ATA is a novel anticoagulant polymeric anionic aromatic compound that inhibits von Willebrand factor binding to platelet glycoprotein Ib and thereby prevents ristocetin- and shear stress-induced platelet aggregation. To investigate its mechanism of action, ATA fractions of homogeneous M(r) have been prepared by size exclusion chromatography. ATA fractions of M(r) > or = 2,500 are most effective at inhibiting vWF-mediated platelet aggregation, and ATA of M(r) = 2,500 also inhibits thrombin-induced platelet activation. Paradoxical results were observed in studies of ATA with M(r) = 6,400. This fraction of ATA stimulates aggregation of washed platelets or platelet-rich-plasma. The dose/response of aggregation shows a bell-shaped curve with maximal aggregation at approximately 2 micrograms/ml. Platelet aggregation is associated with phosphoinositide turnover and protein kinase C- and calcium-dependent protein phosphorylation. Platelet signalling responses to ATA are inhibited by platelet pretreatment with PGI2 or dibutyryl-cyclic AMP, but are unaffected by inhibiting platelet cyclooxygenase with aspirin. These results suggest that M(r) 6,400 ATA directly activates platelet phospholipase C to initiate platelet aggregation. This effect, unique to M(r) 6,400 ATA, could potentially mitigate ATA's beneficial anti-thrombotic effect on vWF-mediated platelet responses, and should be considered when analyzing results of experiments that utilize unfractionated ATA.

The effectiveness of prophylactic desmopressin acetate in reducing hemorrhage after cardiopulmonary bypass operations is controversial. We conducted a prospective, randomized, placebo-controlled, double-blind trial to determine its effectiveness and safety in such patients. Eighty-three evaluable patients undergoing valvular heart operations were randomized to receive desmopressin (0.3 microgram/kg) (41) or placebo (42) after cardiac bypass. Demographic characteristics were similar in both groups. There was no significant difference in total 24-hour blood loss between groups (desmopressin 1064.8 +/- 647.1 ml versus placebo 844.4 +/- 507.6 ml; p greater than 0.05), or in the requirement for red blood cell, platelet, or fresh frozen plasma transfusion, or for reexploration for control of hemorrhage. Neither was there a difference in the occurrence of thrombotic complications between groups. Analysis of factor VIII activity, von Willebrand factor, or von Willebrand factor multimers failed to show significant correlations with blood loss or differences between groups except for factor VIII activity, which was significantly higher in the desmopressin group 1 hour after operation than in the placebo group. A detailed comparative analysis of similar trials to determine the reasons for different outcomes suggests that desmopressin should not be used routinely as a prophylactic agent to reduce postsurgical hemorrhage, but that it may be beneficial when used in patients who already manifest excessive bleeding postoperatively.

Fibrinogen, purified by β-alanine precipitation, was examined by two analytical techniques to determine the distribution of polypeptides responsible for the molecular weight heterogeneity of this material. In the first procedure fibrinogen was resolved by electrophoresis on a large pore sodium dodecyl sulfate (SDS) gel into two major bands, [ and ]I, Mr = 3.5 × 105 and 3.1 × 105. Polypeptides comprising fibrinogen in bands I and II were examined on a second SDS gel after reduction and electrophoresis of gel slices containing these two bands. Fibrinogen in band I included, in addition to the Bβ and γ chains, two major molecular weight forms of Aα chain, Aα/1 and Aα/Z, Mr = 7 × 104 and 6.7 × 104 respectively. Fibrinogen in band II contained in addition to Aα/1 and 2, a number of Aα chains, primarily Aα/6–101 Mr = 3–4 × 104 less than Aα/1.

A new method for the quantification of factor-VIII protein in plasma is described which utilizes only commercially available equipment and material. The procedure involves separation of factor VII from other plasma proteins by a two-stage sodium dodecyl sulphate gel electrophoretic technique and quantification of the protein by scanning densitometry. The plasma from normal individuals, haemophiliacs, obligate carriers of haemophilia and patients with von Willebrand's disease have been examined by this technique. In general, the data support the earlier findings obtained by quantitative immunoelectrophoresis. In addition, some abnormalities not detected by immunoelectrophoresis are observed by the gel electrophoresis technique.

A new method has been described for the isolation of factor VIII. The method results in a high yield of factor VIII that is homogeneous by several different criteria. The purified protein is very stable and is not dissociated in the presence of 1 M NaCl or 0.25 M CaCl2. The highly purified protein is readily activated and inactivated by various proteolytic enzymes, such as thrombin, plasmin, and trypsin. The molecular events that lead to the activation reaction, however, have not been established.