Survival Of Platelets In Rabbits Research Articles

The relation among vessel injury, thrombus formation, and platelet survival in rabbits

Continuous or repeated injury of rabbit aortae by indwelling vascular catheters caused the deposition of platelets on the injured vessels and the formation of thrombi rich in platelets and fibrin at sites where flow was most disturbed and injury was most extensive. Incorporation of 51Cr platelets into the thrombi reached a maximum between 3 and 24 hr. The platelet-fibrin-rich thrombi remained reactive to circulating platelets for at least 14 days. Continuing reactivity of thrombi and the turnover of platelets in the thrombi were accompanied by an increase in the proportion of platelets that separated in the least dense fraction on Stractan density gradients. Platelet survival was also shortened (43.5 ± 5.9 hr in animals with catheters, compared with 62.6 ± 4.5 hr in animals with a sham operation), indicating that some platelets that had taken part in thrombus formation or had interacted with the injured vessel wall were rapidly cleared from the circulation. Platelets from rabbits that had had indwelling aortic catheters in place for 3 or 6 days survived significantly longer than those from animals with a sham operation upon injection of the platelets into normal animals; thus, continuous turnover of platelets on injured vessels and thrombi, and the clearance of altered platelets, leads to a population of younger platelets that survive longer. The continuing reactivity of thrombi may in part account for repeated occlusive episodes in vascular disease. The contribution of thrombin generation and fibrin formation to the platelet-rich thrombi is substantial and warrants the ongoing evaluation of treatment with a combination of anticoagulant and antiplatelet agents in arterial thrombosis and in thrombus formation on vascular catheters.

The Effect of Dietary Cholesterol on Platelet Survival in the Rabbit – A Study Using 14C-Serotonin and 51Chromium Double-Labelled Platelets

Hypercholesterolemic men and monkeys have shortened platelet survival but attempts to demonstrate this in rabbits have been unsuccessful. The present study examines platelet survival in cholesterol-fed rabbits. Platelets were double-labelled in vitro with 51Cr and 14C-serotonin or in vivo by intravenous injection of 14C-serotonin. In the double-label experiments 51Cr survival was always shorter than 14C survival but changes in survival of one label were accompanied by similar changes in the other label. Survival was shortened after 4 and 7 weeks of cholesterol feeding. This was demonstrated when the donor platelets were from normal rabbits for both cholesterol and control recipients but no shortening was demonstrated when cholesterol-rich platelets were injected into cholesterol-fed recipients and normal platelets were injected into the control rabbits. When 14C-serotonin was injected intravenously 14C survival was the same as when platelets were labelled ex vivo prior to injection and 14C survival was shortened in rabbits fed cholesterol for 1, 2, and 6 weeks. These results indicate that cholesterol-feeding shortens platelet survival. This effect may be masked if the test platelets are not identical in both test and control groups.

Effect of Aspirin and Sodium Salicylate on Thrombosis, Fibrinolysis, Prothrombin Time, and Platelet Survival in Rabbits With Indwelling Aortic Catheters

We have studied the effect of different doses of aspirin on platelet function, PGI2 formation, platelet survival, thrombosis, fibrinolysis, and prothrombin time in rabbits with indwelling aortic catheters. The thrombi formed around indwelling aortic catheters were found to have a large fibrin component, and their formation was inhibited by heparin administration. Thus, in these experiments we examined the effect of aspirin (a weak inhibitor of thrombin-mediated platelet aggregation) under conditions in which thrombin was a major factor in the initiation and growth of the thrombi. Only very high doses of aspirin tended to inhibit thrombus formation over the 5-day period of observation, and a statistically significant inhibition of thrombus formation was produced by equivalent concentrations of sodium salicylate. The failure of high doses of aspirin to achieve a significant inhibition of thrombosis under the conditions of these experiments (whereas an equivalent dose of sodium salicylate was inhibitory) could be due to aspirin inhibition of PGI2 formation. Shortened platelet survival was not affected by aspirin treatment or the dose sodium salicylate that inhibited thrombus formation. The tendency to inhibit thrombus formation appeared to be unrelated to an effect on platelets but was associated with prolongation of the one-stage prothrombin time and increased whole blood fibrinolytic activity; doses of aspirin that inhibited platelet aggregation in response to sodium arachidonate or collagen, and PGI2 formation by the vessel wall, did not have a significant effect on the amount of thrombus present at 5 days. However, the high doses of aspirin that inhibited PGI2 formation were associated with a tendency to increased thrombus formation during the first 3 hr after insertion of the catheter. The results of these experiments show that when thrombin is an important factor in the formation of thrombi, aspirin is a weak inhibitor of thrombosis unless doses are used that provide sufficient salicylate to interfere with blood coagulation and promote whole blood fibrinolytic activity. These results also show that thrombus formation can be inhibited without an apparent change in platelet survival.

