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Optimizing oxygen delivery to the fish heart
Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S115–S123
currently support, this would help us understand how the Root effect was selected for prior to the evolution of the beta-NHE, choroid gland and retia of the eye, and the SB gas gland and rete mirabile. doi:10.1016/j.cbpa.2008.04.261
A6.7 Optimising peripheral oxygen transport by means of microvascular remodelling S. Egginton (University of Birmingham) Angiogenesis may result from a mismatch in microvascular supply and metabolic demand, or in response to an altered haemodynamic environment. The heterogeneity in response within a muscle may therefore reflect either differences in fibre type composition or mechanical load. Control is exerted at a local level as seen by the specificity in location of angiogenesis to glycolytic fibre types following muscle stimulation (Badr et al., 2003), while heterogeneity of capillary spacing is maintained during ontogenetic growth (Degens et al., 2006). In order to avoid bias due to scaling effects (capillarity is highly dependent on fibre size) it is necessary to move from a number- to an area-based analysis of capillary supply. This allows a capillary-by-capillary and a fibre-by-fibre analysis of the angiogenic response to physiological challenges such as training, ischaemia, and myopathic atrophy. In doing so, it generates a space-filling alternative to Krogh's cylinder model of tissue oxygenation termed the capillary domain (Egginton and Ross, 1992). This allows the influence of changes in extent and location of angiogenesis to be explored. A refinement being developed incorporates algorithms describing intracellular diffusion to explore the consequences for muscle fibre oxygen tension, and the extent to which various elements of the oxygen transport cascade are optimised. References Badr, et al., 2003. Exp Physiol 88, 565–568. Degens, et al., 2006. Microcirculation 13.6, 467–476. Egginton, Ross (Eds.), 1992. Oxygen Transport in Biological Systems: Modelling of Pathways from Environment to Cell. CUP. doi:10.1016/j.cbpa.2008.04.262
A6.8 Effects of feeding and temperature on gastrointestinal blood flow in the Antarctic fish Pagothenia borchgrevinki; different or just another teleost? M. Axelsson (Göteborg University) Abstract not available
The first vertebrate hearts had a spongy myocardium that utilised whatever oxygen remained in venous blood following extraction by systemic tissues. A coronary circulation and air breathing both have evolved numerous times in fishes and supplement the heart's venous oxygen supply. However, the spongy myocardium has never been completely replaced by compact myocardium. Also, highly developed coronary circulation can be found in an air breathing fish, challenging the notion that air breathing evolved in fishes to provide a more secure myocardial oxygen supply during exercise. The oxygen supply of the spongy myocardium is indeed challenged by exhaustive exercise, as well as by increased temperature and environmental hypoxia, largely because venous oxygen content decreases. Nevertheless, the potential importance of the temperaturedependence and the pH-dependence of the Hb–oxygen dissociation curve in optimizing cardiac oxygen supply under such conditions are examined here. Research support provided by NSERC Canada. doi:10.1016/j.cbpa.2008.04.264
A6.10 Does autonomic regulation of heart rate optimise oxygen uptake in teleost fishes? D. McKenzie (CNRS Montpellier); E. Taylor (Birmingham); T. Wang (Aarhus); P. Skov (MBL Helsingoer); J. Steffensen (MBL Helsingoer); H. Campbell (Queensland); C. Leite (UNESP Rio Claro); A. Abe (UNESP Rio Claro) Autonomic regulation of heart rate in teleosts has been proposed to optimise oxygen uptake by matching perfusion to ventilation of respiratory organs. A series of studies were performed, combining manipulation of cardiac control with instantaneous respirometry, to investigate two responses where autonomic control may have this role. In hypoxia, water-breathing fishes show a bradycardia which has been proposed to optimise patterns of gill perfusion. This is an O2chemoreflex mediated by the cardiac vagus, section of this nerve abolished the chemoreflex in Atlantic cod (Gadus morhua). However, denervated and sham-operated cod showed the same ability to regulate oxygen uptake during progressive hypoxia. In deep hypoxia, though, denervates exhibited cardiac failure that was never observed in shams. In teleosts with bimodal respiration, surface air-breathing is associated with exhalation bradycardia followed by inhalation tachycardia, which have been proposed to optimise oxygen uptake from the air-breathing organ. These frequency variations are almost exclusively due to modulation of inhibitory cholinergic tone in two neotropical species, the jeju (Hoplerythrinus unitaeniatus) and the swamp eel (Synbranchus marmoratus). The jeju surfaced for single air-breaths, associated with precise beatto-beat modulation of heart rate, with cholinergic and adrenergic tones varying in synchrony, not antagonistically. Synbranchus remained at the surface to breathe in bouts, associated with very large increases in heart rate and cardiac output; an element of these responses was not under autonomic control. Pharmacological blockade of autonomic regulation did not, however, change the efficacy by which either species maintained their routine metabolic rate by air-breathing in deep hypoxia.
