Differential expression of platelet activation markers in aspirin-sensitive asthmatics and normal subjects

BACKGROUND: Activation of platelets and expression of adhesion molecules (e.g. CD62P and CD63) which mediate interactions between platelets and other cells may be important in the pathogenesis of aspirin-sensitive asthma. OBJECTIVE: To determine the expression of CD62P and CD63 on platelets from aspirin-sensitive asthmatic (ASA+), aspirin-tolerant asthmatic (ASA-) and normal subjects and to assess the modulatory effect of aspirin on platelet CD62P and CD63 expression following stimulation with either platelet-activating factor (PAF), arachidonic acid (AA) or collagen (COL). METHODS: Platelet-rich plasma was obtained from 10 ASA+, 10 ASA- and 10 normal control subjects, and expression of CD62P and CD63 was measured by flow cytometry. Platelets were stimulated with PAF (10, 80 nM), AA (0.1, 1 mM) or COL (80, 800 micrograms/mL) with or without aspirin (concentration range 0.4-4 mg/mL). RESULTS: In the absence of aspirin, CD62P expression induced by AA and COL was greater in ASA+ patients compared with control subjects (P < 0.001) while CD62P expression with PAF, AA and COL was reduced in ASA- when compared with ASA+ and control subjects (P < 0.001). CD63 expression with PAF and AA was reduced in both ASA+ and ASA- patients compared with control subjects (P < 0.001). Aspirin inhibited the expression of both CD62P and CD63 after agonist stimulation. Greater inhibition of CD62P expression was observed in ASA+ compared with ASA- patients (P < 0.001) and normal subjects (P < 0.05) while greater inhibition of CD63 expression was observed in normal subjects compared with both ASA+ and ASA- patients (P < 0.05). In ASA+ patients and normal subjects, stimulation with PAF and COL resulted in only one platelet population while in contrast with 1 mM AA two populations were observed. CONCLUSIONS: Enhanced AA- and collagen-induced platelet CD62P expression in ASA+ patients compared with normal subjects and greater inhibition by aspirin of CD62P expression in ASA+ may be relevant to the pathogenesis of this syndrome. Reduced expression of CD62P and CD63 in platelets of ASA- patients following stimulation with PAF and AA may also have implications for the role of platelets and these mediators in the pathogenesis of other forms of asthma.     

Inhibition of platelet-vessel wall interactions by thromboxane receptor antagonism in a human in vitro system: potentiation of antiplatelet effects of aspirin

BACKGROUND: Pharmacological inhibition of arachidonic acid metabolism has proven therapeutically useful in the prevention of cardiovascular events. METHODS: We have investigated the ability of Bay u 3405, a synthetic thromboxane antagonist, to interfere with platelet aggregation and arachidonic acid metabolism. The antiplatelet action was also analysed in a perfusion system in which vascular subendothelium was exposed to circulating human blood (10 min; shear rate = 800 s-1). Platelet interactions were morphometrically analysed and results compared with those obtained in studies with blood from donors taking aspirin (acetylsalicylic acid, ASA) (500 mg day-1). The additional effect of Bay u 3405 on the antiplatelet action of ASA was also evaluated. RESULTS: Bay u 3405 caused a dose-dependent inhibition of platelet aggregation induced by U46619 with a maximal effect at concentrations > or = 0.01 microgram mL-1. Higher concentrations (> or = 0.05 micrograms mL-1) also inhibited aggregations induced by ADP or collagen. Bay u 3405 did not interfere with platelet arachidonic acid metabolism. In perfusion studies, Bay u 3405 (0.01 microgram mL-1) significantly decreased the total surface of the vessel covered by platelets (%CS = 18.7 +/- 1.09 vs. 24.4 +/- 1.94; P < 0.05) and the formation of large aggregates %T = 7.5 +/- 0.87 vs. 19.3 +/- 1.61; P < 0.01). ASA treatment reduced platelet aggregate formation (%T = 13.7 +/- 2.06; P < 0.05) but did not affect the total surface covered by platelets. The in vitro addition of Bay u 3405 to blood from ASA-treated donors further reduced the formation of large aggregates (%T = 2.7 +/- 0.79; P < 0.01 vs. ASA). CONCLUSIONS: In vitro effect of Bay u 3405 on platelet function were superior to those observed with ASA. The thromboxane antagonism antagonism provided by Bay u 3405 further enhanced the inhibition of platelet aggregate formation found after ASA treatment.     

