POSSIBLE MECHANISMS FOR THE EFFECTS OF RUSCUS EXTRACT ON MICROVASCULAR PERMEABILITY AND DIAMETER

The extract of Ruscus aculeatus is used in the treatment of venous ins ufficiency. In the present study, we used the hamster cheek pouch prep aration and investigated, in vivo, the effects of Ruscus extract and o f its combination with an alpha(1)- and alpha(2)-adrenergic receptor a ntagonists and a calcium blocker on (1) diameter of arterioles [intern al diameter (lD) range 10.0 to 70.0 mu m] and venules (TD range 20.0 t o 135.0 mu m) and (2) increased microvascular permeability induced by histamine. All these drugs were applied topically. For diameter measur ements, the preparations were placed under an intravital microscope co upled to a closed-circuit TV system. The TV monitor display was used t o obtain arteriolar and venular internal diameter recordings (always a t the same site) by an image shearing device. Ruscus extract elicited concentration dependent responses in the studied vessels: arterioles r emained unchanged in the concentration range tested while the venules remained unchanged or constricted depending on the concentration used. The observed venular constriction could be blocked by low concentrati ons (10(.9) M) of prazosin or diltiazem and by high concentrations (> 10(-6) M) of rauwolscine. For permeability measurements, 30 min after completion of the cheek pouch preparation, fluorescein-labelled dextra n (mel wt 150,000) was given intravenously. Histamine increased the nu mber of fluorescent vascular leakage sites from postcapillary venules - evidence for an increase in macromolecular permeability, which was q uantified in UV-light microscope as the number of leaky sites in the p repared area. Ruscus extract inhibited, in a dose-dependent fashion, t he macromolecular permeability-increasing effect of histamine.