Modulatory effect of eugenol on arginase, nucleotidase, and adenosine deaminase activities of platelets in a carrageenan-induced arthritis rat model: A possible anti-arthritic mechanism of eugenol.

This study investigated the effect of eugenol on arginase, nucleotidase and adenosine deaminase activities in platelets of carrageenan-induced arthritic rat model to explain a possible anti-arthritic mechanism of eugenol. Fifty adult female rats (140-250 g) were divided into ten (10) groups (n = 5). Group I received oral administration of corn oil, group II received 2.50 mg/kg of eugenol, group III and IV rats received oral administration of 5.0 and 10.0 mg/kg of eugenol respectively, group V received 0.20 mg/kg of dexamethasone orally, group VI rats was injected with 1% carrageenan (arthritic rats) and received saline solution orally (arthritic control rat group), group VII, VIII and IX: arthritic rats received 2.50, 5.0 or 10 mg/kg of eugenol orally respectively, group X: arthritic rats was administered with 0.20 mg/kg of dexamethasone orally. The animals were treated for 21 days, thereafter, tibiofemoral histological examination, thiobabituric acid reactive substances level, arginase, nucleoside triphosphate diphosphohydrolase, 5´-nucleotidase and adenosine deaminase activities were assessed. Tibiofemoral histological examination result showed that infiltration of inflammatory cells was significantly decreased with an increase in eugenol dose. Activities of arginase, adenosine triphosphate and adenosine monophosphate hydrolyses were significantly decreased while adenosine diphosphate hydrolysis and adenosine deaminase activities were significantly increased in arthritic rat groups administered with different doses of eugenol. Therefore, eugenol might be a natural complement and alternative promising anti-arthritic agent. These possible anti-arthritic mechanisms may be partly through the modulation of arginase and adenosine nucleotides hydrolyzing enzyme activities as well as the antioxidative action of eugenol.

Effect of physical training on indices of platelet aggregation and fibrinogen concentration in patients with chronic heart failure.

OBJECTIVE: The aim of this study was to determine the effect of long-term physical load on the changes in the fibrinogen concentration and platelet aggregation. MATERIAL AND METHODS: Platelet aggregation was investigated in 144 patients while fibrinogen concentration in 138 patients with CHF. The patients were divided into the groups of the trained patients and the controls and were investigated as follows: on admission to the hospital (stage 1); after treatment in the hospital (stage 2); after 3 months (stage 3); after 6 months (stage 4); and after 1 year (stage 5). The indices were investigated before and after physical load. RESULTS: It was determined that fibrinogen concentration significantly increased after physical load in all the treatment stages in both groups of the patients (P=0.045). In the course of the treatment, fibrinogen concentration gradually decreased in the group of the trained patients (P=0.02). Platelet aggregation investigated with ADP significantly increased after physical load in all the stages in both groups of the patients and decreased during the different investigation stages in the groups of the untrained (P=0.02) and trained patients. Platelet aggregation investigated with ADR consistently decreased before physical load during the different investigation stages in the groups of the trained (difference is not significant) and untrained patients (P=0.02). CONCLUSIONS: Physical training reduces fibrinogen concentration in patients with CHF. It remains unclear whether physical training can have an effect on the decrease in platelet aggregation in patients who have long-term physical training applied.

Periodontal disease and high doses of inhaled corticosteroids alter NTPDase activity in the blood serum of rats.

BACKGROUND: Certain drugs such as glucocorticoids may interfere with the modulation of periodontal disease. In contrast, corticosteroid treatment has been associated with a protective effect with regard to periodontal breakdown, depending on the dose, pathway, and exposure time. Considering the potential relevance of nucleotidases in coordinating the cardiovascular system and inflammation processes, the aim of this study was to investigate the nucleotidase activities in the blood serum of rats with periodontal disease exposed chronically to inhaled corticosteroids. METHODS: Adult male Wistar rats (n=26) were randomly assigned to one of the following four study groups: a control group that received no intervention; a periodontal disease group that received saline solution; a 'low dose' group that received 30 µg of budesonide daily; and a corresponding 'high dose' group that received 100 µg daily over a 15-day time course. The hydrolysis of ATP, ADP, and AMP were analysed in blood serum. RESULTS: Periodontal disease diminished the hydrolysis of ATP and enhanced the hydrolysis of ADP. Repeated administration of either a low or high dose in the periodontal disease model of inhaled corticosteroids reversed the observed increase in ADP hydrolysis, and only the repeated administration of low doses of inhaled corticosteroids was able to reverse the decrease in the hydrolysis of ATP induced by periodontal disease. CONCLUSION: The variables investigated in this study may be involved in the pathophysiology of periodontal disease and may participate in the mechanisms that mediate the development of some of the side effects of inhaled corticosteroids.

