Hepatic Platelet Research Articles

Platelet adhesion and fibrinogen deposition in murine microvessels upon inhalation of nanosized carbon particles.

The translocation of nanoparticles in the lung toward effector organs via the circulation is considered an important direct pathway for systemic effects of nanoparticles after inhalation. Recently, we have reported that a moderate dose of systemically administered nanosized carbon black particles exerted thrombogenic effects in hepatic microvessels of healthy mice. This study addresses the questions of whether similar thrombogenic effects are also evoked upon inhalation of nanosized carbon particles (NCP) and whether NCP-induced hepatic platelet accumulation is associated with pulmonary or systemic inflammation. Two and 8 h after a 24-h exposure to either filtered air or to NCP, intravital fluorescence microscopy of the hepatic microcirculation was performed in C57Bl/6 mice. Parameters of pulmonary or systemic inflammatory response were determined in bronchoalveolar lavage and blood/plasma samples. Inhalative exposure to NCP caused platelet accumulation in the hepatic microvasculature, whereas leukocyte recruitment and sinusoidal perfusion did not differ from controls. Fibrinogen deposition was detected by immunohistochemistry in both hepatic and cardiac microvessels from NCP-exposed mice. In contrast, inhalation of NCP affected neither the plasma levels of proinflammatory cytokines nor blood cell counts. Moreover, the bronchoalveolar lavage data indicate that no significant inflammatory response occurred in the lung. Thus, exposure to NCP exerts thrombogenic effects in the microcirculation of healthy mice independent of the route of administration (i.e. inhalation or systemic intra-arterial administration). The NCP-induced thrombogenic effects are not liver specific, are associated with neither a local nor a systemic inflammatory response, and seem to be independent of pulmonary inflammation.

Hepatic platelet accumulation in Fas-mediated hepatitis in mice

Platelets are reported to be causally involved in experimental hepatitis. Jo2, an agonistic anti-Fas antibody, induces hepatitis in mice. We examined the in vivo behaviors of platelets in mice injected with this antibody (analyzed by measuring 5-hydroxytryptamine, a constituent of platelets). We found that Jo2 induces platelet accumulation predominantly in the liver, and that this hepatic platelet accumulation (HPA) precedes the increases in hepatitis markers (alanine- and asparagine-aminotransferases [ALT and AST]). By electron microscopy, we detected entry of platelets into hepatocytes, and also evidence of apoptosis among hepatocytes. A caspases-3/6/7/8/10 inhibitor prevented the Jo2-induced HPA and hepatitis. In platelet-depleted mice, contrary to our expectations, the Jo2-induced hepatitis was not reduced, and actually the increase in AST was significantly augmented, although the survival time of mice given a lethal dose of Jo2 was significantly increased (nearly doubled). Interestingly, prior induction of HPA by a low dose of lipopolysaccharide markedly reduced Jo2-induced hepatitis. Jo2 also induced HPA and hepatitis in mice deficient in both IL-1 and TNFα, although Jo2 increased the blood level of TNFα in wild-type mice. These results suggest that in Jo2-induced hepatitis: (i) platelets accumulate predominantly in the liver as a result of hepatic lesions, and that this precedes the release of transaminases from hepatocytes, and (ii) IL-1 and TNFα are not essential for Jo2-hepatitis. We hypothesize that platelet accumulation in the liver may, contrary to our expectations, be protective when the hepatitis is local or not severe, but harmful when hepatitis is severe.

Platelet‐dependent accumulation of leukocytes in sinusoids mediates hepatocellular damage in bile duct ligation‐induced cholestasis

