Submitted on November 23, 2008
Revised on January 14, 2009
Accepted on January 23, 2009
The role of venous capacitance, circulating catecholamines and heart rate in the hemodynamic response to increased temperature and hypoxia in the dogfish
Erik Sandblom1*, Georgina K Cox2, Steve F. Perry3, and Anthony P. Farrell2
1 Department of Zoology
2 University of British Columbia
3 University of Ottawa
* To whom correspondence should be addressed. E-mail: erik.sandblom{at}zool.gu.se.
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 sub-ambient central venous pressure (Pcv). Here, we explored venous hemodynamic responses to acute temperature increase and moderate (6.9 kPa) and severe (2.5 kPa) hypoxia in the dogfish (Squalusacanthias). Normoxic dogfish at 10°C had a Pcv between -0.08 and -0.04 kPa, and a mean circulatory filling pressure (Pmcf) of ~0.12 kPa. At 16°C, heart rate (fH), cardiac output (Q) and Pmcf increased, but Pcv and plasma adrenaline and noradrenaline levels were unchanged. In contrast, moderate and severe hypoxia increased Pcv, and decreased Q and stroke volume (VS). fH decreased in severe hypoxia, while Pmcf was unaffected despite elevated catecholamine levels. Atropine abolished hypoxic reductions in Q, VS and fH, but Pcv 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.
