Plasma levels of platelet secretory proteins

Heparin Resistance During Cardiopulmonary Bypass in Adult Cardiac Surgery

The use of heparin for anticoagulation has changed the face of cardiac surgery by allowing a bloodless and motionless surgical field throughout the introduction of cardiopulmonary bypass (CPB). However, heparin is a drug with complex pharmacologic properties that can cause significant interpatient differences in terms of responsiveness. Heparin resistance during CPB is a weighty issue due to the catastrophic consequences stemming from inadequate anticoagulation, and the treatment of it necessitates a rationalized stepwise approach due to the multifactorial contributions toward this entity. The widespread use of activated clotting time (ACT) as a measurement of anticoagulation during CPB is examined, as it may be a false indicator of heparin resistance. Heparin resistance also has been repeatedly reported in patients infected with COVID-19, which deserves further exploration in this pandemic era. This review aims to examine the variability in heparin potency, underlying mechanisms, and limitations of using ACT for monitoring, as well as provide a framework towards the current management of heparin resistance.

Platelet activation and placenta-mediated adverse pregnancy outcomes: an ancillary study to the Effects of Aspirin in Gestation and Reproduction trial

BACKGROUND

Platelet activation may play a role in the pathophysiology of placenta-mediated obstetrical complications, as evidenced by the efficacy of aspirin in preventing preeclampsia, but published data regarding the relationship between biomarkers for platelet activation and adverse obstetrical outcomes are sparse. In particular, it is unknown whether prepregnancy biomarkers of platelet activation are associated with adverse pregnancy outcomes.

OBJECTIVE

This study aimed to determine the following: (1) whether maternal plasma concentrations of platelet factor 4 are associated with risk of placenta-mediated adverse obstetrical outcomes, and (2) whether these associations are modified by low-dose aspirin.

STUDY DESIGN

This ancillary study included measurement of platelet factor 4 among 1185 of 1228 women of reproductive age enrolled in the Effects of Aspirin in Gestation and Reproduction trial with available plasma samples, with relevant outcomes assessed among 584 women with pregnancies lasting at least 20 weeks' gestation. We measured platelet factor 4 in plasma samples obtained at the prepregnancy study visit (before randomization to low-dose aspirin or placebo), 12 weeks' gestation, and 28 weeks' gestation. The primary outcome was a composite of hypertensive disorders of pregnancy, placental abruption, and small-for-gestational-age infant. We estimated the relative risks (RRs) and 95% confidence intervals (CIs) for the association between platelet factor 4 and the composite and individual outcomes at each time point using log-binomial regression that was weighted to account for potential selection bias and adjusted for age, body mass index, education, income, and smoking. To evaluate the potential effect modification of aspirin, we stratified the analyses by aspirin treatment assignment.

RESULTS

During follow-up, 95 women experienced the composite adverse obstetrical outcome, with 57 cases of hypertensive disorders of pregnancy, 35 of small for gestational age, and 6 of placental abruption. Overall, prepregnancy platelet factor 4 was positively associated with the composite outcome (third tertile vs first tertile; relative risk, 2.36; 95% confidence interval, 1.38-4.03) and with hypertensive disorders of pregnancy (third tertile vs first tertile; relative risk, 2.14; 95% confidence interval, 1.08-4.23). In analyses stratified by treatment group, associations were stronger in the placebo group (third tertile vs first tertile; relative risk, 3.36; 95% confidence interval, 1.42-7.93) than in the aspirin group (third tertile vs first tertile; relative risk, 1.78; 95% confidence interval, 0.90-3.50).

CONCLUSION

High concentrations of platelet factor 4 before pregnancy are associated with increased risk of placenta-mediated adverse pregnancy outcomes, particularly for hypertensive disorders of pregnancy. Aspirin may mitigate the increased risk of these outcomes among women with higher plasma concentrations of preconception platelet factor 4, but low-dose aspirin nonresponders may require higher doses of aspirin or alternate therapies to achieve obstetrical risk reduction.

Changes in heparin dose response slope during cardiac surgery: possible result in inaccuracy in predicting heparin bolus dose requirement to achieve target ACT

Introduction:

The substantial interpatient variability in heparin requirement has led to the use of a heparin dose response (HDR) technique. The accuracy of Hepcon-based heparin administration in achieving a target activated clotting time (ACT) using an HDR slope remains controversial.