Antiplatelet loading improves behavioral outcome in a rabbit model of stroke.

BACKGROUND AND PURPOSE: No approved acute therapy exists for thousands of patients with ischemic stroke who present ineligible for thrombolytics. The purpose of this proof-of-concept study was to evaluate the efficacy of acute antiplatelet loading on stroke outcome in the rabbit small clot embolic model. METHODS: Sixty male New Zealand white rabbits were embolized via small clots into the middle cerebral artery. Two hours later, animals were treated with (1) aspirin (5 mg/kg; n=20); (2) usual dual antiplatelet loading (aspirin 10 mg/kg+clopidogrel 10 mg/kg; n=20); or (3) high-dose dual antiplatelet loading (aspirin 10 mg/kg+clopidogrel 30 mg/kg; n=20). The coprimary outcomes were as follows: (1) platelet inhibition and (2) behavioral outcome as measured by the P50 (milligrams of clot that leads to neurological dysfunction in 50% of animals in a group). RESULTS: There was a significant difference in 3-hour arachidonic acid and ADP (P<0.011); 6-hour collagen and ADP (P<0.01, P<0.01); and 24-hour collagen, arachidonic acid, and ADP (P=0.02, P<0.01, P<0.01) platelet inhibition. The behavioral outcome was significantly better in the usual dual antiplatelet loading versus aspirin group (P=0.02). CONCLUSIONS: This study suggests that usual dual antiplatelet loading is clinically beneficial in a validated model of acute stroke. Study of usual dual antiplatelet loading in acute stroke is warranted to provide treatment to stroke victims ineligible for current therapies.

Time-course changes in ectonucleotidase activities during experimental autoimmune encephalomyelitis.

The aim of the present study was to analyze the activities of extracellular purine metabolizing enzymes, CD39 (apyrase, EC 3.6.1.5) and CD73 (ecto-5' nucleotidase, EC 3.1.3.5) in experimental autoimmune encephalomyelitis (EAE). The levels of ATP, ADP and AMP hydrolysis were analyzed in the blood serum and in the rat spinal cord plasma membrane preparation 8, 15 and 25 days after induction of EAE. The animals were divided in three groups: control (saline), CFA (adjuvant-only) and EAE (CFA and homogenate of spinal cords). Eight days after immunization, ATP, ADP and AMP hydrolysis in the blood serum and spinal cord membrane preparations were unaffected in EAE compared to both, control and CFA group. In the peak of disease, ATP, ADP and AMP hydrolysis in EAE group showed significant decrease in the blood serum and prominent increase in the spinal cord membrane preparation compared to CFA and control group. At the end of illness, as judged by disappearance of clinical manifestation of EAE, ATP, ADP and AMP hydrolysis, although closer to CFA levels, were still significantly different in respect to the CFA group. Modulation of ATP, ADP and AMP hydrolysis suggests that they operate during EAE and might represent the basis of novel therapeutic strategies in immune-mediated diseases, such as MS.

Short-term, moderate dosage Vitamin E supplementation may have no effect on platelet aggregation, coagulation profile, and bleeding time in healthy individuals.

