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Structure and Function of the Fish Cardiac Ventricle - Flexibility and Limitations
No full textFishes show the highest diversity among vertebrates. Defined differences in ventricular myoarchitecture exist in fish. There are two main types of cardiac ventricle in fish: a spongy type and a mixed type. In the spongy ventricle, the muscle trabeculae form a sponge-like network the spongiosa. In the mixed ventricle, one or more superficial layers of compact tissue (compacta) enclose an inner spongiosa. The spongiosa and compacta are respectively associated with a lacunary and a vascularized supply of blood. Interspecies differences exist in the proportion of compacta and the extent of vascularization. Here the mechanical limits and flexibility of the different types of ventricular organization are examined. The spongy type (found only in teleosts) seems to be particularly suitable for pel forming volume work. An example is the icefish heart. The main characteristics of this fish are the absence of hemoglobin in the blood and the very large volume of blood. The cardiac ventricle of the icefish is characterized by a cardiomegaly of the spongy type with myocardial pseudohypertrophy It functions as a specialized volume pump which moves large stroke volumes at a low heart rate, but is not able to produce high pressures. The most active teleosts have mixed heart ventricles with different thicknesses of compacta. The presence of compacta gives these types of heart the potential to act as pressure pumps: they move small volumes at a relatively high rate and high pressure. The tuna heart is an extreme example of the mixed type. It has the highest relative mass and proportion of compacta (40-70%) among fishes. Tt can beat at a high rate and produce up to 18 kPa of pressure. The performance of this heart seems to be highly dependent on the adequate perfusion of the coronaries. Insights into the significance of coronary perfusion in terms of ventricular mechanical behavior can be given by the comparison between hearts in which the vascularization is limited to the compacta (such as the trout heart) and hearts in which the vascularization extends to the spongiosa (like the elasmobranch heart)
Myocardial and Coronary Effects of Exogenous Arachidonic-acid On the Isolated and Perfused Heart Preparation and Its Metabolism In the Heart of Trout (oncorhynchus-mykiss)
No full text1. The effects of arachidonate (AA) on myocardial and coronary function, and the ability to metabolize AA have been explored for the first time in the heart of rainbow trout, Oncorhynchus mykiss. 2. On the isolated and perfused working heart exogenous AA (10(-7) and 10(-5) M) elicits a significant reduction of cardiac output and power output while heart rate is unaffected. 3. The negative inotropic effect is abolished in presence of 10(-5) M indomethacin. At the same AA concentration a pronounced increase in coronary resistance (175% change from baseline values) is apparent which is reduced but not abolished in the presence of 10(-5) M indomethacin. 4. C-14-arachidonate is metabolized by trout ventricle homogenate into PGs E2, F2alpha, D2, and in lesser amount into TXB2 and 6-keto-PGF1alpha. Ca-ionophore A23187 enhances the production of both PGE2 and PGF2alpha. The lipoxygenase products assayed as the hydroxy acids (HETEs) appear to be less actively synthesized than prostanoids
Mechanical Performance of the Isolated and Perfused Heart of the Haemoglobinless Antarctic Icefish Chionodraco hamatus (Lonnberg): Effects of Loading Conditions and Temperature
No full textScaling of heart ventricle mass and body mass in the haemoglobinless Antarctic fish Chionodraco hamatus Lonnberg shows a relationship similar to those reported for other 'cardiomegalic' icefish (Chaenocephalus aceratus and Channichthys rhinoceratus). An in vitro preparation of the heart of C. hamatus was set up to investigate the mechanical performance of this heart at different preloads and afterloads. It appears that this heart is well adapted to working within a range of preloads varying from -0.07 to -0.04 kPa, while it is unable to sustain increases of afterloads higher than 3.0 kPa. As in other teleosts, heart rate is unaffected by changes in preload and afterload. Increase in temperature from 0.5 to 5.8-degrees-C affects heart rate whereas stroke volume is unaffected. On the whole, the in vitro data are similar to those in vivo measured in another icefish, C. aceratus and show that the heart of C. hamatus works as a typical volume pump. This is discussed in relation to both the structural constraints related to the cardiac design of this icefish and the biology of this unique vertebrate
