Microhemorrhagic maculopathy

Twenty subjects, 12 males and eight females aged 14 to 58 years, had a small monocular macular hemorrhage that was punctate, round, or bilobed and seemed to originate from the perifoveal capillary plexus. Although clinical study results failed to establish a common causal denominator, three of the 20 patients had a history of preceding increased venous pressure (Valsalva stress), three of nine subjects tested showed impaired blood platelet aggregation, and an additional four of 20 were taking medications known to impair platelet function both in vitro and in vivo. Macular microhemorrhages resolve spontaneously, and available data suggest that the syndrome is benign.

Platelet consumption and sequestration in severe acute respiratory failure

To evaulate alterations in platelek kinetics and organ sequestration patterns during acute lung injury, we studied the fate of autologous radiolabeled platelets in 15 patients with severe acute respiratory failure (ARF) of diverse etiology. Thrombocytopenia (< 100,000 platelets/microliters) occurred in 10 patients. Platelet lifespan was reduced (2.30 +/- 0.39 days; mean +/- SEM) compared with normal volunteers (6.29 +/- 0.69; p < 0.01). Platelet turnover rate during ARF (251,100 +/- 90,000 platelets/microliters x day) was twice normal and never below the normal range. Platelet sequestration, determined by surface scintillation counting, occurred in the lungs, liver, and spleen. Although our measurements in patients with severe ARF did not determine whether platelets cause or exacerbate acute lung disease, the increased platelet consumption and pulmonary sequestration we detected suggests that platelets are directly involved in the pathophysiology of acute lung injury.

Platelet function and platelet lipid composition in the dyslipoproteinemias

Blood platelets from eight patients with hyperbetalipoproteinemia (type II) were more reactive to aggregating agents in vitro than those of 13 type IV patients or 12 normal subjects. Platelets of two patients with abeta-lipoproteinemia were also slightly hyperreactive in comparison with normal platelets. However, in one patient with Tangier disease the platelets were distinctly hyporeactive to aggregating agents. Total platelet phospholipid concentration (PL) was elevated in the four groups of patients studied but was highest in the platelets of type IV patients. Platelet-free cholesterol (FC) was significantly higher than normal in all of the dyslipoproteinemias studied. The FC was highest in the two patients with abetalipoproteinemia. The FC/PL molar ratio was normal in all but the abeta-lipoproteinemic patients, in whom it was markedly elevated. Therefore, there is no apparent correlation between FC/PL molar ratio and platelet behavior in vitro. Analysis of individual platelet phospholipids in the four patient groups showed that platelets in Tangier disease had very low concentrations of lysolecithin and phosphatidylinositol (PI) in comparison with normal platelets and the other disease states. Our findings suggest that lysolecithin and phosphatidylinositol may be involved in the structure or function of the sites which modulate platelet response to aggregating agents.

Bleeding time in uremia: a useful test to assess clinical bleeding

Modified Ivy bleeding time (template) and platelet aggregation to ADP, epinephrine, and collagen were studied in 26 uremic patients who had not recently ingested anti-platelet drugs. Regardless of the aggregating agent used, the abnormalities in platelet aggregation were often mild, even with advanced uremia, and frequently less severe than the effects of common anti-platelet drugs. The inhibition of collagen-induced aggregation was significantly correlated with both increased bleeding time and blood urea nitrogen. Platelet aggregation was not discriminative between clinically bleeding and non-bleeding groups of patients, but the bleeding time was helpful in this regard. In certain cases, the aggregometric patterns differed between drug-induced and uremic thrombocytopathies. Platelet aggregometry appears to be of little help clinically in assessing the severity of the uremic bleeding diathesis.

Type IV and type "A-B" collagens do not elicit platelet aggregation or the serotonin release reaction

Human collagens were isolated from kidney, lung, skin, aorta, cartilage, and placenta. Five different types were obtained, including two new molecular species, one characteristic of basement membranes, or type IV collagen, and the other the recently described "A-B" collagen derived from fetal membranes. All the collagens were purified and separated by combination of heat-gelation fractionation and salt fractionation. In neutral solution at 37 degrees neither type IV nor type "A-B" collagen elicited platelet aggregation or 14C-serotonin release. Preincubation of platelets with both types IV and "A-B" collagen did not inhibit aggregation upon subsequent addition of collagen types I, II, or III.

Platelet function abnormalities in a family with recurrent arterial thrombosis

Three young family members with recurrent arterial thrombosis underwent investigation for lipid or coagulation abnormalities. Lipoprotein electrophoresis, cholesterol, triglyceride levels, and routine coagulation studies were unremarkable. By contrast, testing of platelet function showed enhanced platelet aggregability to epinephrine and collagen in two of the subjects. In addition, release of 14C-serotonin by adenosine diphosphate and epinephrine was increased over control values in these same two patients. The third subject demonstrated decreased platelet aggregation and lowered 14C-serotonin release, but was symptomatic with rest pain at the time of testing. The ongoing in vivo thrombosis in the third subject may account for hypocoagulable platelets by in vitro testing. These abnormally sensitive platelets identified by platelet function testing may be associated with a familial "hypercoagulability" syndrome. Definition of the hemostatic abnormality in these individuals provided a rational basis for pharmacological therapy with antiplatelet drugs, which appeared to be successful.