OBJECTIVE: To investigate the in vivo effect of short-term, moderate dosage synthetic dl-alpha-tocopherol acetate supplementation on platelet aggregation, coagulation profile, and simulated bleeding time in healthy individuals. alpha-tocopherol is the most biologically active isomer of Vitamin E, traditionally promoted as an antioxidant and therapeutic agent in cardiovascular disease. In vitro studies have suggested that alpha-tocopherol plays a role in the inhibition of platelet aggregation. However, further investigations into the effect of alpha-tocopherol on bleeding in vivo have not duplicated these findings. MATERIALS AND METHODS: A total of 42 healthy volunteers complied with a 2-week abstinence period from the use of anti-platelet agents followed by determination of baseline platelet aggregation properties and coagulation studies using citrated whole blood. Moderate dosage Vitamin E (800 IU of dl-alpha-tocopherol acetate) was then self-administered for 14 days with reevaluation of platelet aggregation and coagulation profile, and simulated bleeding time after 14 days of Vitamin E supplementation. RESULTS: Forty subjects completed the 4-week study period. All 40 subjects demonstrated normal baseline coagulation studies and all had collagen-stimulated platelet aggregation assessment performed in triplicate. After Vitamin E supplementation, no significant difference was demonstrated in any study parameter. CONCLUSIONS: Dietary supplementation with moderate dosage synthetic dl-alpha-tocopherol acetate did not significantly prolong bleeding or platelet aggregation in vivo. The affect of Vitamin E on platelet aggregation in vitro does not appear to be reproducible in vivo. Therefore, peri-operative discontinuation of Vitamin E may not be necessary.

No effect of taurine on platelet aggregation in men with a predisposition to type 2 diabetes mellitus.

Any diet therapy that potentially could affect platelet function would also influence the initiation of atherosclerotic plaque formation which is an important complication of diabetes mellitus eventually resulting in myocardial infarction and stroke. Blood platelets are rich in taurine, and it has been shown that taurine inhibits platelet aggregation in healthy subjects. The purpose was to examine the effect of taurine supplementation on platelet aggregation in high-risk subjects with a positive family history of T2DM. Twenty healthy men were included in a double-blinded, randomized, crossover study, receiving daily supplementation of 1.5 g taurine or placebo for two 8-week periods. Subjects were overweight and first-degree relatives of T2DM patients. At the end of each treatment, fasting blood samples for assessment of platelet aggregation was drawn. Platelet aggregation was induced by ADP. Plasma taurine concentration was significantly greater after taurine intervention compared to placebo (131.4+/-61.7 vs. 38.9+/-6.7 micromol/l, P<0.0001). There was no difference in the threshold level for complete platelet aggregation induced by ADP in vivo between placebo and taurine intervention (placebo 3.86+/-2.21 vs. taurine 3.86+/-3.25 micromol/l). Supplementation with 1.5 g of taurine for 8 weeks had no effect on platelet aggregation in overweight prediabetic men.

Modulation of adenine nucleotide concentrations in human plasma by erythrocytes and endothelial cells.

The regulation of plasma concentrations of adenine nucleotides is unsettled. We tested the possibility of extracellular adenosine triphosphate (ATP) production from adenosine diphosphate (ADP) at physiological low concentrations by erythrocytes and endothelial cells. Filtered erythrocytes and human umbilical vein endothelial cells (HUVEC) were incubated for 15 to 120 s with ADP (10 microM), supplemented with 3H-ADP (2.85 nM) or 14C-ADP (54.6 nM). Enzymatic conversion of ADP to ATP was detected by recovery of the radioactive label in the ATP fraction. ATP was measured in the supernatant using high performance liquid chromatography (HPLC) separation, scintillation techniques, and luminometry. Using etheno (epsilon)-labeled ADP (10 microM), the extracellular localization of the conversion was further corroborated. Following ADP application in plasma, no radioactivity was detected in the ATP fraction. However, in erythrocyte suspensions, 12.9% and 9.7% of the label were recovered in the ATP fraction after application of 3H- and 14C-ADP, respectively. Between 15 and 120 s after 3H-ADP application, the 3H-ATP fraction was found to be stable at around 10%. For the range of ADP concentrations studied (10-40 microM), no saturation of ATP production was achieved. The extracellular localization of conversion was supported by the recovery of the epsilon -label in the epsilon -ATP fraction. In contrast, on HUVEC a conversion of epsilon -ADP to epsilon -ATP was not observed. In conclusion, on erythrocytes there is rapid enzymatic conversion of extracellular ADP to ATP which may play a significant role in adjusting adenine nucleotide concentrations in human plasma. In endothelial cells, extracellular conversion of ADP to ATP is of quantitatively minor importance, if it contributes at all.