doi:10.1016/j.cbpa.2008.04.263 doi:10.1016/j.cbpa.2008.04.265
A6.9 Optimizing oxygen delivery to the fish heart A. Farrell, M. Steinhausen, T. Clark, L. Hanson (University of British Columbia)
S117
A6.11 Control of cardiorespiratory interactions in fish E. Taylor (Birmingham University)
currently support, this would help us understand how the Root effect was selected for prior to the evolution of the beta-NHE, choroid gland and retia of the eye, and the SB gas gland and rete mirabile. doi:10.1016/j.cbpa.2008.04.261
A6.7 Optimising peripheral oxygen transport by means of microvascular remodelling S. Egginton (University of Birmingham) Angiogenesis may result from a mismatch in microvascular supply and metabolic demand, or in response to an altered haemodynamic environment. The heterogeneity in response within a muscle may therefore reflect either differences in fibre type composition or mechanical load. Control is exerted at a local level as seen by the specificity in location of angiogenesis to glycolytic fibre types following muscle stimulation (Badr et al., 2003), while heterogeneity of capillary spacing is maintained during ontogenetic growth (Degens et al., 2006). In order to avoid bias due to scaling effects (capillarity is highly dependent on fibre size) it is necessary to move from a number- to an area-based analysis of capillary supply. This allows a capillary-by-capillary and a fibre-by-fibre analysis of the angiogenic response to physiological challenges such as training, ischaemia, and myopathic atrophy. In doing so, it generates a space-filling alternative to Krogh's cylinder model of tissue oxygenation termed the capillary domain (Egginton and Ross, 1992). This allows the influence of changes in extent and location of angiogenesis to be explored. A refinement being developed incorporates algorithms describing intracellular diffusion to explore the consequences for muscle fibre oxygen tension, and the extent to which various elements of the oxygen transport cascade are optimised. References Badr, et al., 2003. Exp Physiol 88, 565–568. Degens, et al., 2006. Microcirculation 13.6, 467–476. Egginton, Ross (Eds.), 1992. Oxygen Transport in Biological Systems: Modelling of Pathways from Environment to Cell. CUP. doi:10.1016/j.cbpa.2008.04.262
A6.8 Effects of feeding and temperature on gastrointestinal blood flow in the Antarctic fish Pagothenia borchgrevinki; different or just another teleost? M. Axelsson (Göteborg University) Abstract not available
The first vertebrate hearts had a spongy myocardium that utilised whatever oxygen remained in venous blood following extraction by systemic tissues. A coronary circulation and air breathing both have evolved numerous times in fishes and supplement the heart's venous oxygen supply. However, the spongy myocardium has never been completely replaced by compact myocardium. Also, highly developed coronary circulation can be found in an air breathing fish, challenging the notion that air breathing evolved in fishes to provide a more secure myocardial oxygen supply during exercise. The oxygen supply of the spongy myocardium is indeed challenged by exhaustive exercise, as well as by increased temperature and environmental hypoxia, largely because venous oxygen content decreases. Nevertheless, the potential importance of the temperaturedependence and the pH-dependence of the Hb–oxygen dissociation curve in optimizing cardiac oxygen supply under such conditions are examined here. Research support provided by NSERC Canada. doi:10.1016/j.cbpa.2008.04.264
A6.10 Does autonomic regulation of heart rate optimise oxygen uptake in teleost fishes? D. McKenzie (CNRS Montpellier); E. Taylor (Birmingham); T. Wang (Aarhus); P. Skov (MBL Helsingoer); J. Steffensen (MBL Helsingoer); H. Campbell (Queensland); C. Leite (UNESP Rio Claro); A. Abe (UNESP Rio Claro) Autonomic regulation of heart rate in teleosts has been proposed to optimise oxygen uptake by matching perfusion to ventilation of respiratory organs. A series of studies were performed, combining manipulation of cardiac control with instantaneous respirometry, to investigate two responses where autonomic control may have this role. In hypoxia, water-breathing fishes show a bradycardia which has been proposed to optimise patterns of gill perfusion. This is an O2chemoreflex mediated by the cardiac vagus, section of this nerve abolished the chemoreflex in Atlantic cod (Gadus morhua). However, denervated and sham-operated cod showed the same ability to regulate oxygen uptake during progressive hypoxia. In deep hypoxia, though, denervates exhibited cardiac failure that was never observed in shams. In teleosts with bimodal respiration, surface air-breathing is associated with exhalation bradycardia followed by inhalation tachycardia, which have been proposed to optimise oxygen uptake from the air-breathing organ. These frequency variations are almost exclusively due to modulation of inhibitory cholinergic tone in two neotropical species, the jeju (Hoplerythrinus unitaeniatus) and the swamp eel (Synbranchus marmoratus). The jeju surfaced for single air-breaths, associated with precise beatto-beat modulation of heart rate, with cholinergic and adrenergic tones varying in synchrony, not antagonistically. Synbranchus remained at the surface to breathe in bouts, associated with very large increases in heart rate and cardiac output; an element of these responses was not under autonomic control. Pharmacological blockade of autonomic regulation did not, however, change the efficacy by which either species maintained their routine metabolic rate by air-breathing in deep hypoxia.
doi:10.1016/j.cbpa.2008.04.263 doi:10.1016/j.cbpa.2008.04.265
A6.9 Optimizing oxygen delivery to the fish heart A. Farrell, M. Steinhausen, T. Clark, L. Hanson (University of British Columbia)
S117
A6.11 Control of cardiorespiratory interactions in fish E. Taylor (Birmingham University)