The influence of dietary fatty acid composition on N-ethyl-N-nitrosourea-induced mammary tumour incidence in the rat and on the composition of inositol- and ethanolamine-phospholipids of normal and tumour mammary tissue

This study has investigated the influence of dietary fatty acid composition on mammary tumour incidence in N-ethyl-N-nitrosourea (ENU)-treated rats and has compared the susceptibility to dietary fatty acid modification of the membrane phospholipids phosphatidylinositol (PI) and phosphatidylethanolamine (PE) from normal and tumour tissue of rat mammary gland. The incidence of mammary tumours was significantly lower in fish oil--(29%), compared with olive oil--(75%; P < 0.04) but not maize oil--(63%; P < 0.1) fed animals. No differences in PI fatty acid composition were found in normal or tumour tissue between rats fed on maize oil, olive oil or fish oil in diets from weaning. When normal and tumour tissue PI fatty acids were compared, significantly higher amounts of stearic acid (18:0) were found in tumour than normal tissue in rats given olive oil (P < 0.05). A similar trend was found in animals fed on maize oil, although differences between normal and tumour tissue did not reach a level of statistical significance (P < 0.1). In mammary PE, maize oil-fed control animals had significantly higher levels of linoleic acid (18:2n-6) than either olive oil- or fish oil-fed animals (P < 0.05, both cases) and levels of arachidonic acid were also higher in maize oil- compared with fish oil-fed animals (P < 0.05). In tumour-bearing animals no differences in PE fatty acid composition were found between the three dietary groups. When normal and tumour tissue PE fatty acids were compared, significantly lower amounts of linoleic acid (18:2n-6; P < 0.01) and significantly greater amounts of arachidonic acid (20:4n-6; P < 0.05) were found in tumour than normal tissue of rats fed on maize oil. The present study shows that the fatty acid composition of PI from both normal and tumour tissue of the mammary gland is resistant to dietary fatty acid modification. The PE fraction is more susceptible to dietary modification and in this fraction there is evidence of increased conversion of linoleic acid to arachidonic acid in tumour compared with normal tissue. Lower tumour incidence rates in rats given fish oils may in part be due to alteration in prostanoid metabolism secondary to displacement of arachidonic acid by eicosapentaenoic acid, but PE rather than PI would appear to be the most likely locus for diet-induced alteration in prostanoid synthesis in this tissue. Effects of dietary fatty acids other than on the balance of n-6 and n-3 fatty acids, and on prostanoid metabolism, should also be considered. The significance of increased stearic acid content of PI in tumours of olive oil-fed animals and the possible influence of dietary fatty acids on the capacity for stearic acid accumulation requires further study.     

The effect of thrombin on the uptake and transformation of arachidonic acid by human platelets

Washed human platelets take up arachidonic acid from plasma and incorporate the fatty acid into the major classes of complex lipids. Thrombin impairs net incorporation. It activates endogenous phospholipases which liberate arachidonic acid from phospholipids. As a consequence of thrombin induced aggregation platelets release arachidonic acid intermediates formed by the action of platelet fatty acid cyclooxygenase and by platelet fatty acid lipoxygenase. Cyclooxygenase, but not lipoxygenase, is inhibited by aspirin and indomethicin. Analysis of the pathways of arachidonic acid metabolism may furnish new insight into platelet function and into disorders of primary hemostasis.     

