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  • 1. Forster, M E
    et al.
    Davison, W
    Axelsson, M
    Sundin, L
    Franklin, C E
    Gieseg, S
    Catecholamine release in heat-stressed Antarctic fish causes proton extrusion by the red cells1998In: Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, ISSN 0174-1578, E-ISSN 1432-136X, Vol. 168, no 5, p. 345-352Article in journal (Refereed)
    Abstract [en]

    Two species of Antarctic fish were stressed by moving them from seawater at -1 degrees C to seawater at 10 degrees C and holding them for a period of 10 min. The active cryopelagic species Pagothenia borchgrevinki maintained heart rate while in the benthic species Trematomus bernacchii there was an increase in heart rate. Blood pressure did not change in either species. Both species released catecholamines into the circulation as a consequence of the stress. P. borchgrevinki released the greater amounts, having mean plasma concentrations of 177 +/- 54 nmol.l(-1) noradrenaline and 263 +/- 131 nmol.l(-1) adrenaline at 10 min. Pla.sma noradrenaline concentrations rose to 47 +/- 14 nmol.l(-1) and adrenaline to 73 +/- 28 nmol.l(-1) in T. bernacchii. Blood from P. borchgrevinki was tonometered in the presence of isoprenaline. A fall in extracellular pH suggests the presence of a Na+/H+ antiporter on the red cell membrane, the first demonstration of this in an Antarctic fish. Treatment with the beta-adrenergic antagonist drug sotalol inhibited swelling of red blood cells taken from temperature-stressed P. borchgrevinki, suggesting that the antiporter responds to endogenous catecholamines.

  • 2. Sandblom, Erik
    et al.
    Axelsson, Michael
    Davison, William
    Circulatory function at sub-zero temperature: venous responses to catecholamines and angiotensin II in the Antarctic fish Pagothenia borchgrevinki2009In: Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, ISSN 0174-1578, E-ISSN 1432-136X, Vol. 179, no 2, p. 165-173Article in journal (Refereed)
    Abstract [en]

    Catecholamines increase arterial pressure by increasing cardiac output (Q) and stroke volume (V (s)), while angiotensin II (ang II) also increases vascular resistance (R (sys)) in the Antarctic fish Pagothenia borchgrevinki. Adrenaline, phenylephrine and ang II (Asn(1), Val(5)) were injected into P. borchgrevinki. Cardiovascular variables, including central venous pressure (P (cv)) and mean circulatory filling pressure (P (mcf); an index of venous capacitance), were recorded to investigate if venous vasoconstriction can explain the increased V (s) and Q and the arterial pressor response in this species. Routine P (cv) and P (mcf) were 0.11 +/- A 0.01 and 0.18 +/- A 0.02 kPa, respectively. All of the drugs caused moderate increases in P (cv) and P (mcf) and the responses were attenuated after alpha-adrenergic blockade with prazosin. Although dorsal aortic pressure (P (da)) also increased in response to all agonists, the mechanisms differed. Adrenaline caused sustained increases in V (s) and Q, while R (sys) only rose transiently. Ang II had a slower effect than adrenaline and increased both R (sys) and Q, while phenylephrine only increased R (sys). This study demonstrates that P (cv) is positive and controlled by an alpha-adrenergic mechanism in P. borchgrevinki. However, given the relatively small venous response to adrenaline it seems more likely that the increases in V (s) and Q from this agonist are due to direct effects on the heart.

  • 3. Sandblom, Erik
    et al.
    Axelsson, Michael
    Davison, William
    Enforced exercise, but not acute temperature elevation, decreases venous capacitance in the stenothermal Antarctic fish Pagothenia borchgrevinki2008In: Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, ISSN 0174-1578, E-ISSN 1432-136X, Vol. 178, no 7, p. 845-851Article in journal (Refereed)
    Abstract [en]

    The venous haemodynamic response to enforced exercise and acute temperature increase was examined in the Antarctic fish Pagothenia borchgrevinki (borch) to enable comparisons with the existing literature for temperate species, and investigate if the unusual cardiovascular response to temperature changes previously observed in the borch can be linked to an inability to regulate the venous vasculature. Routine central venous blood pressure (P(cv)) was 0.08 kPa and the mean circulatory filling pressure (P(mcf); an index of venous capacitance) was 0.14 kPa. Acute warming from 0 to 2.5 and 5 degrees C increased heart rate (f(H)), while dorsal aortic blood pressure (P(da)) decreased. P(mcf) did not change, while P(cv) decreased significantly at 5 degrees C. This contrasts with the venoconstriction previously observed in rainbow trout in response to increased temperature. Exercise resulted in small increases in P(mcf) and P(cv), a response that was abolished by alpha-adrenoceptor blockade. This study demonstrates that the heart of P. borchgrevinki normally operates at positive filling pressures (i.e. P(cv)) and that venous capacitance can be actively regulated by an alpha-adrenergic mechanism. The lack of decrease in venous capacitance during warming may suggest that a small increase in venous tone is offset by a passive temperature-mediated increase in compliance.

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