AUTONOMIC NERVOUS TONE AND REGULATION OF HEART-RATE IN THE GOLDFISH, CARASSIUS-AURATUS

1. Heart rate regulation in resting and exercising goldfish was investigated by pharmacological blockade of cardiac autonomic fibers in unrestrained goldfish. 2. In resting fish, atropine (1 mg/kg) elicits rapid rate increases averaging 110%; subsequent injection of propranolol (1 mg/kg), but not phentolamine (2 mg/kg), reduces heart rate. 3. Propranolol decreases heart rate and blocks the full atropine-induced increase, while phentolamine does not. 4. Calculated sympathetic tone (as % intrinsic heart rate) was 22% at 20-25°C; parasympathetic tone was 66%. 5. Enforced swimming (1.5 BL/sec) induces rapid cardioacceleration, which is abolished by propranolol. 6. Fluorescence histochemistry reveals adrenergic innervation of the muscular walls of all heart chambers. 7. An active role for the sympathetic nervous system in cardiovascular adjustments for exercise is suggested. © 1979.