Heat shock proteins and arthritis--new readers start here

We have characterised G protein and fatty acid regulation of the Na+ conductance in purified apical membrane vesicles prepared from late gestation fetal guinea-pig lung. Addition of 100 microM GTP gamma S or beta gamma-methylene-GTP, irreversible G protein activators, stimulated conductive 22Na+ uptake (ratio of experimental to control 1.35 +/- 0.02 and 1.34 +/- 0.05, respectively). Conversely, the addition of GDP beta S, an irreversible G protein inhibitor, reduced conductive 22Na+ uptake from 1.00 (control) to 0.79 +/- 0.04. A range of saturated (myristic, palmitic, stearic), monounsaturated (elaidic, oleic) and polyunsaturated (linoleic, arachidonic) fatty acids all stimulated conductive 22Na+ uptake, by between 1.18 +/- 0.05 to 1.56 +/- 0.13 over the control. Both arachidonic acid and GTP gamma S-dependent stimulation were abolished in the presence of 10 microM amiloride. The non-metabolisable analogue of arachidonic acid, eicosa-5,8,11,14-tetraynoic acid also stimulated conductive 22Na+ uptake. Furthermore, addition of indomethacin and nordihydroguairetic acid, inhibitors of cyclooxygenase and lipoxygenase pathways of arachidonate metabolism respectively, did not affect the arachidonic acid stimulation suggesting a direct effect of fatty acid upon the Na+ channel Since mepacrine (50 microM), a phospholipase A2 inhibitor, did not affect the GTP gamma S-stimulated conductive 22Na+ uptake, and inhibition of G protein turnover by GDP beta S did not attenuate the arachidonic acid response we conclude that these two regulatory pathways modulate alveolar Na+ transport directly and independently of each other.     

Hyaluronic acid inhibits fetal platelet function: implications in scarless healing

Platelets are important for the initiation of inflammation in adults, but the role of fetal platelets in fetal wound healing is unclear because fetal dermal wounds heal with a minimal inflammatory response and lack of excessive scarring. Because fetal tissue is abundant in glycosaminoglycans (GAGs), predominantly hyaluronic acid (HA), this study was designed to test the hypothesis that HA inhibits the reactivity of platelets and thus contributes to the minimal scarring characteristic of fetal tissue repair. Platelets were isolated from 10 fetal pigs at day 80 of gestation (term, 115 days) and exposed to 0.5 mg/mL of arachidonic acid, an agent shown in prior studies to evoke maximal aggregation and degranulation of fetal platelets. The ability of HA at 0.1 and 0.5 mg/mL to inhibit this response was determined. The presence of HA resulted in a dose-dependent reduction in platelet aggregation at 180 seconds (control, 99.7 +/- 0.3%; HA [0.1 mg/mL] 91.7 +/- 3.8%; and HA [0.5 mg/mL] 48.5 +/- 9.0%; P < .005 v control). The onset of aggregation was also significantly delayed by 0.5 mg/mL of HA (13.5 +/- 2.5 seconds) compared to control (2.9 +/- 0.7 seconds), P < .05. No significant diminution of platelet aggregation could be achieved by the addition of other GAGs at similar concentrations. HA also significantly impaired the release of platelet-derived growth factor (PDGF)-AB from fetal platelets. The authors conclude that HA, the predominant GAG in fetal dermal matrix, inhibits platelet aggregation and cytokine release. This inhibition of platelet aggregation and resultant inflammatory response may explain, in part, the minimal inflammation and scarless healing characteristic of fetal dermal repair.     

Oxysterols and TBARS are among the LDL oxidation products which enhance thromboxane A2 synthesis by platelets

In this study, we compared the effects of normal LDL (nLDL) and oxidized LDL (oxLDL) on thromboxane (TXA2) release by platelets triggered by low concentration of thrombin, and we determined which component of oxLDL is responsible for that activation. After oxidation of LDL with copper sulfate, the small molecular weight fraction (< 10 kDa) which was high in TBARS was removed; using Amicon Centriprep-10 concentrator membrane. More than 67% of TBARS in the oxLDL preparation was found in solution while the remaining was covalently attached to the oxLDL particles. OxLDL contained significantly higher levels of oxysterols and TBARS than the nLDL. Platelets preincubated with low concentrations of oxLDL (33-132 micrograms protein/mL) produced significantly higher TXA2 than platelets preincubated with equivalent concentrations of nLDL when triggered with thrombin. Platelets treated with oxLDL also contained significantly higher levels of oxysterols than platelets treated with nLDL. Platelets preincubated with pure cholestanetriol (10 micrograms/mL) contained a high level of cholestanetriol in the membrane, and TXA2 release was significantly increased in these platelets compared to the control platelets. The TBARS in solution also was very potent in enhancing TXA2 release by thrombin-treated platelets. These results indicate that oxysterols and the free TBARS either in solution or covalently attached to the oxLDL particles are partly responsible for the stimulatory effect of oxLDL on TXA2 release by platelets. The present study also showed that this enhancement of TXA2 release was due to activation of phospholipase A2 and to the increase of arachidonic acid liberation from the platelet phospholipids.     

