Multiwire area X-ray diffractometers.

We have studied a young male with lactoferrin deficiency and a bleeding tendency responsive to cryoprecipitate. This child has had increased bleeding following surgical procedures and a variably prolonged template bleeding time. The patient has a normal platelet count, normal in vitro platelet ATP secretion and aggregation in response to a variety of agonists, and normal concentration of plasma-von Willebrand factor ristocetin cofactor activity and antigen. Analysis of plasma-vWf multimers by agarose gel electrophoresis consistently demonstrated a subtle decrease in the largest vWf multimers. In contrast, analysis of the patient's platelet-vWf revealed normal vWf:Ag, decreased vWf ristocetin cofactor activity, and a striking absence of the high and intermediate size molecular weight vWf multimers. Analysis of surface bound platelet-vWf demonstrated normal amounts on the surface of unstimulated platelets, but after thrombin stimulation the platelet-vWf surface expression did not increase. This lack of increased platelet-vWf surface expression resulted from decreased binding of secreted platelet-vWf to be surface of stimulated platelets. These data suggest that the patient's bleeding tendency may be related to a defect in his platelet-vWf structure and/or mobilization. This case represents a unique demonstration of an abnormality of platelet-vWf in the presence of normal plasma-vWf, and supports the data indicating an important role for platelet-vWf in primary hemostasis.

Biopolymers↗

PubMed1992

In vivo experiments indicate that relatively high platelet deposition in von Willebrand's disease 'Vicenza' is caused by normal platelet-VWF levels rather than by high VWF-multimers in plasma.

Von Willebrand's disease (vWD) 'Vicenza' is characterized by low plasma von Willebrand Factor antigen (vWF:Ag) and very low levels of Ristocetin Cofactor activity (RiCof). The hemorrhagic tendency in vWD 'Vicenza' is, however, mild and bleeding times in this rare vWD-subtype are only slightly prolonged (1). Larger than normal multimers of plasma-vWF and normal levels of platelet-vWF have both been suggested to compensate the defects that are normally present in vWD. To elucidate the mechanisms involved, whole blood of four patients with vWD 'Vicenza' was circulated through a rectangular perfusion chamber (2) with fibrillar collagen as adhesive surface. Under these conditions, both plasma and platelet vWF participate to platelet adhesion. Compared to perfusion results with blood of normal donors, platelet adhesion of 'Vicenza' patients was decreased. However, the Vicenza defect was less than was observed in parallel experiments with blood of vWD type 1 subtype platelet-low patients and blood of a severe vWD patient. Adhesion was not increased in perfusions with only plasma of the 'Vicenza' vWD-patients. Equal vWF:Ag concentrations of normal multimeric composition were just as effective as the high multimeric 'Vicenza' vWF. Therefore, the abnormal plasma-vWF in 'Vicenza' patients does not cause the relatively high adhesion obtained with whole blood. In contrast, platelets of vWD 'Vicenza' patients resuspended in human albumine solution (HAS) showed far better adhesion than (vWF-poor) platelets of a patient with severe vWD. The values were at least comparable and tended to be higher than those obtained with normal platelets or with platelets of patients with vWD type I subtype platelet normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Biopolymers↗