Evidence for the absorption and synthesis of 5-hydroxytryptamine in perfused muscle and intestinal tissue and whole worms of adult Ascaris suum.

The metabolites of 5-hydroxytryptamine (5-HT, serotonin) namely, L-tryptophan, 5-hydroxytryptophan, 5-hydroxyindole acetic acid and 5-hydroxytryptophol were measured in perfused tissue and whole worms from adult female Ascaris suum using reversed-phase liquid chromatography with electrochemical detection. The intracellular levels of each metabolite were quantitated in response to several physiological effectors but only L-tryptophan (TRP) caused dose-dependent changes in these metabolites. Serotonin itself could also be absorbed by perfused A. suum muscle and intestinal tissue. When live A. suum were tied at the anterior and posterior regions to restrict TRP absorption by the intestine, TRP was absorbed through the cuticle and converted into 5-HT by the muscle tissue. In united live parasites TRP absorption was observed in both muscle and intestinal tissue. Collectively, the data indicated that 5-HT may be either absorbed directly or synthesized de novo from absorbed TRP in the isolated tissue of A. suum. The 5-HT, in the adult female A. suum, can be synthesized de novo from TRP, or 5-HT can be absorbed from the environment both through the cuticle and by the intestine of living parasites. Data also indicated that there was preferential sequestering of 5-HT and the metabolites of 5-HT in the anterior tissues of the worms.