Changes in energy metabolism of calf muscle in patients with intermittent claudication assessed by 31P magnetic resonance spectroscopy: a phase II open study.

Energy status and metabolism in skeletal muscle of nine patients with peripheral arterial disease and suffering from intermittent claudication were evaluated using 31phosphorus magnetic resonance spectroscopy (MRS) before and after treatment for 3 months with propionyl-L-carnitine (PLC; 2 g/day p.o.). Maximum walking distance (MWD) was assessed on a standard treadmill (4 km/h, zero incline). For the group as a whole 31P MRS results did not change significantly with PLC. Although MWD increased by a mean of 36%, this change did not reach significance. However, when these variables were assessed with respect to the change in MWD, there were significant differences between those who increased MWD by > 30% (responders, R; n = 5) and those who did not (nonresponders, NR; n = 4). Compared with pretreatment values, during exercise the decrease in muscle pH in R relative to the decrease in phosphocreatine was less after PLC (p = 0.04). After exercise there was a significant inverse correlation between the changes in recovery half-time (t1/2) for phosphocreatine and in MWD (r = -0.91, p = 0.01). With PLC, Vmax increased in R (p = 0.04), but not in NR. For the patient group as a whole, the changes in Vmax and MWD correlated positively (r = 0.90, p = 0.01). This study helps to identify the changes in muscle metabolism that correlate with changes in exercise performance, and may accompany treatment with PLC.

[Various aspects of the anti-aggregatory action of diltiazem and cordaphene in patients with ischemic heart disease]. / Nekotorye aspekty antiagregantnogo deistviia dilzema i kordafena u bol'nykh ishemicheskoi bolezn'iu serdtsa.

Some aspects of the antiaggregatory action of calcium antagonists were studied in 50 patients with stable angina pectoris. Dilzem (diltiazem) and cordaphene (nifedipine) were tested for their effects on the erythrocytic component of hemostasis, taking into account their capability of suppressing hemolysis, which made ADP, an important thrombocytic activator, enter the blood flow. The two agents significantly reduce the concentration of plasma ADP, free hemoglobin, diminish mechanical erythrocytic resistance, and block platelet aggregation to a varying degree. A relationship was established between the levels of blood nifedipine and the magnitude of rheological effects. With this, the patients with coronary heart disease showed a good antianginal effect.

31P-NMR measurements of ATP, ADP, 2,3-diphosphoglycerate and Mg2+ in human erythrocytes.

Absolute 31P-NMR measurements of ATP, ADP and 2,3-diphosphoglycerate (2,3-DPG) in oxygenated and partly deoxygenated human erythrocytes, compared to measurements by standard assays after acid extraction, show that ATP is only 65% NMR visible, ADP measured by NMR is unexpectedly 400% higher than the enzymatic measurement and 2,3-DPG is fully NMR visible, regardless of the degree of oxygenation. These results show that binding to hemoglobin is unlikely to cause the decreased visibility of ATP in human erythrocytes as deoxyhemoglobin binds the phosphorylated metabolites more tightly than oxyhemoglobin. The high ADP visibility is unexplained. The levels of free Mg2+ [( Mg2+]free) in human erythrocytes are 225 mumol/l at an oxygen saturation of 98.6% and instead of the expected increase, the level decreased to 196 mumol/l at an oxygen saturation of 38.1% based on the separation between the alpha- and beta-ATP peaks. [Mg2+]free in the erythrocytes decreased to 104 mumol/l at a high 2,3-DPG concentration of 25.4 mmol/l red blood cells (RBC) and a normal ATP concentration of 2.05 mmol/l RBC. By increasing the ATP concentration to 3.57 mmol/l RBC, and with a high 2,3-DPG concentration of 24.7 mmol/l RBC, the 31P-NMR measured [Mg2+]free decreased to 61 mumol/l. These results indicate, that the 31P-NMR determined [Mg2+]free in human erythrocytes, based solely on the separation of the alpha- and beta-ATP peaks, does not give a true measure of intracellular free Mg2+ changes with different oxygen saturation levels. Furthermore the measurement is influenced by the concentration of the Mg2+ binding metabolites ATP and 2,3-DPG. Failure to take these factors into account when interpreting 31P-NMR data from human erythrocytes may explain some discrepancies in the literature regarding [Mg2+]free.

