Adrenergic and cholinergic effects on the heart, the lung and the spleen of the African lungfish, Protopterus aethiopicus.

Abstract

Effects of adrenergic and cholinergic drugs were studied on isolated preparations from the heart, the lung and the spleen of the African lungfish. In addition, a nerve-lung preparation was employed for the study of the autonomic nervous control of the lung. Falck-Hillarp fluorescent histochemistry was used in the search for adrenergic neurons in the sympathetic chain and tissues. The Protopterus lung received a cholinergic excitatory innervation via the pulmonary branches of the vagi. The presence of parasympathetic ganglia in the lung tissue is indicated. Adrenergic drugs, when producing a response, either contracted or relaxed lung strips. Spleen strips were contracted by cholinergic drugs acting on muscarinic receptors and, to a lesser extent, by adrenergic drugs. A strong negative inotropic effect was produced by carcachol on paced atrial but not ventricular strips, while adrenaline increased the contraction force in ventricular but not atrial strips. The sympathetic ganglion cells did not contain enough catecholamines to give off any visible fluorescence, nor was it possible to show any adrenergic nerve terminals in the tissues studied. It is concluded that the adrenergic control in the lungfish is mainly due to circulating catecholamines, rather than adrenergic nerve fibres, since concentrations of catecholamines in protopterus plasma are high enough to affect the spleen, lung and ventricle.