Maximum cardiac performance and adrenergic sensitivity of the sea bass Dicentrarchus labrax at high temperatures.

We examined maximum cardiac performance of sea bass Dicentrarchus labrax acclimated to 18 degrees C and 22 degrees C, temperatures near the optimum for growth of this species. Our aim was to study whether cardiac performance, especially the effect of adrenergic stimulation, differed when compared to salmonids. Sea bass and salmonids are both athletic swimmers but their cardiac anatomy differs markedly. The sea bass ventricle does not receive any oxygenated blood via a coronary circulation while salmonids have a well-developed arterial supply of oxygen to the compact layer of the ventricle. Using in situ perfused heart preparations, maximum cardiac performance of 18 degrees C-acclimated sea bass (i.e. cardiac output = 90.8+/- 6.6 ml min(-1) kg(-1) and power output = 11.41+/-0.83 mW g(-1)) was found to be comparable to that previously reported for rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta at similar temperatures and with tonic adrenergic (5 nmol l(-1) adrenaline) stimulation. For 22 degrees C-acclimated sea bass, heart rate was significantly higher, but maximum stroke volume was reduced by 22% (1.05+/-0.05 ml kg(-1)) compared with 18 degrees C (1.38+/- 0.11 ml kg(-1)). As a result, maximum cardiac output (99.4+/-3.9 ml min(-1) kg(-1)) was not significantly different at 22 degrees C. Instead, maximum power output was 27% higher at 22 degrees C (14.95+/-0.96 mW g(-1)) compared with 18 degrees C, primarily because of the smaller relative ventricular mass in 22 degrees C-acclimated sea bass. Compared with tonic adrenergic stimulation with 5 nmol l(-1) adrenaline, maximum adrenergic stimulation of the sea bass heart produced only modest stimulatory effects at both temperatures (12-13% and 14-15% increases in maximum cardiac output and power output, respectively, with no chronotropic effect). Adrenergic stimulation also increased the cardiac sensitivity to filling pressure, with the maximum left-shift in the Starling curve being produced by 50-100 nmol l(-1) adrenaline at 18 degrees C and 10-50 nmol l(-1) adrenaline at 22 degrees C. We show that the sea bass, which lacks a coronary arterial oxygen supply to the ventricle, has a powerful heart. Its maximum performance is comparable to a salmonid heart, as is the modest stimulatory effect of adrenaline at high temperature.