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First published online October 5, 2006
Journal of Experimental Biology 209, 4167-4173 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02459

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Cardiovascular changes under normoxic and hypoxic conditions in the air-breathing teleost Synbranchus marmoratus: importance of the venous system

Marianne Skals^1,2,*, Nini Skovgaard^1,2, Edwin W. Taylor^2,3, Cleo A. C. Leite^2,4, Augusto S. Abe² and Tobias Wang^1,2

¹ Zoophysiology, Department of Biological Sciences, University of Aarhus, 8000 Aarhus, Denmark
² Departamento de Zoologia, Centro de Aquicultura, UNESP, Rio Claro, São Paulo, Brazil
³ School of Biosciences, The University of Birmingham, UK
⁴ Department of Physiological Sciences, Federal University of São Carlos, São Paulo, Brazil

^* Author for correspondence (e-mail: marianne.skals{at}biology.au.dk)

Accepted 25 July 2006

Synbranchus 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 (V_S), 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 (), heart rate (f_H), central venous blood pressure (P_CV), mean circulatory filling pressure (MCFP), and dorsal aortic blood pressures (P_DA) in S. marmoratus. Measurements were performed in aerated water (P_O2>130 mmHg), when the fish alternated between gill ventilation and prolonged periods of apnoeas, as well as during hypoxia (P_O250 mmHg), when the fish changed from gill ventilation to air-breathing. increased significantly during gill ventilation compared to apnoea in aerated water through a significant increase in both f_H and V_S. P_CV and MCFP also increased significantly. During hypoxia, when the animals surface to ventilate air, we found a marked rise in f_H, P_CV, MCFP, and V_S, whereas P_DA decreased significantly. Simultaneous increases in P_CV and MCFP in aerated, as well as in hypoxic water, suggests that the venous system plays an important regulatory role for cardiac filling and V_S 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 P_CV and MCFP, whereas isoproterenol led to a marked decrease in P_CV, and tended to decrease MCFP. Thus, it is evident that stimulation of both - and ß-adrenoreceptors affects venous tone in S. marmoratus.

Key words: adrenergic regulation, air-breathing fish, cardiac filling, mean circulatory filling pressure, normoxia, hypoxia, venous return, venous tone, stroke volume, Synbranchus marmoratus

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