ven)) increases in response to hypoxia in rainbow trout (Oncorhynchus mykiss), but details on the control mechanisms of the venous vasculature during hypoxia have not been studied in fish. Basic cardiovascular variables including P(ven), dorsal aortic blood pressure, cardiac output, and heart rate were monitored in vivo during normoxia and moderate hypoxia (P(W)O(2) = approximately 9 kPa), where P(W)O(2) is water oxygen partial pressure. Venous capacitance curves for normoxia and hypoxia were constructed at 80-100, 90-110, and 100-120% of total blood volume by transiently (8 s) occluding the ventral aorta and measure P(ven) during circulatory arrest to estimate the mean circulatory filling pressure (MCFP). This allowed for estimates of hypoxia-induced changes in unstressed blood volume (USBV) and venous compliance. MCFP increased due to a decreased USBV at all blood volumes during hypoxia. These venous responses were blocked by alpha-adrenoceptor blockade with prazosin (1 mg/kg body mass). MCFP still increased during hypoxia after pretreatment with the adrenergic nerve-blocking agent bretylium (10 mg/kg body mass), but the decrease in USBV only persisted at 80-100% blood volume, whereas vascular capacitance decreased significantly at 90-110% blood volume. In all treatments, hypoxia typically reduced heart rate while cardiac output was maintained through a compensatory increase in stroke volume. Despite the markedly reduced response in venous capacitance after adrenergic blockade, P(ven) always increased in response to hypoxia. This study reveals that venous capacitance in rainbow trout is actively modulated in response to hypoxia by an alpha-adrenergic mechanism with both humoral and neural components.
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Affiliation(s)
- Erik Sandblom
- Dept. of Zoology, Göteborg University, Box 463, S-405 30 Göteborg, Sweden.
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Sandblom E, Farrell AP, Altimiras J, Axelsson M, Claireaux G. Cardiac preload and venous return in swimming sea bass (Dicentrarchus labraxL.). J Exp Biol 2005; 208:1927-35. [PMID: 15879073 DOI: 10.1242/jeb.01606] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYCardiac preload (central venous pressure, Pcv), mean circulatory filling pressure (MCFP), dorsal aortic blood pressure(Pda) and relative cardiac output(Q̇) were measured in sea bass(Dicentrarchus labrax) at rest and while swimming at 1 and 2 BL s-1. MCFP, an index of venous capacitance and the upstream venous pressure driving the return of venous blood to the heart, was measured as the plateau in Pcv during ventral aortic occlusion. Compared with resting values, swimming at 1 and 2 BLs-1 increased Q̇ (by 15±1.5 and 38±6.5%, respectively), Pcv (from 0.11±0.01 kPa to 0.12±0.01 and 0.16±0.02 kPa,respectively), MCFP (from 0.27±0.02 kPa to 0.31±0.02 and 0.40±0.04 kPa, respectively) and the calculated pressure gradient for venous return (ΔPv, from 0.16±0.01 kPa to 0.18±0.02 and 0.24±0.02 kPa, respectively), but not Pda. In spite of an increased preload, the increase in Q̇ was exclusively mediated by an increased heart rate (fh, from 80±4 beats min-1 to 88±4 and 103±3 beats min-1,respectively), and stroke volume (Vs) remained unchanged. Prazosin treatment (1 mg kg-1Mb) abolished pressure and flow changes during swimming at 1 BL s-1, but not 2 BL s-1, indicating that other control systems besides an α-adrenoceptor control are involved. This study is the first to address the control of venous capacitance in swimming fish. It questions the generality that increased Q̇ during swimming is regulated primarily through Vs and shows that an increased cardiac filling pressure does not necessarily lead to an increased Vs in fish, but may instead compensate for a reduced cardiac filling time.
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Affiliation(s)
- Erik Sandblom
- Department of Zoology, Göteborg University, Box 463, S-405 30 Göteborg, Sweden.
