The effect of an acute temperature increase on the control of the heart of the Antarctic teleost Pagothenia borchgrevinki was examined. Heart rate was thermally independent over the range –1.2°C to 3°C, although increasing the temperature from –1.2°C to 3°C elicited a decrease in ventral aortic pressure. Administration of the muscarinic receptor antagonist atropine and the -adrenoreceptor antagonist sotalol abolished the thermal independence of heart rate, with heart rate increasing at Q 10 =2. As temperature was increased from –1.2°C to 3°C, cholinergic tone on the heart also increased, from 44.6±4.2% to 70.0±8.4%. At the same time the adrenergic tone increased from 35.5±3.3% to 43.0±3.1%, but the effect on the heart was masked by the increase of cholinergic tone, leading to the thermal independence of heart rate.

• Constancy and control of heart rate during an increase in temperature in the Antarctic fish Pagothenia borchgrevinki