Maintenance of platelet viability after platelet-labeling with fluorescein isothiocyanate

Possible effects of an ex vivo fluorescent labeling procedure of blood platelets on the platelet viability were examined by different function tests. The degree of the impairment of the platelet function proved to be principally correlated with the dye concentration used during the labeling procedure. However, the physiological properties of the labeled platelets obviously remain unrestricted by using intraplatelet fluorescein isothiocyanate (FITC) concentrations below 0.55 mg/10(11) platelets, corresponding to 8.5 X 10(6) FITC molecules bound to one platelet. A procedure for fluorescent labeling of blood platelets is described which is considered to be preferably suitable to prepare platelets for vital microscopic platelet observations.

A platelet derived inhibitor of plasma prekallikrein activation

Platelet products released by ADP mediated platelet aggregation or by repeated freeze-thawing of platelet-rich-plasma caused inhibition of the dextran sulphate induced activation of prekallikrein, measured amidolytically, in subsequently prepared platelet-poor-plasma. Platelet products did not inhibit the amidolytic activity of contact activated-plasma. Addition of antiserum to platelet factor-4 (PF4) neutralized the inhibitory effect of platelet products towards prekallikrein activation. When platelet released products were fractionated by heparin affinity chromatography, 93% of the PF4 applied and 86% of the inhibitory activity of the starting material was recovered in the high-affinity fraction.

Platelets and diabetic vascular disease

Tests of platelet behaviour in vitro, particularly aggregation and retention and in vivo tests such as measurement of platelet survival and plasma levels of beta-thromboglobulin are frequently abnormal in diabetic patients, particularly in those with vascular disease. The concept has therefore arisen that platelet hyper-reactivity is one factor responsible for diabetic microangiopathy. Whereas there is experimental and histological evidence for the mediation of platelets in the pathogenesis of atherosclerosis, direct evidence of platelet involvement in microangiopathy is scanty. Similar alterations in platelet behaviour have been observed in a variety of other conditions with vessel wall damage in common and evidence is presented which suggests that these platelet abnormalities may be secondary to vessel wall injury. In diabetic subjects, some changes in platelet behaviour are reversed by improved glycaemic control. Evidence that platelets are involved in the pathogenesis of diabetic microangiopathy therefore remains circumstantial, though current trials of anti-platelet agents may enable a more precise evaluation of their role.

Stimulation of histamine release from human basophils by human platelet factor 4

Human basophils were stimulated to release histamine noncytotoxically by purified human platelet factor 4 (PF4) and the synthetic substituent peptide PF4(59-70). Histamine release was augmented significantly by 10(-7) M PF4 and 10(-5) M PF4(59-70), increased in a concentration-dependent manner, and attained a maximum at 3 X 10(-5) M PF4 and 3 X 10(-4) M PF4(59-70) similar to that achieved by goat anti-human myeloma IgE. PF4 (1-60) failed to initiate the release of histamine, which confirmed that the critical determinant of activity is in the carboxy-terminal sequence. Histamine release from basophils by optimally effective concentrations of PF4 and PF4(59-70) reached a plateau by 1-3 min, as contrasted with 10 min or longer for anti-IgE. The elimination of calcium and magnesium from the buffer suppressed the release of histamine by anti-IgE by 79-83%, but had no effect on that elicited by PF4(59-70). The rate of uptake of [125I]PF4 by purified basophils was similar on a molar basis to the rate of release of histamine by the same concentrations of PF4. The noncytotoxic release of histamine from human basophils by PF4 thus is temporally and biochemically distinct from that mediated by IgE and may be similar to that evoked by other polycationic stimuli.