Pilot epidemiological studies in thrombosis

Some differences in the blood of farmers in Nurmijarvi, Finland, Canino, Italy, and Beltsville, Maryland in the United States apparently were associated with differences, among the areas, in the farmers' diets. Those associations suggested that diets that are high in saturated fats (Nurmijarvi) could predispose humans to develop intravascular disease. Such predisposition has been observed in experimental animals. Low levels of the parameters that are considered active in such predisposition apparently were associated with diets that were low in saturated fats (Canino) or with diets that were low in saturated and high in unsaturated fats (Beltsville). Within the limits of the experimental design, the data from the three population groups indicated that a more comprehensive study might establish a relation between diet and intravascular disease in humans.

The pathogenetic significance of intravascular coagulation in experimental acute renal failure

Serum and urine fibrin(ogen) degradation products (FDP), FDP clearances, and serum urea nitrogen (SUN) concentrations of rats challenged with glycerol-induced myohemoglobinuria were measured serially over a period of 4 days. The results obtained in animals that developed acute renal failure (ARF) were compared with those obtained in rats made refractory to renal failure by long-term salt loading or recent recovery from prior renal failure. Only the rats susceptible to ARF experienced a major rise in serum FDP concentration. Urine FDP excretion rose most markedly in the same rats but, being elevated in all groups. showed the utilization of fibrinogen whether serum FDP values increased or not. The results obtained might reflect differences in the degree of intravascular coagulation which are pathogenetically important. It is possible, however, that increased serum FDP concentrations found exclusively in rats with ARF are the results rather than the cause of impaired filtration, and that reduced tubular absorption may at least partly account for the high urinary FDP excretion observed in this model of experimental acute renal failure.

Activation of the kallikrein system in hyperbetalipoproteinemia

In 30 patients with hyperlipoproteinemia (19 type II and 11 type IV), the role of the intrinsic coagulation pathway was evaluated by assays of preK, Kl's, and Hageman factor (factor XII). Analysis of the plasma of type II patients suggested activation of the intrinsic pathway characterized by a 40% decrease in preK (p less than 0.01) and a 50% decrease Kl (p less than 0.01); in contrast, analysis of the plasma of type IV patients showed no activation of the intrinsic pathway. In type II patients C-1INH was present in normal concentrations as measured by immunochemical techniques. The findings of normal levels of C-1INH by immunoassay, in association with altered electrophoretic mobility, are suggestive of formation of a kallikrein-C-1INH complex in vivo.

Adenylate cyclase and phosphodiesterase activity in the platelet release abnormality

11 patients with histories of clinical bleeding were selected as examples of platelet release abnormality. Mean bleeding time was 18 +/- 2.6 min (normal +/- SEM; 6 +/- 0.44); mean platelet adhesiveness was 9.9 +/- 4.3% (normal +/- SEM; 30 +/- 2.2). Clot retraction and platelet factor 3 were normal. Platelet aggregation with adenosine diphosphate (ADP), epinephrine and collagen was decreased, as was 14C-serotonin release. Electron microscopic studies of platelets exposed to epinephrine showed 2 subgroups: one which failed to aggregate or have centralization of organelles and a second which developed pseudopodia and centralization of organelles, but rarely aggregated or degranulated. Measurements of activity of adenylate cyclase and phosphodiesterase under basal conditions were performed on platelets from patients and control subjects. Adenylate cyclase activity was significantly lower and phosphodiesterase activity significantly higher in the patient group. Prostaglandin E1 was a potent stimulator of adenylate cyclase in both groups, as was NaF. It was concluded that the causative defects with "platelt release abnormality" do not reside in either the activity of adenylate cyclase or of phosphodiesterase. Changes in formation and destruction of cyclic adenosinemonophosphate (AMP) may instead be regarded as a compensatory response to a defect in another effector system.

Effect of clofibrate on intravascular coagulation in hyperlipoproteinemia

Intravascular coagulation (IVC) was evaluated in 19 patients with type II and 11 with type IV hyperlipoproteinemia before and after clofibrate therapy by measurements of soluble fibrin complexes (SFC) in plasma; fibrinolysis was estimated by quantitation of fibrin (ogen) degradation products in serum. Untreated type II and type IV patients had increased SFC (P less than 0.01). The former also had activation of the intrinsic coagulation pathway as evidenced by decreased plasma prekallikrein (P less than 0.001), kallikrein inhibitors (P less than 0.001), and factor XII (P less than 0.02). Although clofibrate treatment of the type II patients did not change plasma lipids, it decreased intravascular coagulation, apparently via decreased factor XII activation and stimulation of fibrinolysis. In contrast, treated type IV patients had unchanged SFC and FDP levels, despite decreased plasma triglycerides (P less than 0.01). Clofibrate-induced changes in blood coagulation are independent of lipid-lowering. Clofibrate therapy decreases intravascular coagulation in type II patients and may help to prevent thromboembolic sequelae.

