Sesquiterpene lactones: Antispasmodic principles of the freshwater algae Hydrodictyon reticulatum

Hydrodictyon reticulatum is used in traditional medicine in Mexico to decrease gastrointestinal disorders suggesting that some of its chemical components have properties that relax smooth muscle. The hexane extract showed the most promising biological effects, with IC ₅₀ of 49.34 μg/ml in the spontaneous contraction of ileum. A detailed phytochemical analysis of the hexane extract led to the isolation of the known sesquiterpenes: β-Cayophyllene- 4,5-α-oxide (1) and two new sesquiterpene lactones, 3α,4α,8α-trihydroxy-10α-methoxy-1α,5α, 7α,11βH-guaia,6α, 12-olide (2) and 4α,8α-dihydroxy- 10α-methoxy-1α,5α,7α, 11-βH-guaia,6α,12- olide (3). The identification and characterization of these compounds were determined using 1-D and 2-D-NMR (through interpretation of NMR data). The antispasmodic activity of sesquiterpenes of H. reticulatum was studied on isolated tissue preparations from rabbit and rat intestine. The compounds at 1.79 at 3.44 × 10 ^-8 M doses reduced acetylcholine (Ach), histamine, and barium chloride-induced contractions on isolated rat ileum. Therefore, possess similar relaxant mechanism of action, in view of the fact that sesquiterpenes inhibit K ⁺-induced contraction and act through serotoninic, muscarinic, and histaminic receptors. So these data support that extract may interfere with calcium mobilization from intracellular stores or with calcium interaction with regular proteins or in the other steps in the calcium-signaling pathway.