Coronary Drainage In the Octopus-vulgaris Systemic Heart
No full textThe vascular architecture of the coronary system of the systemic heart of the octopus (Octopus vulgaris) has been studied by means of both the corrosion-cast method and scanning electron microscopy. It is shown that the Octopus systemic heart myocardium is supplied through a very rich capillary network, the complexity of which probably reflects the complex organization of the ventricular wall. Drainage occurs by way of a classic venous system that originates from this capillary network. Morphological evidences are reported indicating that the coronary bed communicates directly with the ventricular lumen. In the isolated perfused systemic heart, the flow through this system is related directly to cardiac contractility. In an in situ preparation of the systemic heart, where for the first time simultaneous records have been obtained, ventricular pressure, coronary vein pressure, and coronary flow appear to be time related. It is suggested that in Octopus the venous coronary flow is not dependent on the systemic arterial pressure, as in the vertebrate heart, but it is directly dependent on intraventricular pressure
In vitro cardiac performance in the sub-antarctic notothenioids Eleginops maclovinus (subfamily eleginopinae), Paranotothenia magellanica, and Patagonotothen tessellata (subfamily nototheniinae)
No full textThere is lack of information concerning species diversification in the Non-Antarctic Nototheniid fish both in relation with their variation in organismal performance and in the morphofunctional characteristics underlying this variation. This work was designed to study in three Sub-Antarctic Nototheniids, Eleginops maclovinus, Patagonotothen tessellata, and Paranotothenia magellanica, cardiocirculatory features that may reflect interspecific differences in organismal performance, which in rum may explain aspects of evolutionary and ecological diversity. Haematocrit values were similar in all three species (between 28 and 3?), being in the range of that observed in other red-blooded Notothenioids. In all species, the heart ventricle was fully trabeculated (Type I ventricle) with P. tessellata and P. magellanica having higher relative ventricle weights than E. maclovinus. The latter species was characterized by unique spindle-shaped ventricle, apparently caused by the insertion of a pair of respiratory muscles on either side of the pericardial cavity. Intrinsic cardiac performance was assessed using an in vitro isolated and perfused heart preparation working under loading conditions. Common trends in the three species were a) the intrinsic heart rate higher than that shown by the Antarctic counterparts, b) stroke volume positively related to preload and inversely to afterload, c) pressure work exhibiting higher cost (in terms of oxygen consumption) than volume work, and d) higher mechanical efficiency under volume loading than under pressure loading. There were clearly defined interspecific differences in cardiac mechanical performance between the two Nototheniinae and E. maclovinus. The heart of the latter differed from those of the Nototheniinae, particularly in its incapacity to maintain constant stroke volume and cardiac output under pressure loading. This finding may be relevant for evaluating organismal performance in light of Notothenioid diversification. (C) 1997 Elsevier Science Inc
Chronotropic and Inotropic Effects of Atrial Peptides On the Isolated Systemic Heart of Octopus-vulgaris
No full textThe chronotropic and inotropic effects of four atrial peptides (cardiodilatin 1-16, atrial natriuretic factor 8-33 and atriopeptin I and III) on the isolated systemic heart of Octopus vulgaris were studied. Using a preparation that produces a physiological stroke volume at physiological input pressures, it was found that ANF, atriopeptin I and atriopeptin III exerted both negative chronotropic and inotropic effects. In contrast, cardiodilatin produced a positive inotropic effect. A dose-response curve of ANF is reported, showing a threshold concentration of about 10(-12) M. The pharmacological and physiological implications of these results are discussed in relation to some characteristics of the cephalopod systemic heart
Nitric oxide modulates cardiac performance in the heart of Anguilla anguilla.
