Cholinergic and adrenergic tone on the heart of the Antarctic dragonfish, Gymnodraco acuticeps, living at sub-zero temperatures

Heart rate and ventral aortic blood pressures were recorded from the Antarctic dragonfish,Gymnodraco acuticeps, a member of the family Bathydraconidae. At −1.0 °C, the resting heart rate was 17.4 beats per minute and the ventral aortic pressure was 3.4 kPa. Cholinergic and adrenergic tone on the heart was determined by administration of the muscarine and ß-adrenoreceptor antagonists, atropine and sotalol, respectively. Neither antagonist influenced ventral aorta blood pressure; however, injection of atropine resulted in a significant increase in heart rate, and sotalol a decrease in heart rate. The cholinergic tone accounted for 30% of intrinsic heart rate and the adrenergic tone 26% of intrinsic heart rate. Comparison of these cardiac data with those for other teleosts from a wide range of thermal environments revealed no significant correlation for either cholinergic or adrenergic tone with body temperature (i.e. thermal independence); however, the resting and intrinsic heart rate of teleosts were strongly correlated with temperature.