Effect of aspirin and sodium salicylate on thrombosis, fibrinolysis, prothrombin time, and platelet survival In rabbits with indwelling aortic catheters

We have studied the effect of different doses of aspirin on platelet function, PGI2 formation, platelet survival, thrombosis, fibrinolysis, and prothrombin time in rabbits with indwelling aortic catheters. The thrombi formed around indwelling aortic catheters were found to have a large fibrin component, and their formation was inhibited by heparin administration. Thus, in these experiments we examined the effect of aspirin (a weak inhibitor of thrombin-mediated platelet aggregation) under conditions in which thrombin was a major factor in the initiation and growth of the thrombi. Only very high doses of aspirin tended to inhibit thrombus formation over the 5-day period of observation, and a statistically significant inhibition of thrombus formation was produced by equivalent concentrations of sodium salicylate. The failure of high doses of aspirin to achieve a significant inhibition of thrombosis under the conditions of these experiments (whereas an equivalent dose of sodium salicylate was inhibitory) could be due to aspirin inhibition of PGI2 formation. Shortened platelet survival was not affected by aspirin treatment or the dose sodium salicylate that inhibited thrombus formation. The tendency to inhibit thrombus formation appeared to be unrelated to an effect on platelets but was associated with prolongation of the one-stage prothrombin time and increased whole blood fibrinolytic activity; doses of aspirin that inhibited platelet aggregation in response to sodium arachidonate or collagen, and PGI2 formation by the vessel wall, did not have a significant effect on the amount of thrombus present at 5 days. However, the high doses of aspirin that inhibited PGI2 formation were associated with a tendency to increased thrombus formation during the first 3 hr after insertion of the catheter. The results of these experiments show that when thrombin is an important factor in the formation of thrombi, aspirin is a weak inhibitor of thrombosis unless doses are used that provide sufficient salicylate to interfere with blood coagulation and promote whole blood fibrinolytic activity. These results also show that thrombus formation can be inhibited without an apparent change in platelet survival.

Reversal of shortened platelet survival in rats by the antifibrinolytic agent, epsilon aminocaproic acid.

Platelet survival in rabbits and rats is shortened by placing indwelling catheters in the aorta; this shortening appears to be at least partly related to the extent of vessel wall injury and platelet interaction with the repeatedly damaged wall. Treatment of rabbit platelets with plasmin and other proteolytic enzymes in vitro shortens their survival when they are returned to the circulation. Because platelets may be exposed to plasmin and other proteolytic enzymes in rabbits and rats with indwelling aortic catheters, we examined the effect of epsilon-aminocaproic acid (EACA) on platelet survival in rats. At a dose of 1 g/kg every 4 h, EACA significantly reduced whole blood fibrinolytic activity and prolonged the shortened platelet survival in rats with indwelling aortic catheters. Mean platelet survival for untreated rats with indwelling aortic catheters was 38.6 +/- 1.9 h, and for rats treated with EACA, 53.8 +/- 3.8 h. Scanning electron microscopy showed that the injured vessel wall of these animals was mainly covered with platelets and fibrin, whereas in control animals that did not receive EACA, the injured surface was mainly covered with platelets and little fibrin was observed. Thus shortened platelet survival during continuous vessel wall injury may result from the local generation of plasmin or the release of proteolytic enzymes at sites where platelets (and possibly leukocytes) interact with the vessel wall.

Platelet survival and thrombosis.

This study examined the relation among platelet survival, thrombosis, and repeated vessel injury. With the use of 51Cr-labeled platelets, indwelling aortic catheters were shown to reduce platelet survival in rabbits and rats. In rabbits, thrombi were observed mainly at the aortic bifurcation and at the tip of the catheter. The amount of thrombus that formed in rabbits with short and long catheters was similar, but platelet survival was shortened only in rabbits with short and long catheters was similar, but platelet survival was shortened only in rabbits with long indwelling aortic catheters. In rats, the aortic catheters did not cause thrombosis, and platelet survival was shortened significantly in rats with both short and long catheters, but was more pronounced in animals with longer catheters. In both rabbits and rats, long aortic catheters caused more extensive vessel injury than the short catheters and this was associated with greater platelet interaction with the vessel wall. Platelet survival cannot be used as an estimate of thrombus formation, but may reflect the extent and frequency of vessel wall injury. thus, shortened platelet survival may represent increased platelet interaction with the damaged arterial wall and increased platelet consumption.

Indium-111 tropolone, a new tracer for platelet labeling.