Methods:

We prospectively studied 86 adult patients scheduled for cardiac surgery requiring cardiopulmonary bypass. The total dose of calculated heparin required for patient and pump priming was administered simultaneously to achieve a target ACT of 450 s for HDR on the Hepcon HMS system. Blood samples were obtained after the induction of anesthesia, at 3 min after heparin administration and after the initiation of CPB to measure kaolin ACT, HDR slope, whole-blood heparin concentration based on the HDR slope and anti-Xa heparin concentration, antithrombin and complete blood count.

Results:

The target ACT of 450 s was not achieved in 68.6% of patients. Compared with patients who achieved the target ACT, those who failed to achieve their target ACT had a significantly higher platelet count at baseline. Correlation between the HDR slope and heparin sensitivity was poor. Projected heparin concentration and anti-Xa heparin concentration are not interchangeable based on the Bland–Altman analysis.

Conclusion:

It can be hypothesized that the wide discrepancy in HDR slope versus heparin sensitivity may be explained by an inaccurate prediction of the plasma heparin level and/or the change in HDR of individual patients, depending on in vivo factors such as extravascular sequestration of heparin, decreased intrinsic antithrombin activity level and platelet count and/or activity.

Life in the shadow of a dominant partner: the FVIII-VWF association and its clinical implications for hemophilia A

A normal hemostatic response to vascular injury requires both factor VIII (FVIII) and von Willebrand factor (VWF). In plasma, VWF and FVIII normally circulate as a noncovalent complex, and each has a critical function in the maintenance of hemostasis. Furthermore, the interaction between VWF and FVIII plays a crucial role in FVIII function, immunogenicity, and clearance, with VWF essentially serving as a chaperone for FVIII. Several novel recombinant FVIII (rFVIII) therapies for hemophilia A have been in clinical development, which aim to increase the half-life of FVIII (∼12 hours) and reduce dosing frequency by utilizing bioengineering techniques including PEGylation, Fc fusion, and single-chain design. However, these approaches have achieved only moderate increases in half-life of 1.5- to 2-fold compared with marketed FVIII products. Clearance of PEGylated rFVIII, rFVIIIFc, and rVIII-SingleChain is still regulated to a large extent by interaction with VWF. Therefore, the half-life of VWF (∼15 hours) appears to be the limiting factor that has confounded attempts to extend the half-life of rFVIII. A greater understanding of the interaction between FVIII and VWF is required to drive novel bioengineering strategies for products that either prolong the survival of VWF or limit VWF-mediated clearance of FVIII.

The Platelet Aggregation Score and Its Correlation to β- Thromboglobulin and Platelet Factor 4 Levels

We describe a new method of interpreting platelet aggregometry results and its correlation to platelet secretory protein levels. We studied 123 healthy male volunteers, 37-85 years of age. The aggregation response to 2.5 μM ADP was measured in a standardized platelet suspension (SPS) prepared from platelet-rich plasma. Turbidimetic measurements included amplitude of the primary aggregation wave (Amp1), maximum aggregation amplitude (Amax), and area under the aggregation curve (Sagg). A platelet aggregation (PA) score was calculated as ( Amp1 /Amax) ·Sagg ·(whole-blood platelet count/SPS platelet count). β-Thromboglobulin (β-TG)and . platelet factor 4 (PF4) levels were measured by radioimmunoassay. The PA score correlated significantly (p < 0.0001) with β-TG ( r = 0.86) and PF4 ( r = 0.87). It was concluded that the PA score correlates closely with individual subjects' propensities to platelet activation, as reflected by plasma β-TG and PF4 levels. Key Words: Platelets-Platelet aggregometry-Platelet secretory proteins.

VEGF levels in plasma in relation to platelet activation, glycemic control, and microvascular complications in type 1 diabetes

OBJECTIVE

Increased levels of vascular endothelial growth factor (VEGF) in human plasma samples have suggested that circulating VEGF is a cause of endothelial dysfunction in diabetes mellitus. However, artificial release of VEGF from platelets as a source of VEGF in plasma samples, as also occurs in serum samples, has not been ruled out in these studies.

RESEARCH DESIGN AND METHODS

We determined VEGF levels in plasma collected in both citrate and PECT, a medium that inactivates platelets, in a cross-sectional cohort of 21 healthy subjects and 64 patients with type 1 diabetes. In addition, we evaluated whether VEGF levels in both types of plasma correlated with the presence of diabetes, glycemic control, markers of in vivo or ex vivo platelet activation, and degree of diabetic retinopathy and nephropathy.

