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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

The role of venous capacitance, circulating catecholamines, and heart rate in the hemodynamic response to increased temperature and hypoxia in the dogfish

¹Faculty of Land and Food Systems and ²Department of Zoology, University of British Columbia, Vancouver, British Columbia; and ³Department of Biology, University of Ottawa, Ottawa, Ontario, Canada

Submitted 23 November 2008 ; accepted in final form 23 January 2009

Hypoxia and increased temperature alter venous blood pressures in teleosts through active changes in venous tone. Elasmobranchs possess a capacious venous system but have limited adrenergic vascular innervation and subambient central venous pressure (P_cv). In this study, we explored venous hemodynamic responses to acute temperature increase and moderate (6.9 kPa) and severe (2.5 kPa) hypoxia in the dogfish (Squalus acanthias). Normoxic dogfish at 10°C had a P_cv between –0.08 and –0.04 kPa and a mean circulatory filling pressure (P_mcf) of 0.12 kPa. At 16°C, heart rate (f_H), cardiac output (Q), and P_mcf increased but P_cv and plasma epinephrine and norepinephrine levels were unchanged. In contrast, moderate and severe hypoxia increased P_cv and decreased Q and stroke volume (V_S). f_H decreased in severe hypoxia, whereas P_mcf was unaffected despite elevated catecholamine levels. Atropine abolished hypoxic reductions in Q, V_S, and f_H, but P_cv still increased. In contrast to the response in teleosts, this study on dogfish suggests that venous capacitance changes associated with warming and hypoxia are minimal and likely not mediated by circulating catecholamines. Thus hemodynamic status of the capacious elasmobranch venous circulation is potentially regulated by blood volume shifts from passive flow-mediated events and possibly through myogenic mechanisms.

cardiac filling; cardiac performance; elasmobranch; mean circulatory filling pressure