PHARMACOLOGY OF HAEMAL VESSELS OF STICHOPUS CALIFORNICUS

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Abstract
The external haemal vessel of the holothurian Stichopus consists of an outer villous epithelium, circular muscle and connective tissue with regions of hemopoiesis. The vessel contracts rhythmically at about 5 per minute and the beat is inhibited by acetylcholine with a threshold concn. of the order of 10-14. Physostigmine potentiates the response to acetylcholine, while both nicotine and tetramethyl ammonium chloride inhibit the beat of the vessel. By analogy with the pharmacology of hearts, it is tentatively concluded that the Stichopus vessel is myogenic.