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  • 1
    ISSN: 1420-9071
    Keywords: Cardiac output ; cardio-regulatory nerves ; hemodynamics ; neurohormones ; pericardial organ ; Crustacea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This report provides the first direct measurements of the stroke volume and total cardiac output of crustacean hearts, as recorded from a semi-isolated in vitro preparation. The responses to mechanical perturbations, changes in preload and afterload, show that these hearts do not possess automatic compensatory Frank-Starling-like mechanisms. Heart rate, reflecting the burst rate of the cardiac ganglion, is minimally affected by stretch. On the other hand, these hearts are exquisitely responsive to the neurohormones of the pericardial organs. Serotonin, CCAP and proctolin all produce positive chronotropic and inotropic effects, but the responses to each are unique. Two FMRFamide peptides were positively chronotropic, but negatively inotropic.
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  • 2
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The function of carbonic anhydrase (CA) in the Red Rock Crab,Cancer productus Randall, was investigated. CA activity was found to varying degrees in the gills and many other tissues but not in hemolymph. Crabs injected with acetazolamide, a specific CA inhibitor, demonstrated a significant hemolymph acidosis. Hemolymph CO2 tension ( $$Pa_{CO_2 }$$ ) and CO2 content ( $$Ca_{CO_2 }$$ ) also increased and remained significantly elevated for 96 h following treatment. No significant changes could be detected in either hemolymph oxygenation or ionic status (except for HCO 3 − ) as a result of acetazolamide treatment. Crabs treated with acetazolamide, and also exposed to air, exhibited a more pronounced hemolymph acidosis with significantly increased respiratory ( $$P_{CO_2 }$$ ) and metabolic (lactate) components compared with the control group. Upon reimmersion acetazolamide treated crabs showed a slower recovery of hemolymph pH compared with the control group and no significant removal of the total CO2 load induced by air exposure. No significant differences between experimental and control groups during air exposure and recovery could be detected in hemolymph oxygenation, ionic status, NH3+NH 4 + levels or respiratory and cardiac pumping frequency and so the effects of acetazolamide treatment were apparently limited to CO2 removal across the gills. These results indicate that branchial CA facilitates the removal of CO2 from the hemolymph of SW adaptedC. productus largely by catalyzing the dehydration of hemolymph HCO 3 − to molecular CO2 at the gill. It is also recognized that gill CA may also serve to hydrate molecular CO2 to H+ and HCO3/− for use as counterions for ionic uptake mechanisms. Crab gill CA thus appears to play an important role in CO2 excretion as well as hemolymph ionic regulation.
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  • 3
    ISSN: 1432-136X
    Keywords: Key words Cardiovascular ; Hypoxia ; Crustacea ; Respiratory ; Doppler
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The heart rate of crayfish (Procambarus clarkii) and lobsters (Homarus americanus) decreased (bradycardia) as partial pressure of O2 (P O 2) decreased, yet cardiac output (V b) was maintained via an increased stroke volume (S v) to P O 2s of 40 mmHg and 75 mmHg for crayfish and lobsters, respectively. V b was redistributed in both animals. Flow through the anterior aorta increased while flow dropped through the posterior aorta and sternal artery to a P O 2 of 30 mmHg; below this flow was no longer maintained in crayfish. In the lobster, flow increased to the lateral arteries and the ventral thoracic artery while flow through the anterior and posterior aortas, sternal artery and ventral abdominal artery decreased to a P O 2 of 75 mmHg. Anterior hemolymph flow was maintained or increased in both animals presumably to supply nervous tissue and cephalic sense organs better. Crayfish showed an increase in intracardiac and mean arterial hemolymph pressures as P O 2 declined. The increased pressures combined with the net increase in cardiac filling pressure and diastolic filling time could have accounted for the increased S V. The cardiovascular response exhibited by both the crayfish and lobster was P O 2 dependent; below a critical water P O 2 active compensation was no longer observed.
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  • 4
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary At the onset of moderate swimming activity,Callinectes sapidus rapidly increased branchial ventilation, heart rate, and oxygen uptake, reaching steady state values in 2–3 min, with a half-time of 30 sec. Although O2 extraction efficiency decreased slightly (50% to 43%) upon reaching steady state, O2 uptake was increased 2.6 fold over resting (routine) levels. HemolymphP O 2 did not change during sustained (30–60 min) exercise, but a marked decrease in pH (7.60 to 7.10), associated with a 14-fold increase in hemolymph lactate concentration, caused decreases in both pre-and postbranchial O2 content due to a large hemocyanin Bohr shift. The effect of the Bohr shift on O2 binding, however, was minimized by an increase in hemocyanin O2 affinity induced by lactate ions; the influence of lactate on hemocyaninP 50 was shown to be the same in vivo and in vitro. As a result of the interaction between the Bohr and lactate effects, only slight increases were observed in the a-v O2 difference (13%) and the quantitative role of hemocyanin in oxygen transport (11%) during exercise. The increase in O2 delivery was therefore attributed primarily to a 2.3 fold increase in cardiac output (Fick estimate), resulting from increases in both heart rate (1.61 X) and stroke volume (1.42X). During exercise hemocyanin remained 21% oxygenated upon leaving the tissues, thus maintaining a substantial ‘venous O2 reserve’ which could be utilized to fuel more strenuous levels of exercise at least partly by aerobic pathways. The high hemolymph lactate levels, however, indicate that anaerobic metabolism makes a significant contribution to energy production even during moderate exercise. These results are similar to the respiratory and circulatory responses reported for other decapod crustaceans and fish during mild exercise.C. sapidus, however, appears to be highly resistant to fatigue, which correlates with its welldeveloped locomotor capabilities.
