Effects of drugs and nerve stimulation on the spleen and arteries of two species of dogfish, Scyliorhinus canicula and Squalus acanthias.

The effects of drugs and nerve stimulation on the spleen of 2 species of dogfish have been examined by experiments with perfused spleens and isolated spleen and artery strips. Adrenaline, noradrenaline and phenylephrine, acting via alpha adrenoceptors, constrict the perfused spleen of both species, thereby releasing erythrocytes, and contract the isolated spleen and artery strips. Phenotolamine competitively antagonizes the excitatory effects of adrenergic agonists. The responses of the spleen to acetylcholine are very irregular, and a rapid desensitization makes evaluation of the mode of action of this drug difficult. In the artery strips acetylcholine produces a dose-dependent contraction. Fluorescent histochemistry reveals well developed adrenergic innervation of the arteries, and a few adrenergic terminals in the spleen. Stimulation of splenic nerves produces normally splenoconstriction in Squalus, which can be blocked by phentolamine but not by atropine. The nervous control of the Scyliorhinus spleen seems to be poor or lacking. It is concluded that the dogfish spleen, and maybe also the arteries, are to a large extent controlled by circulating catecholamines and (in Squalus) also by sympathetic adrenergic fibres.