Abstract
Cardiac cholinergic and adrenergic tones were determined in minimally instrumented African lungfish Protopterus annectens . Mean ±S.E. routine heart rate ( f H ) was 31·6 ± 1·4 beats min −1 , cholinergic tone was 34·6 ± 5·2% and adrenergic tone was 9·4 ± 2·3%, while the intrinsic f H after blockade of both adrenergic and cholinergic control systems was 39·1 ± 1·3 beats min −1 . It is demonstrated that routine cholinergic tone has probably been underestimated in previous studies on lungfishes, suggesting that withdrawal of vagal tone may provide an important mechanism to increase f H in this group of fishes during, for example, air breathing.