Cholinergic and adrenergic influences on the heart of the African lungfish Protopterus annectens
Cardiac cholinergic and adrenergic tones were determined in minimally instrumented African lungfish Protopterus annectens. Mean ±S.E. routine heart rate (fH) 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 fH 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 fH in this group of fishes during, for example, air breathing.