Chemotactic activity of platelet alpha granule proteins for fibroblasts

At sites of blood vessel injury, platelets release numerous substances that may have biological activities influencing cellular responses. In this study we examined separately the chemotactic activity for fibroblasts of three highly purified proteins obtained from platelet alpha granules: platelet factor 4 (PF4), platelet-derived growth factor (PDGF), and beta-thromboglobulin (BTG). We observed that each of these proteins was strongly chemotactic for fibroblasts, with maximum chemotactic activity in each instance comparable to that observed with an optimal concentration of the control chemotactic protein, plasma fibronectin. Each protein was active at very low concentrations. The peak chemotactic activities of PF4, PDGF, and BTG occurred at 200 mg/ml, 30 ng/ml, and 6 ng/ml, respectively. Specificity of fibroblast chemotaxis to individual platelet proteins was provided by finding that anti-PF4 immunoglobulin blocked the chemotactic activity of PF4 without affecting the chemotactic activity of PDGF, while anti-PDGF immunoglobulin blocked the activity of PDGF but did not alter the capacity of PF4 to promote fibroblast chemotaxis. These results suggest that in vivo several alpha granule proteins released from platelets may affect wound healing by causing directed fibroblast migration.

Influence of inhibitor of glucose utilization on the blood platelet function

The inhibition of glycolysis by an inhibitor of glucose utilization isolated from urine of the uremic subjects reflects in: (1) decreased platelet aggregation induced by adenosine diphosphate, adrenaline, or collagen, respectively; (2) decreased platelet factor 4 release induced by the same inductors; (3) decreased availability of platelet factor 3, and (4) inhibition of retraction of reptilase clot. It is concluded that the inhibition of glycolysis by 'inhibitor of glucose utilization' contributes to the functional changes of platelets and thus to the alteration of hemostasis in uremic patients.

Platelet function in coronary artery disease: effects of coronary surgery and sulfinpyrazone

Platelet survival and plasma concentrations of beta thromboglobulin and platelet factor 4 were measured in 44 patients before and 6 months after coronary artery bypass grafting. Postoperatively, patients were randomized to receive sulfinpyrazone, 800 mg/day, or placebo. Preoperatively, platelet survival was significantly shorter than normal, and plasma concentrations of both platelet-specific proteins were significantly elevated. Postoperatively, all three indexes of platelet function tended to become normal, but these changes were statistically significant only in patients treated with sulfinpyrazone. Postoperative exercise testing correlated significantly with plasma concentrations of beta thromboglobulin and platelet factor 4 measured preoperative and postoperative. These results are consistent with reports of the effects of sulfinpyrazine on platelet involvement in other conditions, and suggest that the drug reduces platelet activation and inhibits actual destruction. The results also show a relationship between abnormalities of platelet function and an index of postoperative myocardial ischemia.

In vivo platelet hyperactivity and factor VIII related antigen increase long after myocardial infarction. A controlled effect of sulfinpyrazone

In the Anturane Reinfarction Italian Study the trend of some specific and quantitative haemostatic parameters is being investigated in different series of patients balanced for sulfinpyrazone and placebo. In a series of young male patients who had had myocardial infarction 6 months previously, it has been shown that the placebo treatment subsample presented shortened platelet production time (PPT), increased levels of plasma beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4), and increased factor VIII related antigen (VIII:RAg) compared with a matched control group. A close correlation between plasma concentration of VIII:RAg and PPT was evidenced in the same treatment subsample. The sulfinpyrazone treatment subsample presented normalized PPT accompanied by reduction of VIII:RAg but not of beta-TG or PF4 levels.

The heparin neutralizing activity of venous and polyester aortic grafts

The distribution and variations of heparin neutralizing substances in venous and polyester grafts in the abdominal aorta of dogs were investigated and the results compared with those of normal arteries and veins. 1, 4 and 36 months after the operation the venous and polyester grafts were excised and dissected into three layers. The antiheparin activity of the different layers was then determined. In the early post-operative period, the antiheparin activity in the venous and polyester grafts is higher but later begins to fall so that its level 3 years after the operation approaches that of the various layers in the normal veins.