Although it is well known that extrahepatic cholestasis induces liver damage, the mechanisms are still not completely understood. The aim of the present study was to evaluate the role of platelets and P-selectin in cholestasis-induced liver injury. C57BL/6 mice underwent bile duct ligation (BDL) and pretreatment with an anti-GP1balpha antibody, which depletes platelets, an anti-P-selectin antibody or a control antibody. Hepatic platelet and leukocyte recruitment as well as microvascular perfusion were determined by intravital fluorescence microscopy. BDL caused significant liver damage and sinusoidal perfusion failure. BDL further induced hepatic platelet accumulation with widespread intravascular platelet aggregates, increased platelet adhesion in postsinusoidal venules and massive platelet accumulation in liver sinusoids. Administration of the anti-GP1balpha antibody reduced systemic platelet count by 90%. Depletion of platelets in BDL mice not only abolished accumulation and adhesion of platelets in sinusoids and venules but also restored sinusoidal perfusion and reduced liver enzymes by more than 83%. Platelet depletion further reduced BDL-associated sinusoidal leukocyte accumulation by 48% although leukocyte-endothelium interactions in venules were not affected. Immunoneutralization of P-selectin also inhibited hepatic microvascular accumulation of platelets and leukocytes, and protected against cholestasis-provoked hepatocellular damage. Platelets play an important role in BDL-induced liver injury by promoting leukocyte recruitment and deteriorating microvascular perfusion. Moreover, our findings demonstrate that cholestasis-induced accumulation of platelets is mediated by P-selectin. Thus, targeting platelet accumulation may be a useful strategy against liver damage associated with obstructive jaundice.

EORTC Study 26041–22041: Phase I/II study on concomitant and adjuvant temozolomide (TMZ) and radiotherapy (RT) with or without PTK787/ZK222584 (PTK/ZK) in newly diagnosed glioblastoma—Results of a phase I trial

2026 Background: VEGF is an essential mediator of angiogenesis. PTK/ZK is an orally available tyrosine kinase inhibitor of all known VEGF receptors. The EORTC has initiated a randomized phase I/II study in which PTK/ZK is being investigated in combination with standard RT and concomitant TMZ. The results of the safety and dose-finding run-in of the triple combination are reported here. Methods: Escalating doses of PTK/ZK QD continuously (using classical 3+3 design) and concomitant RT (60 Gy) and TMZ (75 mg/m2/day) during 6–7 weeks were to be administered. During the adjuvant/maintenance part, PTK/ZK was prescribed at a fixed standard dose of 750mg bid until progression. Dose limiting toxicities (DLT) were defined as >G3 toxicity occurring during RT + 2 weeks. Results: 18 GBM pts (M/F: 11/7, median age: 53 years, PS 0/1) have been enrolled and complete data for 15 pts are currently available. DL1 (500 mg): 4 pts; no DLT; DL2 (1000 mg): 6 pts: 1 DLT: G3, liver enzyme (ALAT) elevation and hyponatremia DL3 (1250 mg); 8 pts: 3 DLTs: G3 hepatic toxicity (2 pts) and G3 platelets and G4 neutrophil (1 pt). In a 4th patient a G3 diarrhea and hepatic DLT leading to PTK/ZK interruption was doubtful therefore it was decided to extend DL3. Frequently observed possibly related non-dose limiting drug adverse events of all grades included: abdominal pain/cramping (2 pts), ALAT/ASAT elevation (10 pts), creatinine elevation (2 pts), allergic reaction (2 pts), constipation (4 pts), diarrhea (5 pts), fatigue (11 pts), hypertension (6 pts), nausea (8 pts), vomiting (3 pts), and weight loss (4 pts). All toxicities were reversible. Conclusions: MTD has been reached at 1250 mg and the recommended dose of PTK/ZK in combination with RT and TMZ is 1000 mg/day. A randomized 3-arm phase II will start accrual in January 2007. Patients will receive standard TMZ/RT alone or with PTK/ZK starting at the beginning of radiotherapy or at the beginning of adjuvant therapy 4 weeks after the end of radiotherapy. [Table: see text]

Involvement of Kupffer cells in lipopolysaccharide-induced rapid accumulation of platelets in the liver and the ensuing anaphylaxis-like shock in mice