Transcellular activation of platelets and endothelial cells by bioactive lipids in platelet microparticles

Microparticles are released during platelet activation in vitro and have been detected in vivo in syndromes of platelet activation. They have been reported to express both pro- and anticoagulant activities. Nevertheless, their functional significance has remained unresolved. To address the mechanism(s) of cellular activation by platelet microparticles, we examined their effects on platelets and endothelial cells. Activation of human platelets by diverse stimuli (thrombin, 0.1 U/ml; collagen, 4 microg/ml; and the calcium ionophore A23187, 1 microM) results in shedding of microparticles. Pretreatment of these particles, but not membrane fractions from resting platelets, with (s)PLA2 evokes a dose-dependent increase in platelet aggregation, intracellular [Ca2+] movement, and inositol phosphate formation. These effects localize to the arachidonic acid fraction of the microparticles and are mimicked by arachidonic acid isolated from them. However, platelet activation requires prior metabolism of microparticle arachidonic acid to thromboxane A2. Thus, pretreatment of platelets with the cyclooxygenase (COX) inhibitor, indomethacin (20 microM), the thromboxane antagonist SQ29,548 (1 microM), or the protein kinase C inhibitor GF109203X (5 microM) prevents platelet activation by microparticles. However, platelet microparticles fail to evoke an inositol phosphate response directly, via either of the cloned thromboxane receptor isoforms stably expressed in human embryonic kidney (HEK) 293 cells. Prelabeling platelets with [2H(8)] arachidonate was used to demonstrate platelet metabolism of the microparticle-derived substrate to thromboxane. Platelet microparticles can also induce expression of COX-2 and prostacyclin (PGI2) production, but not expression of COX-1, in human endothelial cells. These effects are prevented by pretreatment with actinomycin D (12 microM) or cycloheximide (5 microg/ml). Expression of COX-2 is again induced by the microparticle arachidonate fraction, which it may then use to synthesize PGI2. Both PGE2 and iloprost, a stable PGI2 analog, evoke human umbilical vein endothelial cell COX-2 expression, albeit with kinetics that differ from the response to platelet microparticles. These studies indicate a novel mechanism of transcellular lipid metabolism whereby platelet activation may be amplified or modulated by concentrated delivery of arachidonic acid to adjacent platelets and endothelial cells.     

Platelet aggregability in patients with a VVI pacemaker

Several studies have suggested an increased incidence of thromboembolic events in patients with VVI pacemaker (VVI patients); furthermore, other authors have demonstrated that a treatment with anticoagulants or antiplatelet drugs may be effective in reducing thromboembolic events, thus suggesting an increased formation of platelet thrombi in these patients. In this respect, platelet aggregability was investigated in ten VVI patients and ten age- and sex-matched subjects. beta-thromboglobulin (beta-Tg) and platelet factor 4 (PF4) plasma levels were determined as well as platelet aggregation induced by ADP, collagen, epinephrine, and arachidonic acid. Plasma beta-Tg levels were increased in the patient group (86 +/- 24 vs 24 +/- 13 ng/mL; P < 0.001) in presence of normal PF4 values (14 +/- 11 vs 13 +/- 6 ng/mL; NS). Aggregation curves showed abnormal values of maximal amplitude, slope, and lag time. In particular, maximal amplitude was significantly higher in VVI patients as compared with controls (ADP P < 0.01, collagen P < 0.001, adrenaline P < 0.01, arachidonic acid P < 0.05). These findings strongly suggest an increase of platelet activity in VVI patients.     

Increased synthesis of prostaglandin-E-like material by platelets from patients with diabetes mellitus

We studied the effects of ADP, epinephrine, collagen and arachidonic acid on platelet production of immunoreactive prostaglandin-E-like material and aggregation in 17 subjects with diabetes mellitus and 21 matched controls. Plateletrich plasma obtained from patients synthesized significantly (P less than 0.05) greater quantities of the prostaglandin-E-like material after exposure to 1 muM ADP, 1, 2 and 5 muM epinephrine and 1 microgram per milliliter of collagen than platelet-rich plasma obtained from controls. That obtained from the diabetic patients was significantly more sensitive (P less than 0.001) to the aggregating effects of the prostaglandin precursor, arachidonic acid, in vitro as compared to controls. Diabetic platelet-rich plasma metabolized arachidonic acid (0.5 mM) to immunoreactive prostaglandin-E-like material at a significantly greater rate (P less than 0.05) and extent (P less than 0.001) than that of controls. Thus, platelets obtained from diabetic patients possess increased activity of the prostaglandin synthetase system, and this characteristic may be related to the increased platelet aggregation associated with the disease.     

