Comparative effects on TXA2 biosynthesis of products extracted from Lippia multiflora Moldenke leaves

The effects of the total phenolic extract (TPLi) from Lippia multiflora leaves and of its 2 main components i.e. Verbascoside (VLi) and Lil on TXA2 biosynthesis were studied. TXA2 biosynthesis was induced by incubation of arachidonic acid with horse platelet microsomes (HPM), TXB2, a stable metabolite of TXA2, was determined by using RIA. Under the experimental conditions adopted, Verbascoside did not significantly modify TXA2 biosynthesis. On the contrary, the total phenolic extract and Lil both inhibited TXA2 biosynthesis. Their action was dose-related, Lil being the more potent. The ID50 were 1.19 +/- 0.08 mg/ml and 10.64 +/- 0.64 mg/ml for Lil and total phenolic extract respectively. The study of regression curves representing the hypotensive action and the anti-thromboxane synthetase activity versus log(dose) of TPLi and Lil suggested that Lil would likely be responsible for the TPLi hypotensive action. Its antithromboxane synthetase activity could be considered as a major contributor to the mechanism of this effect.