Dietary polyenoic fatty acids change the response of cat blood platelets to inductions of aggregation by ADP.

Dietary polyenoic fatty acid influence on platelet aggregation has been difficult to assess in mammalian species, as endogenous polyenoic acid production from plant precursors has clouded the effects of diet. The cat is incapable of such endogenous production, and thus is a good experimental model. Adult and juvenile cats dietarily deficient in post delta-6-denaturation fatty acids (PDFA), were supplemented with different PDFA and the ADP-induced platelet aggregation assessed. At the same time, the effects of oral dosage with aspirin, and the exchange of stimulated and non-stimulated plasma were investigated. Animals deficient in all PDFA showed high levels of aggregation, irrespective of aspirin dosage. Feeding only n-6 or n-3 PDFA induced low levels of aggregation, which was reversed by aspirin dosage. Both n-6 and n-3 dietary PDFA together produced very low levels of aggregation, whether aspirin-dosed or not. Thus, ADP-induced platelet aggregation is dependent on the nature of dietary PDFA, and is partially dependent on the presence or absence of aspirin, at least in cases of PDFA imbalance. Non-ADP-stimulated plasma caused only slight changes in aggregation profiles. However, ADP-stimulated plasma from fully sufficient animals produced marked changes in the aggregation pattern of deficient platelets. This indicated the release of an anti-aggregatory substance by normal platelets, but not those of PDFA deficient animals.

Nucleotides in lymphocytes of human subjects with zinc deficiency.

Cell-mediated immunity in human subjects is affected adversely as a result of zinc deficiency. The mechanism by which a deficiency of zinc may affect lymphocyte proliferation and functions, is not well understood at present. Nucleoside phosphorylase (NPase), a purine catabolic pathway enzyme, is zinc dependent, and a congenital deficiency of this enzyme is known to affect adversely cell-mediated immunity. This effect has been related to an accumulation of toxic nucleotides in lymphocytes as a result of NPase deficiency. Inasmuch as the effect of zinc deficiency on the activity of NPase and the levels of nucleotides in human lymphocytes has not been previously reported, we assayed these parameters in human subjects with zinc deficiency before and after zinc supplementation. A mild deficiency of zinc was diagnosed in those having decreased zinc in two out of three cell lineages (less than 42 micrograms in granulocytes, less than 48 micrograms in lymphocytes, and less than 1.70 microgram in platelets, per 10(10) cells). In comparison with five subjects with sufficient zinc, six subjects with zinc deficiency showed a decrease in the activity of NPase (p = 0.01), an increase in adenosine diphosphate (ADP) level (p = 0.008), a decreased adenosine triphosphate (ATP)-to-ADP ratio (p = 0.0001), and an increase in both guanosine triphosphate (GTP) (p = 0.02) and deoxyadenosine triphosphate (dGTP) (p = 0.04 in the lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of polyunsaturated fatty acid diet on the hemorrheological response to physical exercise in hypoxia.

Several studies have shown that hemorrheological parameters are modified by physical exercise and exposure to altitude hypoxia. These changes result in a decrease in red cell deformability (RCD). Similarly, it has been shown that a daily dietary fish oil supplement increases RCD. The purpose of this study was to evaluate the influence of fish oil diet on RCD after exercise. Fourteen male subjects (19-38 years old) were divided into two groups. The first group ate a "standard diet" rich in saturated lipids; the second group received a daily amount of 6 g of MaxEPA fish oil for 6 weeks. Before the 6 weeks of experimental nutrition, and just after this period, both groups were submitted to two physical exercises of 1 h cycling at 70% of their VO2max. One test was performed at sea level, the other at a simulated altitude of 3000 m in a hypobaric chamber. Blood samples were drawn before and after exercise and used to evaluate: (1) RCD by filtration on polycarbonate membrane, (2) plasma viscosity, and (3) erythrocyte phospholipid composition. Energy charge of red cell was evaluated by ATP/AMP/ADP and two to three DPB assays. Gas liquid chromatography indicated an increase in n-3 PUFA membrane erythrocyte composition. In the control group, RCD decreased by an average of 53% after exercise under hypoxic conditions and was unchanged after the same exercise at sea level. MaxEPA diet suppresses the decrease in RCD observed after hypoxic exercise. These results indicate a decrease in RCD under the combined effects of exercise and hypoxia, which is prevented by 6 weeks of fish oil supplement.

