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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Venous hemodynamic responses to acute temperature increase in the rainbow trout (Oncorhynchus mykiss)

Department of Zoology, Göteborg University, Gothenburg, Sweden

Submitted 20 December 2006 ; accepted in final form 20 February 2007

Many ectotherms regularly experience considerable short-term variations in environmental temperature, which affects their body temperature. Here we investigate the cardiovascular responses to a stepwise acute temperature increase from 10 to 13 and 16°C in rainbow trout (Oncorhynchus mykiss). Cardiac output increased by 20 and 31% at 13 and 16°C, respectively. This increase was entirely mediated by an increased heart rate (f_H), whereas stroke volume (SV) decreased significantly by 20% at 16°C. The mean circulatory filling pressure (MCFP), a measure of venous capacitance, increased with temperature. Central venous pressure (P_ven) did not change, whereas the pressure gradient for venous return (MCFP-P_ven) was significantly increased at both 13 and 16°C. Blood volume, as measured by the dilution of ⁵¹Cr-labeled red blood cells, was temperature insensitive in both intact and splenectomized trout. This study demonstrates that venous capacitance in trout decreases, but cardiac filling pressure as estimated by P_ven does not change when cardiac output increases during an acute temperature increase. SV was compromised as f_H increased with temperature. The decreased capacitance likely serves to prevent passive pooling of blood in the venous periphery and to maintain cardiac filling pressure and a favorable pressure gradient for venous return.

cardiac performance; cardiac preload; stroke volume; venous capacitance; ⁵¹Chromium