Calcium channel blockade as a target for the cardiovascular effects induced by the 8 (17), 12E, 14-labdatrien-18-oic acid (labdane-302)

The cardiovascular effects induced by labdane-302, a diterpene isolated from the stems of Xylopia langsdorffianna St. Hill and Tull, were evaluated in male Wistar rats. In normotensive, conscious animals, labdane-302 produced dose-dependent hypotension and tachycardia. These effects were significantly attenuated after pre-treatment with L-NAME (20 mg/kg, i.v.). In isolated mesenteric artery rings, labdane-302 (10− 10 – 10− 4 M) elicited concentration-dependent relaxation of phenylephrine-induced contractions (IC50 = 5.4 ± 1.4 μM). Endothelium removal, and pre-treatment with L-NAME (100 μM) or indomethacin (10 μM) caused significant reductions in sensitivity. Labdane-302 also caused concentration-dependent relaxation in arterial rings pre-contracted with high extracellular KCl (80 mM). In Ca2+-free depolarized preparations, labdane-302 inhibited contractions produced by cumulative increases in extracellular Ca2+ concentration. In GH3 cells, labdane-302 (100 μM) inhibited whole-cell L-type Ca2+ currents by ∼50%. These results demonstrate that labdane-302 causes hypotension through peripheral vasodilation, mediated in part by NO and PGI2 and by blockade of Ca2+ entry through L-type Ca2+ channels.