Abstract
Five compounds, 3,4’-dihydroxy-3’,5,5’-trimethoxydihydrostilbene, 1, 3,4'-dihydroxy-3',5'-dimethoxydihydrostilbene, 2, 3,4'-dihydroxy-5,5'-dimethoxydihydrostilbene, 3, 9,10-dihydro-2,7-dihydroxy-4,6-dimethoxyphenanthrene, 4, and the previously unreported 1,2,6,7-tetrahydroxy-4-methoxyphenanthrene, 5, were isolated from the South American orchid, Brasiliorchis porphyrostele. An in depth analysis of their vascular effects was performed on in vitro rat aorta rings and tail main artery myocytes. Compounds 1-4 were shown to possess vasorelaxant activity on rings pre-contracted by the α1 receptor agonist phenylephrine, the CaV1.2 stimulator (S)-(-)-Bay K 8644, or depolarised with high K+ concentrations. However, compound 5 was active solely on rings stimulated by 25 mM but not 60 mM K+. The spasmolytic activity of compounds 1 and 4 was significantly affected by the presence of an intact endothelium. The KATP channel blocker glibenclamide and the KV channel blocker 4-aminopyridine significantly antagonised the vasorelaxant activity of compounds 4 and 1, respectively. In patch-clamp experiments, compounds 1-4 inhibited Ba2+ current through CaV1.2 channels in a concentration-dependent manner, whereas neither compound 4 nor compound 1 affected K+ currents through KATP and KV channels, respectively. The present in vitro, comprehensive study demonstrates that Brasiliorchis porphyrostele may represent a source of vasoactive agents potentially useful for the development of novel antihypertensive agents that has now to be validated in vivo in animal models of hypertension.