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 microM 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 x 10(-6) M) and haemoglobin (3 x 10(-6) M). Tetraethylammonium (TEA), furosemide, N omega-nitro-L-arginine methyl ester (L-NAME), indomethacin, alpha-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 beta 2-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.

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