ADP plays a key role in thrombogenesis in rats.

The relative importance of ADP, arachidonic acid metabolites and serotonin as thrombogenic factors was evaluated in rats by comparing, after oral administration, the effects of two inhibitors of ADP-induced platelet aggregation (ticlopidine and PCR 4099), three cyclo-oxygenase inhibitors (aspirin, triflusal and indobufen) and a selective serotonin 5HT2 receptor antagonist (ketanserin) on platelet aggregation, in four platelet-dependent thrombosis models and on bleeding time. Platelet aggregation induced by ADP and collagen was completely inhibited by ticlopidine and PCR 4099 whereas only the collagen aggregation was reduced by the cyclo-oxygenase inhibitors. Ketanserin or a depletion of platelet serotonin by reserpine did not affect platelet aggregation. Ticlopidine and PCR 4099 greatly prolonged rat tail transection bleeding time. This is probably related to their known ability to inhibit ADP-mediated platelet aggregation. In contrast, the cyclooxygenase inhibitors did not affect bleeding time at all. Reserpine and ketanserin prolonged bleeding time by interfering with the action of serotonin on the vascular wall. Ticlopidine and PCR 4099 were very potent antithrombotics in all the models. Aspirin, only at a high dose, inhibited poorly thrombus formation on a silk thread in an arterio-venous shunt, suggesting that the inhibition of cyclo-oxygenase was not responsible. Triflusal was inactive in all models while indobufen slightly reduced thrombus formation in the silk thread and metallic coil models. Ketanserin and reserpine reduced thrombus only in the metallic coil model. Thrombus formation was greatly reduced in fawn-hooded rats, which lack ADP in their platelet dense granules because of a genetic storage pool deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of platelet aggregation by viridans group streptococci.

The direct aggregation of platelets is thought to be an important event in the pathogenesis of viridans streptococcal endocarditis, but the mechanisms for platelet activation are unknown. We evaluated the processes by which two endocarditis-producing strains of viridans group streptococci activated human platelets in vitro, as measured by platelet cyclooxygenase activity, secretion, and aggregation. Addition of either streptococcal strain to platelets suspended in whole plasma resulted in a mean lag phase of 15.3 min, followed by platelet secretion and brisk aggregation. The lag phase duration was dependent on the platelet donor and appeared to be a function of direct platelet-bacterial interaction. Aggregation was partially inhibited by 20 muM [corrected] indomethacin and blocked completely by 1 mg of apyrase, an extracellular ADP hydrolase, per ml. Neither strain aggregated washed platelets suspended in Tyrode solution alone. However, both strains produced maximal aggregation when the platelet suspension was supplemented with 10% (final concentration) normal plasma. Studies with factor-deficient plasmas demonstrated that exogenous fibrinogen was required for aggregation. One or more additional plasma components were needed, which eluted with a molecular weight of 67,000 to 130,000 on gel permeation chromatography. These cofactors have not been described for other platelet agonists, which suggests that viridans streptococci may aggregate human platelets by a novel mechanism.

Prostaglandin endoperoxides, thromboxane A2 and adenosine diphosphate in collagen-induced aggregation of rabbit platelets.