[Clinical applications of beta-thromboglobulin and platelet factor 4 radioimmune assays (author's transl)]

beta-Thromboglobulin (beta-TG) and the anti-heparin activity platelet factor 4 (PF4) were simultaneously assayed by a radioimmune method in 108 subjects, most of whom had already be studied for platelet kinetics. The following data were obtained : while there was no technical cross-reaction, the two assays correlated closely, which indicates that they explore the same physiological phenomena : when controls were chosen at random in a population of wide age range, considerable differences were observed in the results, the values that could be considered excessive in a large percentage of cases, particularly among old, "normal" individuals ; there was no correlation between beta-TG and PF4 values on the one hand platelet destruction rate on the other ; plasma levels of beta-TG and PF4 were significantly higher in patients with vascular diseases and polycythaemia vera than in control but clearly overlapped with the values observed in controls of the same age group. The clinical significance of these data requires, to be assessed, a long-term prospective study aimed at determining whether patients with high beta-TG and PF4 levels present a high risk of thromboembolic complications and whether this risk can be reduced by correcting the biological abnormality with agents altering platelet function.

Vascular permeation of platelet factor 4 after endothelial injury

Antibody to platelet factor 4 was used to demonstrate permeation of this factor into the blood vessel wall after endothelial injury in rabbits. The presence of platelet factor 4 antigen in the vessel wall after removal of the endothelium was shown by immunofluorescence 10 and 30 minutes after injury but not 240 minutes afterward. This study demonstrates that factors carried by platelets can enter the vessel wall and that the movement of these platelet products into the vasculature is a short-lived, self-limiting process.

Platelet factor 4 regulates osteoclastic bone resorption in vitro

Platelet factor 4, which inhibits collagenases derived from both human skin and granulocytic extracts, was found to block reversibly parathyroid hormone-stimulated 45Ca release from fetal rat bone in vitro. The inhibitory property was equally effective in both actively resorbing bones and in bones stimulated to initiate resorption.

Relationship between secretion of platelet Factor 4 and thrombin generation during in vitro blood clotting

We have studied the effects of both impaired prothrombin activation and direct inhibition of thrombin on the platelet release reaction in clotting blood to determine the role of thrombin in this process. In blood from two patients with congenital Factor V deficiency, prothrombin activation during spontaneous in vitro clotting was delayed and decreased. Secretion of platelet Factor 4 was also delayed and was detected only after thrombin formation was initiated. Addition of a small amount of normal plasma to the patients' blood in vitro corrected the abnormalities in both thrombin formation and the platelet release reaction in parallel fashion. A delay in the onset of secretion of platelet Factor 4 was also observed when thrombin generated in normal blood during spontaneous in vitro clotting was inhibited by either purified hirudin or anti-thrombin Fab. These observations suggest that thrombin is the essential stimulus for platelet secretion during in vitro blood clotting. The effect of inhibitors of the platelet release reaction on prothrombin activation during in vitro blood clotting was also studied. When either prostacyclin or the combination of prostaglandin E(1) and N(6)O(2')-dibutyryl cyclic AMP was added, secretion of platelet Factor 4 was inhibited 85-95%. We were unable to detect any inhibition of initiation of prothrombin activation or inhibition of that part of thrombin generation associated with clotting. These results indicate either that the platelet release reaction may not be required for the initiation of prothrombin activation or only a very limited amount of secretion may be necessary for normal generation of thrombin to occur.

Influence of mithramycin on some platelet functions in vitro

Platelet-rich plasma was incubated with mithramycin in vitro. This diminished platelet aggregation by ADP and adrenaline, but did not interfere with collagen-induced aggregation. Platelet factor 4 release was diminished by ADP and delayed when induced by adrenaline but normal when induced by collagen. Platelet factor 3 availability was not significantly impaired. Reptilase clot retraction was diminished when induced by ADP but normal when induced by collagen. Uptake of 14C-serotonin and 14C-adenine was slightly inhibited. There was no depression in platelet adhesion or release of serum aggregating activity.