Alseis yucatanensis: a natural product from Belize that exhibits multiple mechanisms of vasorelaxation.

An aqueous extract of the bark of Alseis yucatanensis was studied to determine its mechanism of action in the relaxation of endothelium-denuded rat aortic tissues. The extract relaxed both norepinephrine (NE) and KCl-contracted vessels, with ED(50)'s of 0.12 and 1.73 mg/mL, respectively. In NE-contracted vessels, two phases of relaxation were evident which were separated in both time and dose range. At high concentrations, a rapid relaxation was seen that was due to the blocking of internal (ED(50)=0.49 mg/mL) and external (ED(50)=2.34 mg/mL) calcium channels. A second, slowly developing (i.e., long-term) relaxation to baseline was seen at lower concentrations. The time to complete relaxation was dose-dependent. This long-term response was not seen in KCl-contracted vessels, was prolonged by TEA, and could be reversed by the addition of KCl to the bath. These data suggest that the long-term relaxation is due to the opening of potassium channels.