1 A bioassay technique is described for simultaneously monitoring rabbit platelet aggregation with measurement of thromboxane A(2) (TxA(2)) and prostaglandins released in response to collagen or arachidonic acid (AA).2 Five imidazole derivatives were examined as inhibitors of thromboxane synthetase and compared with the effect of the cyclo-oxygenase inhibitor indomethacin; 1-(7-carboxyheptyl) imidazole was identified as the most potent and selective inhibitor of thromboxane synthetase and was used with indomethacin to investigate the relative contribution of the prostaglandin endoperoxides prostaglandin G(2) (PGG(2))/PGH(2) and TxA(2) in mediating platelet aggregation induced by collagen or AA.3 Platelet aggregation induced by a low concentration of collagen was abolished by indomethacin and carboxyheptylimidazole whilst in response to a high concentration or collagen only partial inhibition of aggregation occurred.4 The contribution of adenosine diphosphate (ADP) released from platelets during collagen or AA-induced aggregation was examined using the substrate/enzyme complex creatine phosphate/creatine phosphokinase (CP/CPK). The CP/CPK complex abolished aggregation induced by a low dose of collagen whilst aggregation to a high dose of collagen was only partially inhibited.5 Aggregation induced by a high dose of collagen was abolished by a combination of CP/CPK with indomethacin or carboxyheptylimidazole.6 AA-induced aggregation was abolished by indomethacin. Carboxyheptylimidazole abolished aggregation induced by a low dose of AA but inhibition was surmounted with increasing concentrations of AA in the absence of TxA(2) formation.7 PGH(2)-induced aggregation was unaffected by indomethacin and only partially inhibited by carboxyheptylimidazole. AA or PGH(2)-induced platelet aggregation was unaffected by CP/CPK.8 In conclusion, aggregation of rabbit platelets induced by a low concentration of collagen was dependent on synergism between TxA(2) and ADP whilst at high concentrations of collagen, sufficient TxA(2) and ADP were released to induce aggregation independently of each other.9 The small amounts of prostaglandin endoperoxides produced from endogenous arachidonate have apparently no direct pro-aggregatory role. However, the relatively large amount which can be produced by a high concentration of exogenous AA when TxA(2) formation is prevented can cause aggregation of rabbit platelets.

Platelet - vessel wall interaction: role of blood clotting.

Vascular damage initiates not only the adhesion and aggregation of blood platelets but also coagulation, which is of mixed (intrinsic and extrinsic) origin. Evidence is presented that thrombin, generated as a result of the injury, is a prerequisite for platelet aggregation. Platelets, after activation, in their turn promote coagulation. Prostaglandin I2 (PGI2 or prostacyclin) inhibits coagulation induced by damaged vascular tissue. This effect of PGI2 is mediated by the inhibition of platelets in their participation in the generation of factor Xa and thrombin. Dietary cod liver oil, by changing plasma coagulability, decreases the procoagulation activity of vessel walls, and arterial thrombosis. Another fish oil with similar effects on plasma coagulability and some other haemostatic parameters does not modify vessel wall-induced clotting, nor does it significantly lower arterial thrombosis tendency; this indicates the physiological relevance of vessel wall-induced clotting in arterial thrombus formation. Some evidence is also given for the importance of vessel wall-induced clotting in primary haemostasis.

Carbenicillin and penicillin G inhibit platelet function in vitro by impairing the interaction of agonists with the platelet surface.

Carbenicillin or penicillin G administered in large doses can cause a bleeding diathesis as a result of platelet dysfunction. These antibiotics also inhibit platelet aggregation in vitro, although several-fold larger concentrations of drug are required to demonstrate this effect. We wondered whether these antibiotics might impair platelet function by interfering with the initial step of platelet activation: the binding of agonists to their specific receptors on the platelet surface.Platelet aggregation and [(14)C]serotonin release induced by epinephrine were competitively inhibited by carbenicillin and penicillin G in vitro. At antibiotic concentrations that inhibited platelet function by more than 80%, the affinity of platelet alpha-adrenergic receptors for the alpha-adrenergic antagonist, [(3)H]dihydroergocryptine, and for epinephrine was reduced twofold by carbenicillin and sixfold by penicillin G (P < 0.01). Platelet aggregation and [(14)C]serotonin release stimulated by ADP were also competitively inhibited by these antibiotics. In addition, carbenicillin reduced the incorporation of an ADP affinity label, 5'-p-fluorosulfonylbenzoyl [(3)H]adenosine, into its binding protein in platelet membranes. Moreover, both carbenicillin and penicillin G impaired the interaction of von Willebrand factor with platelets as evidenced by their inhibition of the agglutination of formalin-fixed platelets by ristocetin, snake venom, or bovine factor VIII. These studies demonstrate that carbenicillin and penicillin G inhibit platelet function in vitro by impairing the interaction of several agonists with their specific receptors on the platelet surface membrane. If this were mechanism operative in vivo, it could account for the hemorrhagic as well as the potential antithrombotic effects of these antibiotics.