Amniotic fluid fibrinogen degradation products in the prenatal diagnosis of neural tube defects

Elevated levels of fibrin(ogen) degradation products (FDP) have been detected in second-trimester amniotic fluid in association with open neural tube defects (NTD'S) in the fetus. The FDP assay has been proposed for the prenatal diagnosis of NTD's and in this paper is compared with the established use of the alpha-fetoprotein (AFP) assay. FDP and AFP levels were measured in 132 amniotic fluid samples, including 20 NTD cases. The false negative and false positive rates for the FDP assay are high compared with the AFP assay, but it may be of value as an adjunct assay to reduce the over-all false positive rate.

Coagulation abnormalities in women taking oral contraceptives

Thirteen asymptomatic women taking oral contraceptives (OCs) were compared with normal subjects. Platelet aggregation and serotonin (tagged with carbon 14) release with adenosine diphosphate, epinephrine, and collagen did not differ from controls. Activation of the intrinsic coagulation pathway was evaluated by measurements of factor XII, prekallikrein, and kallikrein inhibitors. Women taking OCs had normal factor XII levels, moderately elevated prekallikrein levels, and decreased kallikrein inhibitor levels, a pattern not consistent with activation of the intrinsic pathway. The concentration of heavy molecular weight fibrinogen derivatives (HMWFD) was significantly elevated (P less than .001). In contrast, fibrin and fibrinogen degradation products in serum were lower than normal (P less than .05). The increased HMWFD concentration may reflect activation of the coagulation system not mediated by factor XII activation nor potentiated by decreased antithrombin III. Thus, plasma coagulation abnormalities rather than platelet changes may be the factor that predisposes women taking OCs to thromboembolic disorders.

Plasma heparin neutralizing activity. Its use in the evaluation of thrombocytopenia and thrombocytosis

Platelets contain heparin neutralizing activity, which is released into plasma following aggregation. This material is probably identical to platelet factor 4. We describe a technic to measure heparin neutralizing activity in platelet-poor plasma based on the serial heparin dilution technic of Harada and Zucker. Heparin neutralizing activity was depressed in thrombocytopenia due to immune thrombocytopenia and bone marrow depression, and elevated in thrombocytopenia due to disseminated intravascular coagulation. Secondary thrombocytosis is characterized by markedly elevated heparin neutralizing activity, while thrombocytosis associated with myeloproliferative disorders has normal heparin neutralizing activity.

Platelet hypersensitivity and intravascular coagulation in paroxysmal nocturnal hemoglobinuria

The patient described had paroxysmal nocturnal hemoglobinuria associated with recurrent arterial as well as venous thrombosis. Study of platelet function revealed hypersensitivity to epinephrine, adenosine 5'phosphate (ADP) and collagen as judged by their ability to aggregate platelets as well as to release 14C serotonin. The release of total nucleotides was also markedly increased over normal with all aggregating agents. The abnormality was localized to the platelet since aggregation occurred when the patient's platelets were resuspended in normal plasma but not when normal platelets were incubated in the patient's plasma. Presumptive evidence for ongoing intravascular coagulation was an increase in fibrinogen derivatives of heavier molecular weight than the native protein presumably a result of thrombin action. However, factor XII was not activated and fibrinolysis was not increased. Complement component levels and antithrombin concentrations were also normal. The findings in this case suggest that hypersensitive platelets may contribute to the intravascular coagulation that is manifested by the increased incidence of thrombosis in patients with paroxysmal nocturnal hemoglobinuria.

Clofibrate reversal of platelet hypersensitivity in hyperbetalipoproteinemia

Platelet function was evaluated in 29 patients with familial hyperbetalipoproteinemia; 17 were untreated and 12 were receiving clofibrate (Atromid-S). In comparison with 26 normal subjects, the untreated patients aggregated in response to 1/3 the concentration of adenosine diphosphate (ADP), 1/25 the concentration of epinephrine, and 1/4 the concentration of collagen. Treatment with clofibrate, 2 g daily, returned the ADP sensitivity of the platelets to normal and returned epinephrine and collagen sensitivity towards normal, even though it did not alter total cholesterol, low-density-lipoprotein (LDL) cholesterol, or triglyceride concentrations significantly.

Platelet nucleotide release was also 3-to-5 fold increased in untreated type II patients. Clofibrate treatment failed to diminish the elevated platelet nucleotide release.

Incubation of clofibrate at therapeutic concentrations (100-200 µu/ml) with normal platelets in vitro decreased their sensitivity to ADP and epinephrine and reduced 14 C-serotonin release by these agents. The effect on the release was probably mediated through decreased platelet sensitivity since higher doses of epinephrine could reverse the inhibitory effect of clofibrate.

Clofibrate may decrease the incidence of thrombotic complications of atherosclerosis by altering platelet sensitivity to aggregation.