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  • 5
    ISSN: 1432-136X
    Keywords: Proctolin ; Crustacean cardioactive peptide ; Cardiovascular ; Circulation ; Crab, Cancer magister
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Decapod crustacean pericardial organs contain extensive neurohormonal reserves which can be released directly into the haemolymph to act as physiological modulators. The present paper concerns the in vivo effects of two pericardial peptides, proctolin and crustacean cardioactive peptide, on cardiovascular dynamics in the crab Cancer magister. Infusion of proctolin into the pericardial sinus caused a slight decrease in heart rate concurrent with a large increase in cardiac stroke volume. It decreased haemolymph flow anteriorly through the paired anterolateral arteries and increased flow posteriorly and ventrally through the posterior aorta and sternal artery, respectively. The threshold for responses occurred at circulating concentrations of 10-9 mol·l-1, and haemolymph flows remained elevated for up to 30 min after peptide infusion. The effects of crustacean cardioactive peptide were less dramatic. Heart rate was not affected but a significant increase in stroke volume was observed. Crustacean cardioactive peptide increased haemolymph flow through the anterolateral arteries and increased scaphognathite rate. The threshold for crustacean cardioactive peptide activity was higher than for proctolin (10-7 mol·l-1 and 10-6 mol·l-1) but the responses to crustacean cardioactive peptide were of longer duration. The effects of proctolin on regional haemeolymph distribution in Cancer magister closely resemble the cardiovascular responses of this species when exposed to hypoxic conditions. These peptides may be implicated as cardiovascular regulators during environmental perturbations.
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  • 6
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Command fibers located in the circumesophageal connectives which modify scaphognathite and heart rhythms have been mapped and characterized in the crab,Cancer magister. Behavior: Crabs show a variety of responses to external stimuli often including simultaneous cessation of cardiac and scaphognathite “pumping”. Habituation and a return to prestimulus rhythms results from continued stimulation. The response to short stimulus durations, on the other hand, generally outlasts the stimulus indicating the playing-out of a motor program. Neurophysiology: Small bundles of fibers have been isolated from desheathed connectives. Activity in these fibers resulting from stimulation of various anterior sensory receptors was recordeden passant with suction electrodes. When sensory stimulation produced both electrical activity in the nerves under examination and a cardiac and/or scaphognathite response it was assumed such units were involved in inducing this response. This was tested by electrical stimulation delivered through the same electrode. Those units which produced similar responses to natural and artificial stimulation were deemed “command fibers”. It was invariably found that the minimum stimulating frequency needed to mimic naturally induced responses was much greater than the frequency at which the units discharged in response to those stimuli. During mapping experiments, command fibers were characterized with respect to their positions in the connectives and by the responses they produced at different frequencies of stimulation. 68% of the fibers identified affected both cardiac and scaphognathite systems, 29% the scaphognathites alone and 3% the heart alone. The frequency-response profiles of single bivalent command fibers were often different from the heart and scaphognathites. These findings help explain the responses of both systems to natural stimuli and also indicate that the circulatory and respiratory systems not only perform in concert, but are often under common control.
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  • 7
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Adult male Dungeness crab, Cancer magister, were trapped in the Barkley Sound region of Vancouver Island, British Columbia during June 1992 to August 1993. Heart rate and haemolymph flow through the five major arterial systems were recorded in resting undisturbed C. magister using a pulsed Doppler flowmeter. This technique allowed calculation of the stroke volume of the heart as well as cardiac output. The heart rate of 62 C. magister conformed to a normal distribution, whereas haemolymph flow through individual arteries was exponentially distributed. Stable haemolymph flow through all arterial systems was observed in only about 5% of the individuals tested; more often, haemolymph flow in one or more arteries fluctuated independently of flow through the remaining arteries. Several typical patterns of variation in cardiovascular parameters are described and related to possible underlying control mechanisms.
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  • 8
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Oxygen transport by the hemocyanin of the protobranch mollusc Solemya reidi Bernard was studied in native hemolymph samples. Clams were collected from two different reducing environments, beneath log booms in Alberni Inlet, British Columbia, Canada, and from the sewage effulent in Santa Monica Bay, California, USA. The hemocyanin concentration in a pooled hemolymph sample (n = 10 individuals) was 33.5 mg ml−1. The mean hemolymph pH of five Alberni clams maintained for 3 wk in mud was 7.96 ± 0.06. No significant variation in hemocyanin oxygen-affinity or cooperativity was found for hemocyanin in whole hemolymph samples from these five individually studied clams. There was a significant difference only at 15 °C in the oxygen affinity of hemocyanin in pooled whole-hemolymph samples from S. reidi collected from Alberni Inlet compared with clams collected from Santa Monica Bay. Little effect of temperature on hemocyanin oxygen-affinity was found for temperatures below 20 °C; above 20 °C, the oxygen affinity was reduced for clams from both sites. Temperature and pH had no apparent affect on hemocyanin cooperativity. Moderate Bohr shifts were found at all temperatures examined. The presence of physiologically relevant concentrations of thiosulphate in hemocyanin samples resulted in a decrease in hemocyanin oxygen-affinity, opposite to the effect on hemocyanin found for the hydrothermal vent crab Byth-ograea thermydron, but thiosulphate had no effect on hemocyanin cooperativity.
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