Intravenous injection of Klebsiella O3 lipopolysaccharide (LPS) into BALB/c mice induces an anaphylaxis-like shock within minutes. Using 5-hydroxytryptamine as a marker for platelets, we previously suggested that a rapid platelet accumulation in the liver and lung precedes the shock, and that a complement-dependent platelet-degradation is involved in the shock. Here, we examined (i) the effect of platelet-depletion (using an anti-platelet monoclonal antibody) on the shock and (ii) the contribution of macrophages to the platelet-accumulation in those organs. LPS-induced platelet-accumulations in the liver and lung were confirmed by immunostaining. In platelet-depleted mice, the shock was largely prevented. The number of F4/80-positive macrophages was much greater in liver than in lung, and the hepatic macrophages were largely lost in mice given clodronate-encapsulated liposomes. In mice treated with such liposomes, both the LPS-induced accumulation of platelets in the liver (but not in the lung) and the shock were largely prevented, and repopulation of hepatic macrophages restored these LPS-induced responses. These results suggest that (i) platelets are indeed involved in the shock, (ii) Kupffer cells mediate the hepatic platelet accumulation, and (iii) preventing this hepatic accumulation can largely prevent rapid shock being induced by LPS (at the dose used here).

Hepatic platelet and leukocyte adherence during endotoxemia

IntroductionLiver microcirculation disturbances are a cause of hepatic failure in sepsis. Increased leukocyte-endothelial interaction, platelet adherence and impaired microperfusion cause hepatocellular damage. The time course and reciprocal influences of ongoing microcirculatory events during endotoxemia have not been clarified.MethodsMale Wistar rats (232 ± 17 g) underwent cecal ligation and puncture (CLP). Intravital microscopy (IVM) was performed 0, 1, 3, 5, 10 and 20 hours after CLP. Mean erythrocyte velocity, leukocyte and platelet rolling in postsinusoidal venules and sticking of leukocytes and platelets in postsinusoidal venules and hepatic sinusoids were determined. Heart rate (HR), mean arterial pressure (MAP) and portal venous blood flow (PBF) were measured. Blood count and investigation of hepatic enzyme release was performed after each IVM time point.ResultsHepatic platelet-endothelial adherence in liver sinusoids and postsinusoidal venules occurred one hour after the induction of endotoxemia. Leukocyte-endothelial interaction started three to five hours after CLP. A decrease of hepatic microperfusion could be observed at three hours in sinusoids and ten hours in postsinusoidal venules after CLP, although PBF was reduced one hour after CLP. HR remained stable and MAP decreased ten hours after CLP. Hepatic enzymes in blood were significantly elevated ten hours after CLP.ConclusionHepatic platelet-endothelial interaction is an early event during endotoxemia. Leukocyte adherence occurs later, which underlines the probable involvement of platelets in leukocyte recruitment. Although PBF is reduced immediately after CLP, the later onset of hepatic microperfusion decrease makes the existence of autoregulatory liver mechanisms likely.

Effect of increased hepatic platelet activating factor and its receptor portal hypertension in CCl4-induced liver cirrhosis

To evaluate the changes in hepatic platelet activating factor (PAF) and its receptors and their effect on portal pressure of cirrhotic rats induced by CCl4. A model of liver cirrhosis was replicated in rats by intra-peritoneal injection of CCl4 for 8 wk. We determined the effect of hepatic PAF and its receptor level on portal and arterial pressure by EIA, saturation binding and RT-PCR technique. Compared to control rats, cirrhotic rats had higher hepatic PAF levels and output as well as higher plasma PAF levels (P<0.01, P<0.01, P<0.05, respectively). Both hepatic PAF receptor mRNA levels and PAF binding were nearly 3-fold greater in cirrhotic rats (P<0.01). Portal injection of PAF (1 g/kg WT) increased the portal pressure by 22% and 33% in control and cirrhotic rats, respectively. In contrast, the arterial pressure was decreased in the both groups (54% in control rats and 42% in cirrhotic rats). Injection of the PAF antagonist BN52021 (5 mg/kg WT) decreased the portal pressure by 16% in cirrhotic rats but had no effect in the control rats. The upregulation of the PAF system contributes to hepatic hemodynamic and metabolic abnormalities in cirrhosis, and the increased release of PAF into the circulation has impacts on the systemic hemodynamics.