RESULTS

VEGF levels were invariably low in PECT plasma of both nondiabetic and diabetic subjects and were unrelated to any other diabetes-related variable studied. In contrast, VEGF levels in citrate plasma were 150% higher in diabetic patients than in control subjects and correlated with diabetes-related variables. Multiple linear regression analysis showed that levels of platelet factor 4, a marker for ex vivo platelet activation, and HbA1c were the independent predictors of VEGF levels in citrate plasma. Platelet activation, in vivo and ex vivo, was similar in diabetic persons and control subjects.

CONCLUSIONS

Like serum, citrate plasma is not suitable for reliable measurements of circulating VEGF. The low levels of VEGF in vivo, as represented by measurements in PECT plasma in our study, do not support a role of circulating VEGF in endothelial dysfunction in type 1 diabetes. Higher levels of VEGF in citrate plasma samples of diabetic persons do not represent the in vivo situation, but mainly originate from higher artificial ex vivo release from platelets correlating with the degree of glycemic control.

Vascular endothelial growth factor in the circulation in cancer patients may not be a relevant biomarker

BACKGROUND

Levels of circulating vascular endothelial growth factor (VEGF) have widely been used as biomarker for angiogenic activity in cancer. For this purpose, non-standardized measurements in plasma and serum were used, without correction for artificial VEGF release by platelets activated ex vivo. We hypothesize that "true" circulating (c)VEGF levels in most cancer patients are low and unrelated to cancer load or tumour angiogenesis.

METHODOLOGY

We determined VEGF levels in PECT, a medium that contains platelet activation inhibitors, in citrate plasma, and in isolated platelets in 16 healthy subjects, 18 patients with metastatic non-renal cancer (non-RCC) and 12 patients with renal cell carcinoma (RCC). In non-RCC patients, circulating plasma VEGF levels were low and similar to VEGF levels in controls if platelet activation was minimized during the harvest procedure by PECT medium. In citrate plasma, VEGF levels were elevated in non-RCC patients, but this could be explained by a combination of increased platelet activation during blood harvesting, and by a two-fold increase in VEGF content of individual platelets (controls: 3.4 IU/10(6), non-RCC: 6.2 IU/10(6) platelets, p = 0.001). In contrast, cVEGF levels in RCC patients were elevated (PECT plasma: 64 pg/ml vs. 21 pg/ml, RCC vs. non-RCC, p<0.0001), and not related to platelet VEGF concentration.

CONCLUSIONS

Our findings suggest that "true" freely cVEGF levels are not elevated in the majority of cancer patients. Previously reported elevated plasma VEGF levels in cancer appear to be due to artificial release from activated platelets, which in cancer have an increased VEGF content, during the blood harvest procedure. Only in patients with RCC, which is characterized by excessive VEGF production due to a specific genetic defect, were cVEGF levels elevated. This observation may be related to limited and selective success of anti-VEGF agents, such as bevacizumab and sorafenib, as monotherapy in RCC compared to other forms of cancer.

Connective tissue growth factor is increased in plasma of type 1 diabetic patients with nephropathy

OBJECTIVE

Connective tissue growth factor (CTGF) is strongly upregulated in fibrotic disorders and has been hypothesized to play a role in the development and progression of diabetes complications. The aim of the present study was to investigate the possible association of plasma CTGF levels in type 1 diabetic patients with markers relevant to development of diabetes complications.

RESEARCH DESIGN AND METHODS

Plasma CTGF levels (full-length and NH2-terminal fragments) were determined in 62 well-characterized patients with type 1 diabetes and in 21 healthy control subjects. Correlations of these plasma CTGF levels with markers of glycemic control, platelet activation, endothelial activation, nephropathy, and retinopathy were investigated.

RESULTS

-Elevated plasma NH2-terminal fragment of CTGF (CTGF-N) levels were detected in a subpopulation of type 1 diabetic patients and were associated with diabetic nephropathy. Stepwise regression analysis revealed contribution of albuminuria, creatinine clearance, and duration of diabetes as predictors of plasma CTGF-N level. Elevation of plasma CTGF-N levels in patients with retinopathy was probably due to renal comorbidity.

CONCLUSIONS

Plasma CTGF-N levels are elevated in type 1 diabetic patients with nephropathy and appear to be correlated with proteinuria and creatinine clearance. Further studies will be needed to determine the relevance of plasma CTGF as a clinical marker and/or pathogenic factor in diabetic nephropathy.

