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

摘要

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 (Pcv). 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 Pcv between -0.08 and -0.04 kPa and a mean circulatory filling pressure (Pmcf) of ～0.12 kPa. At 16°C, heart rate (f H), cardiac output (Q), and Pmcf increased but P cv and plasma epinephrine and norepinephrine levels were unchanged. In contrast, moderate and severe hypoxia increased Pcv and decreased Q and stroke volume (VS). fH decreased in severe hypoxia, whereas Pmcf was unaffected despite elevated catecholamine levels. Atropine abolished hypoxic reductions in Q, VS, and fH, 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. Copyright ? 2009 the American Physiological Society.