Modulation of antioxidant enzyme activities, platelet aggregation and serum prostaglandins in rats fed spray-dried milk containing n-3 fatty acid

Spray-dried milk enriched with n-3 fatty acids from linseed oil or fish oil were fed to rats to study its influence on liver lipid peroxides, hepatic antioxidant enzyme activities, serum prostaglandins and platelet aggregation. Significant level of alpha linolenic acid, eicosapentaenoic acid and docosahexaenoic acid were accumulated at the expense of arachidonic acid in the liver of rats fed n-3 fatty acid enriched formulation. The linseed oil and fish oil enriched formulation fed group had 44 and 112% higher level of lipid peroxides in liver homogenate compared to control rats fed groundnut oil enriched formulation. Catalase activity in liver homogenate was increased by 37 and 183% respectively in linseed oil and fish oil formulation fed rats. The glutathione peroxidase activity decreased to an extent of 25-36% and glutathione transferase activity increased to an extent of 34-39% in rats fed n-3 fatty acids enriched formulation. Feeding n-3 fatty acid enriched formulation significantly elevated the n-3 fatty acids in platelets and increased the lipid peroxide level to an extent of 4.2-4.5 fold compared to control. The serum thromboxane B2 level was decreased by 35 and 42% respectively in linseed oil and fish oil enriched formulation fed rats, whereas, 6-keto- prostaglandin F1alpha level was decreased by 17 and 23% respectively in linseed oil and fish oil enriched formulation fed rats. The extent and rate of platelet aggregation was decreased significantly in n-3 fatty acids enriched formulation fed rats. This indicated that n-3 fatty acids enriched formulation beneficially reduces platelet aggregation and also enhances the activities of hepatic antioxidant enzymes such as catalase and glutathione transferase.

Modulation of antioxidant enzyme activities, platelet aggregation and serum prostaglandins in rats fed spray-dried milk containing n-3 fatty acid

Spray-dried milk enriched with n-3 fatty acids from linseed oil (LSO) or fish oil (FO) were fed to rats to study its influence on liver lipid peroxides, hepatic antioxidant enzyme activities, serum prostaglandins and platelet aggregation. Significant level of alpha linolenic acid, eicosapentaenoic acid and docosahexaenoic acid were accumulated at the expense of arachidonic acid in the liver of rats fed n-3 fatty acid enriched formulation. The linseed oil and fish oil enriched formulation fed group had 44 and 112% higher level of lipid peroxides in liver homogenate compared to control rats fed groundnut oil enriched formulation. Catalase activity in liver homogenate was increased by 37 and 183% respectively in linseed oil and fish oil formulation fed rats. The glutathione peroxidase activity decreased to an extent of 25-36% and glutathione transferase activity increased to an extent of 34-39% in rats fed n-3 fatty acids enriched formulation. Feeding n-3 fatty acid enriched formulation significantly elevated the n-3 fatty acids in platelets and increased the lipid peroxide level to an extent of 4.2 to 4.5-fold compared to control. The serum thromboxane B2 level was decreased by 35 and 42% respectively in linseed oil and fish oil enriched formulation fed rats, whereas 6-keto-prostaglandin F1alpha level was decreased by 17 and 23% respectively in linseed oil and fish oil enriched formulation fed rats. The extent and rate of platelet aggregation was decreased significantly in n-3 fatty acids enriched formulation fed rats. This indicated that n-3 fatty acids enriched formulation beneficially reduces platelet aggregation and also enhances the activities of hepatic antioxidant enzymes such as catalase and glutathione transferase.

Controversial role of nitric oxide in hepatic structural and functional injury

Nitric oxide (NO) may regulate hepatic metabolism directly by causing alterations in hepatocellular (hepatocyte and Kuptfer cell) metabolism and function or indirectly as a result of iU vasodilator properties. NO may be released from the hepatic vascular endothelium, platelets, nerve endings, mast cells, and Kupffer cells as a response to various stimuli such as endotoxemla, ischemia-reperfusion injury, and circulatory shock. It is synthesized by nitric oxide synthase (NOS), which has three distinguishable isofonns: NOS-I (ncNOS), a constitutive isofonn originally isolated from neuronal sources; NOS-2 (iNOS), an inducible isofonn that may generate large quantities of NO and may be Induced In a variety of cell types throughout the body by the action of Inflammatory stimuli; and NOS-3 (ecNOS), a constitutive isofonn originally located in endothelial cells. It is believed that Kupffer cells are the main source of NO during endotoxemic shock and that selective inhibition of this stimulation may have future beneficial therapeutic implications. NO may possess both cytoprotective and cytotoxic properties depending on the amount and the lsofonn of NOS by which It Is produced. The mechanisms by which these properties are regulated are Important In the maintenance of whole body homeostasis and remain to be elucidated.