Different patterns of heparin resistance: therapeutic implications

Heparin resistance (HR) during cardiac operations is a common feature. Its aetiology often recognizes a decrease in circulating antithrombin III (AT III) due to a preoperative heparin treatment. Nevertheless, some papers highlighted the existence of HR in patients with normal values of AT III. This paper was designed in order to identify this subgroup of AT III-independent heparin-resistant patients. Five hundred consecutive patients scheduled for coronary revascularization with cardiopulmonary bypass were enrolled in this prospective trial. HR was identified in 104 (20.8%) patients. Thirty-six of them (7.2% of the total population) had a preoperative AT III activity > or = 100%, and were defined as AT III-independent heparin-resistant patients. This subgroup significantly differs from the AT III-dependent heparin-resistant group being affected by a less severe degree of HR and including less patients pretreated with heparin. Unlike the other heparin-resistant patients, these subjects do not respond to AT III supplementation aimed at reaching supranormal AT III activity values.

Beta-thromboglobulin in urine and plasma: influence of coronary risk factors

Blood platelet activation in vivo was evaluated by measuring beta-thromboglobulin in plasma and high molecular weight beta-thromboglobulin in urine in hypertensive smoking and nonsmoking middle-aged men (n=36) and in normotensive age-matched controls (n=40). We found no significant linear relationships between nocturnal or resting urinary high molecular weight beta-thromboglobulin and plasma beta-thromboglobulin in the combined hypertensive and normotensive groups. The excretion of high molecular weight beta-thromboglobulin correlated significantly with diastolic blood pressure when all subjects were pooled. After 60 minutes supine rest, nonsmokers had higher excretion of high molecular weight beta-thromboglobulin than smokers. Plasma beta-thromboglobulin levels tended to be higher in hypertensives. In multivariate analyses, resting high molecular weight beta-thromboglobulin excretion was positively related to diastolic blood pressure and negatively related to smoking, whereas plasma beta-thromboglobulin was positively related to diastolic blood pressure and inversely related to apolipoprotein A1 and B. We conclude that urinary high molecular weight beta-thromboglobulin and plasma beta-thromboglobulin are not closely related, but are complementary analyses, as there are methodological confounders for both variables.

Hemostasis activation markers in acute renal failure

Fibrinopeptide A and thrombin-antithrombin III complex were used respectively as markers for in vivo thrombin formation and beta-thromboglobulin as a marker for platelet activation. In cases of acute renal failure (ARF) a heightened plasma concentration in the hemostasis activation markers may occur, because of a renal elimination disturbance, without a previous activation of the hemostasis. In order to check the validity of fibrinopeptide A, thrombin-antithrombin III complex and beta-thromboglobulin as markers for the hemostasis activation in cases of ARF we examined 32 patients prior to renal replacement therapy. A significant rise in fibrinopeptide A (x +/- SD: 34 +/- 22 ng/mL, ref < 3.0), thrombin-antithrombin III complex (19 +/- 15 ng/mL, ref 1.0-4.0) and beta-thromboglobulin (149 +/- 58 U/mL, ref 10-40) was found. None of the parameters examined showed a correlation to the serum creatinine. A correlation was observed respectively between fibrinopeptide A (r = 0.34, p < .05), beta-thromboglobulin (r = 0.39, p < .05) and the beta-thromboglobulin/creatinine coefficient (0.50 +/- 0.30, r = 0.72, p < .001) on the one side and the thrombin-antithrombin III complex on the other. A greater rise in the concentration of all parameters in patients with disseminated intravascular coagulation (DIC) was established, in contrast to patients without DIC (fibrinopeptide A: 44 +/- 31 vs. 32 +/- 20 ng/mL, beta-thromboglobulin: 169 +/- 57 vs. 144 +/- 60 U/mL, thrombin-antithrombin III complex 40 +/- 21 vs. 14 +/- 7 ng/mL, p < .05). Fibrinopeptide A and beta-thromboglobulin/creatinine coefficient in combination with the thrombin-antithrombin III complex can be employed as markers for the activation of hemostasis in cases of ARF there is no direct relationship between restricted kidney function in ARF and the plasma concentration of these markers, which behave similarly in spite of their varying elimination patterns.