Colchicine poisoning apropos of a pediatric case

The activity of trapidil, an antiaggregating agent with PDGF antagonist properties, was investigated in order to verify its possible modulating effect in the endothelial and platelet activation. PDGF, t-PA, PAI-1 and ET-1 plasma levels were measured before and after a 2 month treatment period with trapidil 200 mg tablets bid or placebo in 30 patients affected by POA in Fontaine stage II. PDGF and PAI-1 significantly (p < 0.05) increased in the placebo group, and PDGF also in the comparison between treatments (p < 0.05). Aggregation data demonstrate an absence of Ca++ antagonist action of trapidil. The results of this study suggest that trapidil can interfere with the combined vascular and platelet response in atherogenesis.     

Functional status of thrombocytes in men and women in younger age groups

Differences in the functional status of platelets in vitro were compared between young adult men and women. Platelets in women were found to have a higher susceptibility to ADP, epinephrine, arachidonic acid and to produce more TXB2. These changes appear to be due to the declined hematocrit and thus to lower concentrations of sodium citrate, a commonly used anticoagulant. Platelet activity was conversely related to plasma sodium citrate. Since calcium chloride was found to offset the inhibitory effect of sodium citrate, it was assumed that the sex-related differences observed in platelet activity were due to varied levels of ionized calcium. The platelet activity was at equal values of hematocrit equal in both sexes. (Tab. 3, Ref. 19.).     

Which operations can be done without general anesthesia?

The fatty acid composition of erythrocytes, platelets, and serum lipids was compared between subjects who had been eating a strict uncooked vegan diet ("living food") for years and omnivore controls. The vegan diet contains equal amounts of fat but more monounsaturated and polyunsaturated and less saturated fatty acids than the mixed diet of the control group. In vegans, the proportion of linoleic acid was greater in all lipid fractions studied. Also, the levels of other n-6 fatty acids were greater, with the exception of arachidonic acid levels, which were similar in most fractions. In erythrocytes, platelets and serum phospholipid fractions, this increase was mainly at the expense of the n-3 fatty acids. The proportions of eicosapentaenoic and docosahexaenoic acid were only 29-36% and 49-52% of those in controls, respectively. In vegans the ratio of n-3 to n-6 fatty acids was only about half that in omnivores. In addition to the lower levels of n-3 fatty acids, the proportions of palmitic and stearic acids were lower in serum cholesteryl esters, triglycerides and free fatty acids of vegans. The proportion of oleic acid was slightly lower only in serum cholesteryl esters and erythrocyte phosphatidylserine. The results show that, in the long term, the vegan diet has little effect on the proportions of oleic and arachidonic acids, whereas the levels of n-3 fatty acids are depressed to very low levels with prolonged consumption of the high linoleic and oleic acid components of this diet.     

Multiple chemical sensitivities, including iatrogenic allergic contact dermatitis, in a patient with chronic actinic dermatitis: implications for management

In order to clarify the influence of inflammatory mediators of the arachidonic acid cascade in the mechanism of nasal polyp growth, peptido-leukotriene (pLT), prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) synthesis was investigated. In addition to several stimuli, functionally intact human biopsy specimens of polypous and normal tissue were incubated. Especially remarkable was the significantly increased release of pLT by polypous tissue upon arachidonic acid stimulation, in contrast to only slightly elevated PGE2 release compared to normal tissue. Basic release of pLT and PGE2 was similar for polypous and normal tissue. Examining TXB2 release, no significant difference was observed with regard to the origin of tissues. These data support an altered pattern of the lipoxygenase and cyclo-oxygenase pathways when tissue becomes irritated and suggest their involvement in the aetiopathogenesis of nasal polyps.     