Nitric oxide in liver transplantation.

Liver transplantation is the only therapeutic option for patients with end-stage liver disease. Nitric oxide, a free radical produced from L-arginine, a potent vasodilator, also inhibits platelet adhesion and aggregation, reduces adhesion of leukocytes to the endothelium and suppresses proliferation of vascular smooth muscle cells. The inducible form of the nitric oxide synthase may generate large quantities of nitric oxide, and may be induced by the action of cytokines and lipopolysaccharides. Nitric oxide can be released from the hepatic vascular endothelium, platelets and Kupffer cells as a response to ischemia-reperfusion injury and circulatory shock. We analyzed the relationships between the levels of nitric oxide, hepatic enzymes and other clinical parameters (glucose, total proteins, total bilirubin, creatinine, albumin) obtained in serum samples before liver transplantation and every 48 h till day 15 in 15 patients aged 40 +/- 13 years. Aspartate aminotransferase and alanine aminotransferase levels changed from high at the beginning, to almost normal at the end of the study, cholinesterase levels remained decreased throughout the study and nitric oxide remained high, never reaching normal values.

Expression of P-Selectin on Hepatic Endothelia and Platelets Promoting Neutrophil Removal by Liver Macrophages

The role of P-selectin on polymorphonuclear leukocyte (PMN) adhesion-induced PMN elimination in the liver is unclear. Our objectives were to show the expression and distribution of P-selectin in rat liver, as well as to evaluate the changes in the modulation of the expression of P-selectin and its role in the accumulation and sequestration of PMNs. The intravenous administration of endotoxin markedly increased the expression of P-selectin on the venous and sinusoidal endothelial cells, as well as on the platelets trapped in the liver. Its expression peaked at 6 hours postinjection and was associated with a rapid increase in the aggregation and elimination of PMNs in the hepatic sinusoids. Combined treatment with an antibody to P-selectin or with low molecular weight heparin, a P-selectin antagonist, blocked the P-selectin, significantly reduced the arrest of PMNs, and delayed their removal in the liver. Pretreatment with gadolinium chloride inhibited phagocytosis of PMNs by the Kupffer cells, decreased the expression of P-selectin, and limited the hepatic accumulation of PMNs. Thus, P-selectin played a role in accumulation and elimination of PMNs from the liver. Results also suggest that activated Kupffer cells can modulate the expression of P-selectin in the liver and influence the homeostasis of PMNs in the circulation during acute inflammation.

Gadolinium chloride treatment attenuates hepatic platelet accumulation after lipopolysaccharide administration.

Intravenous administration of LPS to rats results in the accumulation of both neutrophils and platelets in the liver and the development of midzonal hepatocellular necrosis. The development of liver injury entails contributions from both cellular and soluble mediators, including neutrophils, platelets, Kupffer cells, tumor necrosis factor-alpha (TNF-alpha), and components of the coagulation system. Much remains unknown about the interactions among these mediators in the pathogenesis of liver injury in vivo. Accordingly, we conducted studies with gadolinium chloride (GdCl3), an agent that inhibits Kupffer cell phagocytosis, to evaluate the role of Kupffer cells in lipopolysaccharide (LPS)-mediated liver injury, elevation in plasma TNF-alpha activity, thrombocytopenia, hepatic platelet accumulation, and activation of the coagulation system. Female Sprague-Dawley rats were pretreated with GdCl3-6H2O (10 mg/kg, i.v.) or saline vehicle 24 h before the administration of LPS (4 mg/kg, i.v.) or saline vehicle. In a preliminary study, this GdCl3 treatment regimen decreased the clearance of colloidal carbon from blood, indicating inhibition of Kupffer cell phagocytosis. Pretreatment with GdCl3 attenuated LPS-induced liver injury, monitored as increased plasma alanine aminotransferase and isocitrate dehydrogenase activities and histologic analysis. Electron micrographs of livers from rats treated with LPS revealed platelets within the sinusoids as well as Kupffer cells with phagolysosomes containing material resembling platelets. Pretreatment with GdCl3 attenuated LPS-induced thrombocytopenia and hepatic platelet accumulation, as measured by radiolabeled platelets. Treatment with GdCl3 did not, however, alter the elevation in plasma TNF-alpha activity or the activation of the coagulation system, as evidenced by a decreased in plasma fibrinogen concentration. These results suggest that Kupffer cells contribute to LPS-induced hepatic platelet accumulation and raise the possibility that protection against LPS-induced hepatic injury by Kupffer cell inactivation may be due at least partly to decreased deposition of platelets within the liver.

