Adenosine-1 active ligands: Cirsimarin, a flavone glycoside from Microtea debilis

Several plants collected through different approaches were screened on distinct receptors using ligand-binding studies as bioassay. Extracts of Microtea debilis showed high activity on adenosine A(1) receptors. Bioassay-guided fractionation using ligand-binding studies resulted in the isolation of an adenosine A(1) active ligand, cirsimarin (cirsimaritin 4'-O-glucoside). GTP did not influence the radioligand inhibition curve of cirsimarin, indicating that this compound is acting as an antagonist at the adenosine-A(1) receptors. The use of this plant against ''proteinuria'' in traditional medicine in Suriname (South America) may be explained by the adenosine A(1) antagonistic action of cirsimarin. A series of flavonoids was tested in the same assay, but they were less active. No structure-activity relationship could be observed.