Willebrand factor in hemostasis in the in vitro bleeding time

Abstract

Heparinized porcine blood and plasma, at constant hydrostatic pressure, was allowed to flow through a 5-mm incision in a small piece of porcine skin. Changes in the exuded blood volume were measured, and the incision site was examined microscopically. When normal blood flowed through either normal or von Willebrand skin, the exuded blood volume decreased gradually and eventually stopped. Microscopic examination revealed a platelet plug in the incision site. This plug was positive for Willebrand factor when examined by immunofluorescence. In contrast, the blood from von Willebrand pigs continued to flow constantly, and a platelet plug was not seen. The delayed in vitro hemostasis in von Willebrand blood was corrected to the normal range by the addition of either normal plasma or partially purified Willebrand factor. Normal blood, in which the Willebrand factor was immunologically inhibited, showed delayed hemostasis. For this in vitro system, it appeared that plasmatic Willebrand factor played an essential role in hemostasis.

The role of Willebrand factor in platelet — blood vessel interaction, including a discussion of resistance to atherosclerosis in pigs with von Willebrand’s disease

“…These workers labelled platelets and Willebrand factor radioactively and their study suggested that Willebrand factor bound to the subendo thelium induced platelet adhesion and that it was the plasma protein alone that was necessary for normal platelet adhesion. Recent work in our own laboratory, with the use of a porcine system, is entirely consistent with these results (Bowie et al 1978;Kimura et al 1979).…”

“…This platelet -arterial wall interaction is enhanced by the von Willebrand factor in the plasma (Fass et al 1976a;Bowie et al 1978), platelets and the arterial wall (Jaffe et al 1974). The earlier discussion of our studies with the use of transfusions and in vitro bleeding time technique suggests that the level of Willebrand factor in the plasma plays an important role in this platelet -blood vessel interaction Kimura et al 1979). There is also evidence that adherence of platelets to the arterial surface in the normal animal may help to repair the endothelium and reduce its permeability (Gimbrone et al 1969;Wojcik et al 1969;Fry et al 1976;Reidy & Bowyer 1977).…”

“…[ 53 ] veloped a technique known as the ' in v i t r o ' bleeding time. A small skin is attached to the channel in the base of a flow cube, and heparinized porcine blood or plasma is allowed to flow through a 5 mm incision in the skin at a constant hydrostatic pressure The technique is described in detail by Kimura et al (1979)* The volume of blood or plasma exuding from the incision is measured and the incision site examined microscopically after haemostasis has occurred.…”