Stimulation of endogenous fibrinolytic activity occurs after IPC, both in normal subjects and postthrombotic patients; however, baseline and overall fibrinolytic response in postthrombotic patients is reduced. The mechanism of increased fibrinolytic activity is likely because of a reduction in PAI-1, with a resulting increase of tPA activity.

Summary.  We have reported on a patient with thrombocytopenia, impaired platelet aggregation, secretion, phosphorylation of pleckstrin and myosin light chain (MLC), and GPIIb–IIIa activation, associated with a heterozygous mutation in transcription factor CBFA2 (core binding factor A2, RUNX1 or AML1). To obtain insights into the abnormal platelet mechanisms and CBFA2‐regulated genes, we performed platelet expression profiling in four control subjects and the patient using the Affymetrix U133 GeneChips. In the patient, 298 probe sets were significantly downregulated at least 2‐fold. MLC regulatory polypeptide (MYL9 gene) was decreased ∼77‐fold; this is an important finding because agonist‐stimulated MLC phosphorylation is decreased in patient platelets. Genes downregulated ≥ 5‐fold include those involving calcium binding proteins (CABP5), ion transport (sodium/potassium/Ca exchanger, SLC24A3), cytoskeletal/microtubule proteins (erythrocyte membrane protein band 4.1‐like 3, EPB41L3; tropomyosin 1, TPM1; tubulin, alpha 1, TUBA1), signaling proteins (RAB GTPase activating protein 1‐like, RABGAP1L; β3‐endonexin, ITGB3 BP) and chemokines (platelet factor 4 variant 1, PF4V1; chemokine CXCL5, CXCL5). These and other downregulated genes are relevant to the patient's platelet defects in function and production. These studies provide the first proof of concept that platelet expression profiling can be applied to obtain insights into the molecular basis of inherited platelet defects.

G proteins play a major role in signal transduction upon platelet activation. We have previously reported a patient with impaired agonist-induced aggregation, secretion, arachidonate release, and Ca 2؉ mobilization. Present studies demonstrated that platelet phospholipase A 2 (cytosolic and membrane) activity in the patient was normal. Receptormediated activation of glycoprotein (GP) IIb-IIIa complex measured by flow cytometry using antibody PAC-1 was diminished despite normal amounts of GPIIb-IIIa on platelets. Ca 2؉ release induced by guanosine 5-[␥-thio]triphosphate (GTP[␥S]) was diminished in the patient's platelets, suggesting a defect distal to agonist receptors. GTPase activity (a function of ␣-subunit) in platelet membranes was normal in resting state but was diminished compared with normal subjects on stimulation with thrombin, platelet-activating factor, or the thromboxane A 2 analog U46619. Binding of 35 S-labeled GTP[␥S] to platelet membranes was decreased under both basal and thrombin-stimulated states. Iloprost (a stable prostaglandin I 2 analog) -induced rise in cAMP (mediated by G␣ s ) and its inhibition (mediated by G␣ i ) by thrombin in the patient's platelet membranes were normal. Immunoblot analysis of G␣ subunits in the patient's platelet membranes showed a decrease in G␣ q (<50%) but not G␣ i , G␣ z , G␣ 12 , and G␣ 13 . These studies provide evidence for a hitherto undescribed defect in human platelet G-protein ␣-subunit function leading to impaired platelet responses, and they provide further evidence for a major role of G␣ q in thrombin-induced responses.

SummaryTo examine the impact of the underlying defective platelet mechanism on the response to 1-desamino-8-D-arginine vasopressin (DDAVP, Desmopressin), we studied the effect of intravenous infusion of 0.3 μg/kg of DDAVP in a randomized double blind placebo-controlled trial with cross-over in 18 carefully characterized patients with congenital platelet defects (CPD) and BT ≥9 min. Eleven patients had normal dense granule stores and normal thromboxane A2 (TxA2) production (Group I), 3 patients had normal granule stores but impaired TxA2 production (Group II), and 4 had δ-storage pool deficiency (Group III). DDAVP shortened BT at 50 min (DDAVP 14.6 ± 2.2 vs placebo 19.6 ± 2.3 min; n = 18; mean ± SE; p = 0.003) and 4h (17.0 ± 2.2 vs 19.6 ±2.1 min, p = 0.055), and raised plasma FVIIIC and von Willebrand factor (vWF). At 50 min DDAVP shortened BT by ≥5 min in 8 of 11 Group I patients (mean 9.7 ± 1.3 vs 16.3 ± 2.8 min; p <0.008), 1 of 3 Group II patients (11.9 ± 3.9 vs 17.7 ± 6.6; p = NS) and none of Group III patients (mean 30 min both arms). Ten patients (Group I or II) were managed successfully during surgical procedures with DDAVP alone. We conclude that DDAVP shortens BT in majority of CPD patients with normal dense granule stores and suggest that BT response may be dependent on the underlying platelet defect. DDAVP is a useful modality in management of selected patients, particularly those with normal dense granule stores.

The hypothesis that heparin-coated perfusion circuits reduce thrombin formation and activity; fibrinolysis; and platelet, complement, and neutrophil activation was tested in 20 consecutive, randomized adults who had cardiopulmonary bypass. Twenty identical perfusion systems were used; in 10, all blood-contacting surfaces were coated with partially degraded heparin (Carmeda process; Medtronic Cardiopulmonary, Anaheim, Calif.). All patients received a 300 U/kg dose of heparin. Activated clotting times were maintained longer than 400 seconds. Cardiopulmonary bypass lasted 36 to 244 minutes. Blood samples for platelet count, platelet response to adenosine diphosphate, plasma beta-thromboglobulin, inactivated complement 3b, neutrophil elastase, fibrinopeptide A, prothrombin fragment F1.2, thrombin-antithrombin complex, tissue plasminogen activator, plasminogen activator inhibitor-1, plasmin alpha 2-antiplasmin complex, and D-dimer were obtained at these times: after heparin was given, 5 and 30 minutes after cardiopulmonary bypass was started, within 5 minutes after bypass was stopped, and 15 minutes after protamine was given. After cardiopulmonary bypass, tubing segments were analyzed for surface-adsorbed anti-thrombin, fibrinogen, factor XII, and von Willebrand factor by radioimmunoassay. Heparin-coated circuits significantly (p < 0.001) reduced platelet adhesion and maintained platelet sensitivity to adenosine diphosphate (p = 0.015), but did not reduce release of beta-thromboglobulin. There were no significant differences between groups at any time for fibrinopeptide A, prothrombin fragment F1.2, or thrombin-antithrombin complex or in the markers for fibrinolysis: D-dimer, tissue plasminogen activator, plasminogen activator inhibitor-1, and alpha 2-antiplasmin complex. In both groups, concentrations of prothrombin fragment F1.2 and thrombin-antithrombin complex increased progressively and significantly during cardiopulmonary bypass and after protamine was given. Concentrations of D-dimer, alpha 2-antiplasmin complex, and plasminogen activator inhibitor-1 also increased significantly during bypass in both groups. Fibrinopeptide A levels did not increase during bypass but in both groups increased significantly after protamine was given. No significant differences were observed between groups for levels of inactivated complement 3b or neutrophil elastase. Radioimmunoassay showed a significant increase in surface-adsorbed antithrombin on coated circuits but no significant differences between groups for other proteins. We conclude that heparin-coated circuits used with standard doses of systemic heparin reduce platelet adhesion and improve platelet function but do not produce a meaningful anticoagulant effect during clinical cardiopulmonary bypass. The data do not support the practice of reducing systemic heparin doses during cardiac operations with heparin-coated extracorporeal perfusion circuitry.