Platelets have been labeled with a new neutral, lipid-soluble metal complex of indium 111 (111In) and tropolone. Unlike oxine, which is soluble in ethyl alcohol, tropolone is soluble in isotonic saline. Platelet labeling with 111In tropolone can be performed in both acid-citrate-dextrose (ACD) plasma and ACD saline within two hours. Labeling efficiency has been 80% to 90%. 111In tropolone in ACD saline and ACD plasma at tropolone concentrations of 5 and 10 micrograms/ml, respectively, and incubation of the platelets with the tracer at room temperature for 20 minutes were optimal conditions for labeling. The authors have developed an ACD-saline kit for convenient preparation of 111In-labeled platelets. No adverse effect of 111In tropolone on platelets has been observed in studies of biodistribution, recovery, and survival of platelets in rabbits and dogs.

Survival of rabbit platelets treated in vitro with chymotrypsin, plasmin, trypsin, or neuraminidase

Abstract Platelets from which surface sialic acid has been removed by neuraminidase are rapidly cleared from the circulation. In the present study the role of platelet membrane glycoproteins in platelet survival was further investigated with 51Cr-labeled rabbit platelets from which glycoproteins were cleaved by treatment with chymotrypsin, plasmin, or trypsin. SDS-PAGE of platelet membranes followed by PAS staining showed that under the conditions used all of these enzymes cleaved major amounts of glycoprotein I and lesser amounts of glycoproteins II and III. Large percentages of the platelets subjected to any of these proteolytic enzyme treatments or to neuraminidase treatment were removed from the circulation during the hour after their injection (mean values in circulation at 1 hr: control 80.6 %, chymotrypsin-treated 18.3 %, rabbit plasmin-treated 48.4%, pig plasmin-treated 9%, trypsin-treated 2.8%, neuraminidase-treated 4.5%). Some of the platelets treated with chymotrypsin, plasmin, or trypsin were sequestered at 1 hr and had reappeared in the circulation by 4 hr. The platelets were removed by the liver, not by the spleen. Platelet survival was calculated by Murphy's gamma function. Mean platelet survivals (± SEM) for platelets in the circulation at 4 hr were control 77.2 ± 4.2 hr, chymotrypsin-treated 15.9 ± 2.2 hr, plasmin-treated 54.6 ± 6.0 hr. So few of the platelets treated with pig plasmin, trypsin, or neuraminidase remained in the circulation that it was not feasible to calculate platelet survival values. We have shown previously that thrombin treatment of platelets to cause extensive release of granule contents does not alter their survival, in keeping with the finding that it does not affect the major glycoproteins. In the present experiments, plasmin and trypsin caused the platelet release reaction, but chymotrypsin and neuraminidase did not. Thus it appears that loss of granule contents does not influence platelet survival, whereas platelets lacking sialic acid on their membranes (whether it has been removed as sialic acid or as glycopeptides) are recognized as “foreign” and are removed. It may be that the shortened platelet survival seen in thromboembolic complications of arterial disease can at least partly be attributed to the effect of plasmin on platelet glycoproteins, particularly glycoprotein I.

Effect of viruses on platelet aggregation and platelet survival in rabbits

Effect of viruses on platelet aggregation and platelet survival in rabbits

Effect of Viruses on Platelet Aggregation and Platelet Survival in Rabbits

Thrombocytopenia may occur in association with some viral infections. The objective of the present study was to examine the mechanisms by which myxoviruses may induce thrombocytopenia via a direct effect on platelets. Newcastle disease virus (NDV) caused platelet aggregation and loss of granule and cytoplasmic constituents from washed rabbit platelet suspensions. This effect of NDV was abolished by heating the virus at 56°C. In contrast, influenza virus did not cause these platelet reactions. Pretreatment of platelets with NDV abolished their ability to respond to NDV and reduced their response to ADP and thrombin, but treatment of platelets with heated NDV or with influenza virus did not have a major effect on their function in vitro. NDV and influenza virus, which contain neuraminidase activity, removed platelet sialic acid. When platelets pretreated with these viruses were injected into normal rabbits, they were rapidly removed from the circulation. Since platelets pretreated with purified neuraminidase are also rapidly cleared after injection, it seems likely that the loss of platelet sialic acid caused by these viruses is responsible for the removal of the platelets from the circulation. In contrast, platelets treated with inactivated NDV, inactivated influenza virus, or chikungunya virus (which does not have neuraminidase activity) survived normally. Thus there may be at least two mechanisms directly involved in virus-induced thrombocytopenia: (1) paramyxoviruses such as NDV may cause intravascular platelet aggregation, and (2) platelets exposed to viruses with neuraminidase activity may lose surface sialic acid and be rapidly cleared from the circulation.

Platelet survival in rabbits to detect hyperacute rejection

The in vivo platelet survival test, which is based on the rate of disappearance of labelled donor platelets from the circulation of the recipient, was evaluated as a means of assessing preimmunization to transplantation antigens. Platelet survival was shown to correlate closely with the intensity of immunization and proved to be most useful in predicting hyperacute rejection. The immunizing effect of test platelets was variable but slight and could be successfully prevented by 6-MP. The test appears to be more sensitive and accurate in predicting preimmunization than the lymphocyte cytotoxicity test.