Relaxing Activity of Two Linear Diterpenes from Cystoseira brachycarpa var. balearica on the Contractions of Intestinal Preparations

Abstract

Eleganolone (1) and elegandiol (2), two linear diterpenes isolated from Cystoseira brachycarpa var. balearica, were tested on guinea-pig intestinal preparations. Both these compounds inhibited the contractile activities of acetylcholine (Ach) and histamine (Hist) on ileum musculature; the relative pIC₅₀ values of eleganolone were found to be 4.60 ± 0.03 and 4.84 ± 0.20, respectively, while those of elegandiol were 4.71 ± 0.18 and 5.18 ± 0.01, respectively. Furthermore, 1 and 2 dose-dependently relaxed the same preparations precontracted with 300 µM BaCl₂(pIC₅₀ = 4.34 ± 0.18 for 1 and pIC₅₀ = 4.34 + 0.02 for 2) or with 60 mM KCl (pIC₅₀ = 4.73 ± 0.18 and 4.47 ± 0.06, respectively). On colon smooth muscle, the diterpenes inhibited the spontaneous contractile tone and this effect was reversed by both methylene blue (3 × 10^-6M) and haemoglobin (3 × 10^-6M). Tetraethylammonium (TEA), furosemide, N _ω-nitro L-arginine methyl ester (L-NAME), indomethacin, α-chymotrypsin, and metoprolol were unable to block the eleganolone and elegandiol relaxing action on colonic musculature, but rather potentiated this response. On the contrary, the β₂-blocker butoxamine partially inhibited the diterpenes activity. These results suggest that Cystoseira diterpenes act at a second messenger cyclase system rather than at a receptor level.

Key words

Cystoseira brachycarpa var. balearica - Cystoseiraceae - brown algae - diterpenoids - relaxing activity