A sensitive method for the assay of 5-hydroxytryptamine.

The movements of a strip of fundus from a rat stomach, suspended in a 5 ml. bath at 37 degrees , are recorded by a spring-loaded lever. The muscle is stretched for 15 to 30 sec. between contractions. 1 ng. 5-Hydroxytryptamine (5-HT), 10 ng. acetylcholine or 2 to 10 mug. of histamine all produce contractions, giving tracings about 4 cm. high. In the presence of hyoscine (10(-7)) low concentrations of 5-HT can be assayed directly from mixtures of the three substances. Sympathomimetic amines interfere with the assay, but this can be overcome. The preparation is robust, potentially suitable for use with an automatic assay apparatus and 10 to 100 times more sensitive than the rat uterus.