No full textNothing is known about the effects of nitric oxide (NO) on cardiac performance in fish. Using an in vitro working heart preparation that generates physiological values of output pressure, cardiac output and ventricular work and power, we assessed the effects of NO on the cardiac performance of the eel Anguilla anguilla. We examined basal cardiac performance (at constant preload, afterload and heart rate), the effects of cholinergic stimulation and the Frank-Starling response (preload-induced increases in cardiac output at constant afterload and heart rate). The NO synthase (NOS) inhibitors NG-monomethyl-L-arginine (L-NMMA) and L-N5(1-iminoethyl)ornithine (L-NIO), the guanylate cyclase inhibitor 1H-(1,2,4)oxadiazolo-(4,3-a)quinoxalin-1-one (ODQ) and Triton X-100, a detergent that damages the endocardial endothelium, all increased stroke volume (VS) and stroke work (WS). In contrast, the endogenous NOS substrate L-arginine, tested before and after treatment with haemoglobin, the NO donor 3-morpholinosydnonimine, tested with and without the superoxide scavenger superoxide dismutase, and the stable cGMP analogue 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) decreased VS and WS. Acetylcholine chloride produced a biphasic effect. At nanomolar concentrations, in 34 \% of the preparations, it induced a NO-cGMP-dependent positive inotropism that required the integrity of the endocardial endothelium. Pretreatment with Triton X-100 or with NO-cGMP pathway inhibitors (L-NMMA, L-NIO, NG-nitro-l-arginine methyl ester, Methylene Blue and ODQ) abolished the positive effect of acetylcholine. In contrast, at micromolar concentrations, acetylcholine produced a negative effect that involved neither the endocardial endothelium nor the NO-cGMP pathway. Pre-treatment with L-arginine (10(-6 )mol x l(-1)) was without effect, whereas L-NIO (10(-5 )mol x l(-1)) significantly reduced the Frank-Starling response. Taken together, these three experimental approaches provide evidence that NO modulates cardiac performance in the eel heart
Effects of Cardiodilatin 1-16 and Anf On the Coronary Flow In the Isolated Systemic Heart of Octopus-vulgaris
No full text1. The effects of cardiodilatin1–16 and atrial natriuretic factor (ANF) on the coronaryflow in the Octopusvulgaris were studied in vitro by using a preparation of the isolated and perfused systemicheart that produces physiological stroke volumes at physiological load conditions.
2. Both cardiodilatin1–16 and ANF have negative inotropic effects on the isolatedsystemicheart, and cause a significant increase of the coronary stroke volume.
3. The increase of coronary stroke volume is mainly the consequence of the reduction of coronary resistance in the presence of these peptides
The Systemic Heart of Octopus-vulgaris - Effects of Exogenous Arachidonic-acid and Capability For Arachidonate Metabolism
No full textThe actions of exogenous arachidonic acid on the performance of the isolated and perfused systemic heart of Octopus vulgaris (collected in the Bay of Naples in 1992), and the potential of this heart for eicosanoid synthesis are described. Arachidonic acid induces positive chronotropic and inotropic effects. The positive inotropic effect is apparent only at the lowest concentration used (10(-7) M) and in the paced heart preparations, in which a negative relationship between stroke volume and heart rate has been demonstrated. Using 10(-5) M arachidonate, which induces the greatest chronotropic effect, a reduction of inotropism is evident which is due to the above negative relationship between stroke volume and heart rate. These effects are scarcely affected by the cyclooxygenase and lipoxygenase inhibitors, indomethacin (IM) and nordihydroguaiaretic acid (NDGA), respectively. On the coronary system of this heart arachidonic acid displays a potent vasoconstrictory action (ca. 100 percent increase of coronary resistance). This effect is potentiated by IM and reduced by NDGA. C-14-arachidonate is metabolized by the octopus ventricle homogenate into the lipoxygenase products (assayed as hydroxy acids) more actively than into cyclo-oxygenase products (prostanoids: PGE(2), PGD(2), PGF(2 alpha), and 6-keto-PGF(1 alpha)). On the other hand, the Ca ionophore A23187 enhances the production of cyclooxygenase metabolites much more than of lipoxygenase metabolites
Performance of the Isolated and Perfused Working Heart of the Teleost Conger-conger - Study of the Inotropic Effect of Prostacyclin
No full textAn in vitro preparation of the heart of the teleostConger conger, isolated without the pericardium, was set up. The procedure allowed subambient pressures to develop in the perfusion chamber during contraction, mimicking the in vivo situation with the pericardium intact. The ventricle produced a cardiac output of about 15 ml·min-1·kg wet body weight-1 at subambient input pressure, and was able to double the stroke work with an increase of preload up to about 0.2 kPa. Using this preparation it was found that prostacyclin has a positive inotropic effect on the atrium and ventricle, but it does not affect the heart rate. Semilogarithmic doseresponse curves of prostacyclin on the atrium are reported, showing a threshold concentration of about 10-9 M. The isolated and perfusedConger conger heart provides a useful model for a detailed analysis of the action of prostacyclin on myocardial contractility
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