Substantial increases in cardiac output (CO), stroke volume (SV), and gastrointestinal blood flow are essential for euryhaline rainbow trout (Oncorhyncus mykiss) osmoregulation in seawater. However, the underlying hemodynamic mechanisms responsible for these changes are unknown. By examining a range of circulatory and cardiac morphological variables of seawater- and freshwater-acclimated rainbow trout, the present study revealed a significantly higher central venous pressure (CVP) in seawater-acclimated trout (~0.09 vs. -0.02 kPa). This serves to increase cardiac end-diastolic volume in seawater and explains the elevations in SV (~0.41 vs. 0.27 ml/kg) and CO (~21.5 vs. 14.2 ml·min-1·kg-1) when compared with trout in freshwater. Furthermore, these hemodynamic modifications coincided with a significant increase in the proportion of compact myocardium, which may be necessary to compensate for the increased wall tension associated with a larger stroke volume. Following a temperature increase from 10 to 16.5°C, both acclimation groups exhibited similar increases in heart rate (Q10 of ~2), but SV tended to decrease in seawater-acclimated trout despite the fact that CVP was maintained in both groups. This resulted in CO of seawater- and freshwater-acclimated trout stabilizing at a similar level after warming (~26 ml·min-1·kg-1). The consistently higher CVP of seawater-acclimated trout suggests that factors other than compromised cardiac filling constrained the SV and CO of these individuals at high temperatures. The present study highlights, for the first time, the complex interacting effects of temperature and water salinity on cardiovascular responses in a euryhaline fish species.

译文

心输出量 (CO),中风量 (SV) 和胃肠道血流量的显着增加对于海水中的虹鳟鱼 (Oncorhyncus mykiss) 渗透调节至关重要。然而,导致这些变化的潜在血液动力学机制尚不清楚。通过检查适应海水和淡水的虹鳟鱼的一系列循环和心脏形态变量,本研究表明,适应海水的鳟鱼的中心静脉压 (CVP) 明显更高 (〜0.09 vs. -0.02 kPa)。这有助于增加海水中的心脏舒张末期容积,并解释了与淡水中的鳟鱼相比,SV (〜0.41 vs.0.27毫升/kg) 和CO (〜21.5 vs.14.2毫升·min-1·kg-1) 的升高。此外,这些血液动力学改变与致密心肌比例的显着增加相吻合,这对于补偿与较大的中风量相关的壁张力增加可能是必要的。在温度从10 °C升高到16.5 °C之后,两个驯化组的心率均显示出相似的增加 (Q10为〜2),但是尽管在两个组中均维持了CVP,但在海水驯化的鳟鱼中SV趋于降低。这导致海水和淡水驯化鳟鱼的CO在变暖后稳定在相似的水平 (〜26毫升·min-1·kg-1)。适应海水的鳟鱼的CVP始终较高,这表明除心脏充盈受损以外的其他因素在高温下限制了这些个体的SV和CO。本研究首次强调了温度和水盐度对广盐鱼类心血管反应的复杂相互作用。

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