Ganglioside content of human platelets--differences in resting and activated platelets

Gangliosides may play functional roles in platelet physiology, therefore this study has been designed to evaluate whether changes in ganglioside composition may occur as a consequence of platelet activation. The results obtained indicate that lactosylceramide and GM3 are the major glycosphingolipids of human platelets. The lipid-bound sialic acid (LBSA) content was 1.27 +/- 0.04 micrograms/mg of protein. Resting platelets did not express GD3; GD3 was synthesized upon platelet activation (24 +/- 8 ng/mg of protein). The stimulation of platelets with adenosine diphosphate showed the appearance of GD3 even in the absence of degranulation. Finally, incorporation of pyrene-labeled GM3 into platelet membranes, followed by stimulation with adenosine diphosphate, resulted in the appearance of a fluorescent band comigrating with GD3. The present studies indicate that sialytransferase activation may occur as an early event following platelet stimulation, leading to GD3 synthesis mainly from the GM3 pool.     

Galactose-specific lectin from Viscum album as a mediator of aggregation and priming of human platelets

Galactose-specific lectin from Viscum album (VAA) was found to induce aggregation of human platelets in a dose- and sugar-dependent manner. Small nonaggregating concentrations of VAA primed the response of platelets to known aggregants (ADP, arachidonic acid, thrombin, ristocetin, and A23187). VAA-induced platelet aggregation was completely reversible by addition of the sugar inhibitor lactose and the platelets from disrupted aggregates maintained the response to other aggregants. The lectin-induced aggregation of washed platelets was more resistant to metabolic inhibitors than thrombin- or arachidonic acid-dependent cell interaction. In contrast to the related galactose-specific lectin from Ricinus communis and the soy bean agglutinin, the lectin did not aggregate liposomes prepared from total platelet lipids, indicating different affinities of aggregation-mediating lectins to platelet glycolipids.     

The effect of a free radical scavenger and platelet-activating factor antagonist on FFA accumulation in post-ischemic canine brain

The effects of the platelet-activating factor antagonist BN 50739 and a free radical scavenger dimethyl sulfoxide on the accumulation of free fatty acids in post-ischemic canine brain are reported. Following 14 min of complete normothermic ischemia and 60 min of reperfusion, the total brain FFAs were approximately 150% higher than in the control group (p < 0.05). Perfusion with the platelet-activating factor antagonist BN50739 in its diluent dimethyl sulfoxide during 60 min of post-ischemic reoxygenation resulted in a 61.8% (p < 0.01) reduction in the total brain free fatty acid accumulation. Palmitic, stearic, oleic, linoleic, and arachidonic acids decreased by 53.8%, 63.5%, 69.0%, 47.4%, and 57.2%, respectively. Although dimethyl sulfoxide alone caused stearic and arachidonic acids to return to the normal concentration range, BN 50739 had a significant influence on recovery of palmitic, oleic, and linoleic acids and was previously shown to provide significant therapeutic protection against damage to brain mitochondria following an ischemic episode. Because free fatty acid accumulation is one of the early phenomena in cerebral ischemia, this study provides evidence to support the hypothesis that both platelet-activating factor and free radicals are involved in initiating cerebral ischemic injury.     

Ovarian sensitivity to exogenous gonadotrophins in phenobarbital treated unilaterally ovariectomized albino rats

To evaluate platelet activity in patients with non-insulin-dependent diabetes mellitus (NIDDM), we measured the mean platelet volume (MPV) and 24-hour urinary excretion of 11-dehydro-thromboxane B2 (11-dTXB2) and 6-keto-prostaglandin F1 alpha (6-kPGF1 alpha), stable metabolites of thromboxane A2 and prostacyclin, respectively. The MPV of the 103 subjects in the NIDDM group were 10.72 +/- 0.82 fl for males and 10.52 +/- 1.01 fl for females (mean +/- SD), significantly higher than those of normal controls (9.95 +/- 0.75 fl for males and 9.84 +/- 0.72 fl for females). The MPV of patients with NIDDM showed positive correlations with fasting plasma glucose level and HbA1c (r = 0.234, P < 0.05; r = 0.267, P < 0.01, respectively). The urinary excretion of 11-dTXB2 was greater in the NIDDM group (7.58 +/- 4.42 micrograms/day for males and 5.65 +/- 2.38 micrograms/day for females) than in the normal controls (4.61 +/- 2.31 and 3.83 +/- 1.60, respectively), suggesting that the synthesis of thromboxane A2 by platelets may be accelerated in vivo in patients with NIDDM. The urinary 6-kPGF1 alpha was not different between the NIDDM group and normal controls among the males, but was greater in the NIDDM group among the females. As MPV showed a positive correlation (r = 0.364, P < 0.05) with urinary excretion of 11-dTXB2, MPV may be related to platelet activity. These findings suggest that the platelets of patients with NIDDM may be in a hyperactive state.     