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Sandblom E, Axelsson M. Effects of hypoxia on the venous circulation in rainbow trout (Oncorhynchus mykiss). Comp Biochem Physiol A Mol Integr Physiol 2005; 140:233-9. [PMID: 15748864 DOI: 10.1016/j.cbpb.2005.01.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2004] [Revised: 12/17/2004] [Accepted: 01/03/2005] [Indexed: 10/25/2022]
Abstract
Hypoxia in fish is generally associated with bradycardia while cardiac output (Q) remains unaltered or slightly increased due to a compensatory increase in stroke volume (SV). Rainbow trout (Oncorhynchus mykiss) were subjected to severe (P(W)O2=7.3+/-0.2 kPa) or mild (P(W)O2=11.5+/-0.2 kPa) hypoxia. Central venous pressure (P(ven)), dorsal aortic pressure (P(da)), heart rate (f(H)) and Q, were recorded in vivo. Both levels of hypoxia triggered a significant increase in P(ven). Severe hypoxia was associated with bradycardia and unaltered Q, whereas mild hypoxia was associated with a small but significant increase in Q and no bradycardia. These findings indicate that an increase in P(ven) promotes an increase in SV during hypoxia. Since mild hypoxia increased P(ven), Q and SV without bradycardia or reduced systemic resistance (R(sys)), we hypothesize that an active increase in venous tone serving to mobilize blood to the central venous compartment in order to increase cardiac preload and consequently SV, is an important cardiovascular trait associated with hypoxia. Pharmacological pre-treatment with prazosin (1 mg kg(-1)) did not conclusively reveal the underlying mechanisms to the observed changes in P(ven). This study discusses the influence of venous pooling, reduced R(sys) and altered venous tone on changes in P(ven) observed during hypoxia.
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Affiliation(s)
- E Sandblom
- Department of Zoology, Göteborg University, Box 463, S-405 30 Gothenburg, Sweden.
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Sandblom E, Axelsson M. Baroreflex mediated control of heart rate and vascular capacitance in trout. J Exp Biol 2005; 208:821-9. [PMID: 15755880 DOI: 10.1242/jeb.01470] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYThe baroreflex was triggered by altering branchial blood pressure with pre-and post-branchial occlusions for 30 s in rainbow trout Oncorhynchus mykiss. The cardiac limb of the baroreflex was monitored by continuous heart rate (fH) measurements. Responses of venous capacitance vessels were assessed, immediately following either occlusion, by measuring mean circulatory filling pressure (MCFP). Arterial responses were evaluated as the change in dorsal aortic blood pressure(Pda) before and after pre-branchial occlusion. In untreated fish pre-branchial occlusion resulted in tachycardia(62.4±2.4 to 69.1±1.7 beats min–1), decreased venous capacitance reflected as an increase in MCFP (0.17±0.03 to 0.27±0.03 kPa) and increased Pda (4.0±0.2 kPa compared to 3.2±0.1 kPa before occlusion). Post-branchial occlusion somewhat reversed the responses since fH decreased(62.4±2.4 to 53.0±3.1 beats min–1), whereas MCFP remained unaltered. Treatment with the α-adrenergic blocker prazosin (1 mg kg–1) increased resting MCFP to 0.33±0.03 kPa and appeared to abolish both venous and arterial responses to branchial occlusion. Subsequent atropine treatment (1.2 mg kg–1) abolished all chronotropic responses. We present for the first time ample evidence for baroreflex-mediated control of cardiovascular homeostasis, including both the chronotropic and the vascular limb of the baroreflex in an unanaesthetized fish. Furthermore, a novel technique to cannulate and occlude the dorsal aorta, using a Fogarty thru-lumen embolectomy catheter, is explained.
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Affiliation(s)
- E Sandblom
- Department of Zoology, Göteborg University, Box 463, S-405 30 Gothenburg, Sweden.
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Phillips K. TROUT HEARTS DON'T ALWAYS SUCK. J Exp Biol 2004. [DOI: 10.1242/jeb.00800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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