The role of low molecular weight dextran on platelet pulmonary trapping during endotoxin-induced shock

In vivo behaviour of Indium-111-labelled platelets were followed simultaneously in the lungs, liver, spleen and kidneys in 16 adult sheep which were exposed to intravenous injection of endotoxin (10 micrograms/kg body wt.). The effects on the respiratory function and the central hemodynamics were also followed. Eight sheep received, 30 min after the endotoxin challenge, continuous intravenous infusion of low molecular weight dextran during 4 h while the other eight animals served as controls. A marked pulmonary and hepatic platelet sequestration was observed during and just after the endotoxin infusion and was followed by a marked platelet disaggregation within 30 min in both the groups. Three hours after the endotoxin a second wave of platelet sequestration occurred in the control animals, both in the lungs and in the liver, but no such increase was seen in the low molecular weight dextran-treated group. Within the kidneys only minor changes occurred during the experiment period. In the spleen, however, there was a decrease in platelet sequestration after endotoxin in both groups. Less marked hemodynamic and respiratory alterations occurred in the dextran-treated group compared to the controls. It was concluded that low molecular weight dextran decreases sequestration of platelets in the lungs and in the liver of sheep during endotoxic shock.

Platelet Turnover and Kinetics in Immune Thrombocytopenic Purpura: Results With Autologous 111In-Labeled Platelets and Homologous 51Cr-Labeled Platelets Differ

Mean platelet survival and turnover were simultaneously determined with autologous 111In-labeled platelets (111In-AP) and homologous 51Cr-labeled platelets (51Cr-HP) in ten patients with chronic immune thrombocytopenic purpura (ITP). In vivo redistribution of the 111In-AP was quantitated with a scintillation camera and computer-assisted image analysis. The patients were divided into two groups: those with splenic platelet sequestration (spleen-liver 111In activity ratio greater than 1.4), and those with diffuse sequestration in the reticuloendothelial system. The latter patients had more severe ITP reflected by pronounced thrombocytopenia, decreased platelet turnover, and prominent early hepatic platelet sequestration. Mean platelet life span estimated with 51Cr-HP was consistently shorter than that of 111In-AP. Platelet turnover determined with 51Cr-HP was thus over-estimated. The difference in results with the two isotope labels was apparently due to greater in vivo elution of 51Cr. Although the limitations of the techniques should be taken into account, these findings indicate that platelet turnover is not always normal or increased in ITP, but is low in severe disease. We suggest that this may be ascribed to damage to megakaryocytes by antiplatelet antibody. The physical characteristics in 111In clearly make this radionuclide superior to 51Cr for the study of platelet kinetics in ITP.

Platelet turnover and kinetics in immune thrombocytopenic purpura: results with autologous 111In-labeled platelets and homologous 51Cr- labeled platelets differ

Mean platelet survival and turnover were simultaneously determined with autologous 111In-labeled platelets (111In-AP) and homologous 51Cr- labeled platelets (51Cr-HP) in ten patients with chronic immune thrombocytopenic purpura (ITP). In vivo redistribution of the 111In-AP was quantitated with a scintillation camera and computer-assisted image analysis. The patients were divided into two groups: those with splenic platelet sequestration (spleen-liver 111In activity ratio greater than 1.4), and those with diffuse sequestration in the reticuloendothelial system. The latter patients had more severe ITP reflected by pronounced thrombocytopenia, decreased platelet turnover, and prominent early hepatic platelet sequestration. Mean platelet life span estimated with 51Cr-HP was consistently shorter than that of 111In-AP. Platelet turnover determined with 51Cr-HP was thus over-estimated. The difference in results with the two isotope labels was apparently due to greater in vivo elution of 51Cr. Although the limitations of the techniques should be taken into account, these findings indicate that platelet turnover is not always normal or increased in ITP, but is low in severe disease. We suggest that this may be ascribed to damage to megakaryocytes by antiplatelet antibody. The physical characteristics in 111In clearly make this radionuclide superior to 51Cr for the study of platelet kinetics in ITP.