Long term effects of 50 mg acetylsalicylic acid alone and in combination with dipyridamole on platelet function after coronary bypass surgery

In a prospective randomized trial in 42 patients undergoing coronary artery bypass surgery, we analyzed the long term platelet inhibiting effects of 50 mg acetylsalicylic acid (ASA) by itself and in combination with dipyridamole (2 x 200 mg), in comparison with phenprocoumon. Three and six months therapy led to significant inhibition of maximum aggregation induced by collagen 1 microgram/ml in platelet rich plasma (PRP) by more than 50% (p < or = 0.05). In PRP stimulated with 5 micrograms/ml collagen maximum inhibition amounted to nearly 20% (n.s.). The groups treated with ASA/ASA + dipyridamole showed an ADP threshold concentration 2.5 times higher than the group treated with phenprocoumon (p < or = 0.05). After stimulation with collagen 1 microgram/ml and 5 micrograms/ml thromboxane B2 synthesis in vitro in both groups treated with ASA was reduced to 1% of the base line values (p < or = 0.01). Inhibition of aggregation in whole blood appeared evident, but was not statistically significant due to considerable fluctuation of measurement. An additional effect of dipyridamole was not detectable. In conclusion, treatment with 50 mg ADA/d results in a lasting, effective inhibition of aggregation of platelets in patients with coronary artery bypass surgery. There is no synergistic effect of additional dose of 400 mg dipyridamole/d.     

Detection of low numbers of neuroblastoma cells in vitro

AIMS: The aim of the study was to obtain further information regarding the modes of action of doxazosin, naftopidil and nifedipine on platelet function. METHODS: We conducted an in vitro study of drug influences on adrenaline and collagen-induced mobilization of platelet calcium. RESULTS: In the presence of fibrinogen (300 micrograms ml-1) both collagen (5 micrograms ml-1) and adrenaline (16 microM) stimulated the aggregation of washed platelets. Collagen induced a transient rise (+4.97 +/- 0.63 microM) in platelet Ca2+ concentration, [Ca2+]i, as measured using the photoprotein aequorin, which coincided with the onset of aggregation. Adrenaline induced a smaller rise (+3.6 +/- 0.96 microM) which, however, occurred after the onset of aggregation. Naftopidil, an alpha 1-adrenoreceptor antagonist produced a concentration-dependent inhibition of collagen-induced Ca2+ mobilization, maximum inhibition (22.9 +/- 4%, P < 0.05) occurring with 40 microM naftopidil. The inhibition of Ca2+ mobilization was not reflected by a concentration-dependent inhibition of platelet aggregation, although 40 microM naftopidil produced statistically significant inhibition (23.3 +/- 11.7%, P < 0.05). The adrenaline-induced rise in [Ca2+]i was inhibited dose dependently by naftopidil (e.g. 40 microM naftopidil, 100 +/- 0%, P < 0.05), as was aggregation (40 microM naftopidil, 100 +/- 0%, P < 0.05). Doxazosin, another alpha 1-adrenoreceptor blocker, inhibited Ca2+ mobilization induced by collagen to similar extents as for naftopidil (30 microM doxazosin, 17.4 +/- 2.5%, P < 0.05), but did not inhibit platelet aggregation. It also inhibited the adrenaline-induced rise in [Ca2+]i in a concentration-dependent manner (30 microM doxazosin, 37.6 +/- 13.7%, P < 0.05), significant inhibitions of platelet aggregation also being produced (30 microM, 49.6 +/- 17.2%, P < 0.05). As expected, the calcium channel blocker nifedipine produced concentration-dependent inhibitions of both collagen-induced Ca2+ mobilization (e.g. 28 microM nifedipine, 47.8 +/- 2.7%, P < 0.05) and aggregation (28 microM, 55.1 +/- 9.2%, P < 0.05). CONCLUSIONS: These data indicate that the alpha 1-adrenoreceptor blockers, naftopidil and doxazosin, inhibit Ca2+ mobilization, this mechanism being possibly the means whereby these drugs inhibit platelet aggregation.