Platelet Sequestration During Hypothermia in Dogs Treated with Sulphinpyrazone and Ticlopidine - Reversibility Accelerated After Intra-Abdominal Rewarming

During body cooling, a progressive thrombocytopenia is observed, with platelet sequestration mainly in the liver. Platelets return progressively to the circulation during rewarming. In this work the presence of platelet clumps is demonstrated by electron microscopy inside the hepatic sinusoids of dogs cooled to 20 degrees C by immersion in iced water. Such clumps were not found either before cooling or after body rewarming. Similar platelet clumps in the hepatic microcirculation were found in two other groups of dogs cooled and rewarmed as before, but previously treated with the antiaggregants sulphinpyrazone or ticlopidine. Another group of dogs was cooled and rewarmed by intra-abdominal circulation of physiological saline respectively at 4 degrees C and 40 degrees C. In these animals a similar decrease of circulating platelets was observed. However, just after rewarming was started, with the body temperature still at 22 degrees C, sequestered platelets came back abruptly to circulation. We conclude that hepatic platelet sequestration induced by hypothermia appears mainly due to local haemodynamic conditions.

Depressed reticuloendothelial clearance of platelets in rats after trauma.

Platelet microembolization may contribute to microcirculatory and organ damage following trauma and shock. It is hypothesized that posttraumatic reticuloendothelial depression predisposes to such microembolization by failure to clear altered platelets from the circulation. The present study evaluated the short-term (1 h) clearance and organ localization of radiolabeled homologous damaged platelets in normal rats and in rats following sublethal Noble-Collip drum trauma. Platelets were collected in citrated platelet-rich plasma from normal rats and labeled with 51Cr in citrated saline. Platelets were altered by repeated centrifugation in protein-free medium. These platelets differed functionally and morphologically from normal platelets. Disappearance of iv injected damaged platelets conformed to a two-compartment exponential clearance. Velocity of clearance in the rapid compartment correlated with hepatic platelet localization, whereas velocity of clearance in the second compartment correlated with splenic platelet localization. Clearance rate of the rapid compartment was depressed at 1 h after trauma and elevated at 24 h. These changes were associated with a decrease in hepatic platelet localization at 1 h and an increase above normal at 24 h. Splenic platelet localization was decreased by 3 h following trauma. Pulmonary platelet localization was increased at all times following trauma. It is concluded that the posttrauma state is associated with a defect in the reticuloendothelial system clearance of altered platelets, which may augment embolization of platelets in the lung.

Platelet removal from the circulation by the liver and spleen.

Previous studies on the clearance of intravenously administered platelets have focused primarily on the long-term survival of platelets rather than the mechanisms responsible for the rapid removal of altered platelets from the blood. In the present study the short-term blood clearance and organ localization of circulating labeled platelets were evaluated in rats during particle induced reticuloendothelial (RE) blockage and after intravenous injection of increasing platelet loads in normal rats. Platelet disappearance conformed to a two-compartment exponential clearance with quantifiable rapid (K1) and slow (K2) rate constants. As platelet load increased, the rapid rate constant decreased. This clearance alteration was associated with a decrease in the percent of the injected platelet load localized in the liver and an increase in lung localization. During RE blockade, a decrease was observed in the clearance rates of both the rapid and slow compartments. Such clearance alterations were associated with decreased hepatic platelet localization and increased pulmonary and splenic platelet localization. Thus, the hepatic reticuloendothelial system may represent a rapid cellular clearance system for altered platelets. When this cellular system is impaired or overloaded, the consequences are decreased hepatic and increased extrahepatic platelet localization.