Effects of hostility on platelet reactivity to psychological stress in coronary heart disease patients and in healthy controls

Previous studies have demonstrated a potential relationship between psychological stress and platelet activation, which may serve as a link between stress and myocardial infarction (MI). However, the possibility that personality traits associated with coronary heart disease may affect platelet activation has not been adequately investigated. The effect of a laboratory stressor (Type A Structured Interview (SI) and speech task) on platelet activation was assessed in 14 stable post-MI patients and 15 age-matched healthy men, using a standardized method of measuring plasma beta-thromboglobulin (BTG) levels. BTG levels were increased after the stressor (average change = 2.0 ng/ml, p = .005). Increases in BTG with stress were related to higher SI ratings of Potential for Hostility (r = .53, p = .004) and Type A behavior (r = .43, p = .02) but not to Cook-Medley-rated hostility scores. Increases in norepinephrine levels and in diastolic blood pressure were nonsignificantly related to increases in BTG levels (ps < .10), whereas increases in epinephrine levels were unrelated. Despite ceasing aspirin and other platelet inhibitors for 10 days before testing, individuals taking platelet inhibitors before the study had less change in BTG with stress (p = .05). However, after statistical adjustment for this factor, SI ratings of Potential for Hostility were still strongly related to increases in BTG with stress (adjusted r = .56, p = .002). Contrary to expectations, healthy men tended to have greater change in BTG with stress than post-MI patients (p = .06). These results indicate that acute stress increases BTG levels and that hostility is related to greater platelet reactivity, independent of any long term effects of platelet inhibition.

Time course of platelet alpha granule release in acute myocardial infarction treated with streptokinase

OBJECTIVE

To determine the time course of platelet alpha granule release in patients with acute myocardial infarction treated with streptokinase.

DESIGN

A prospective study.

SETTING

Coronary care unit.

PATIENTS

Nine with myocardial infarction treated with both streptokinase and aspirin, and nine with acute chest pain but without myocardial infarction, who were treated with aspirin only.

METHODS

All patients received 250 mg aspirin on admission and 150 mg once daily thereafter. All patients who fulfilled the indications for streptokinase received 1.5 megaunits, in a single infusion. After the initial medication, serial measurements of plasma beta thromboglobulin and plasma platelet factor 4 were performed at fixed intervals after the onset of chest pain. The primary endpoint sought was the peak value of beta thromboglobulin and platelet factor 4 in each individual.

RESULTS

The median peak plasma beta thromboglobulin in the infarction group was substantially higher than in those without infarction, at 37 (range 12 to 210) v 15 (9 to 36) mg/litre, P < 0.01. The corresponding values for plasma platelet factor 4 were 4.6 (2.4 to 60.0) v 2.2 (< 2 to 8.5) mg/litre, P < 0.01. Increased values were seen only within the first 12 h after onset of chest pain, and after 12 h there was no difference between the patients with myocardial infarction and those without. Aspirin treatment did not abolish alpha granule release.

CONCLUSIONS

In patients with acute myocardial infarction treated with streptokinase the content of the alpha granules is released within the first 12 h after the onset of chest pain. Aspirin apparently does not abolish this release.

The role of platelets in essential hypertension

Recent research is helping us understand the complex interactions that occur between platelets and their environment. The several intracellular events that occur during platelet activation are being identified as ar their effects on other platelets, the endothelium and coagulation factors. Heightened platelet activation is seen early in essential hypertension and probably plays an important role in the initiation and progression of atherosclerosis and the disorders associated with it. This review identifies some of the changes in platelet structure and function in essential hypertension and their role in the pathogenesis of hypertensive vascular disease.

Platelet alpha-granules

Platelets contain a vast number of biologically active molecules within cytoplasmic granules which are classified according to their respective distinct ultrastructures, densities and content. The alpha-granule is a unique secretory organelle in that it exhibits further compartmentalization and acquires its protein content via two distinct mechanisms: (1) biosynthesis predominantly at the megakaryocyte (MK) level (with some vestigial platelet synthesis) (e.g. platelet factor 4) and (2) endocytosis and pinocytosis at both the MK and circulating platelet levels (e.g. fibrinogen (Fg) and IgG). The currently known list of alpha-granular proteins continues to enlarge and includes many adhesive proteins (e.g. Fg, von Willebrand factor (vWf) and thrombospodin (TSP)), plasma proteins (e.g. IgG and albumin), cellular mitogens (e.g. platelet derived growth factor and TGF beta), coagulation factors (e.g. factor V) and protease inhibitors (e.g. alpha 2-macroglobulin and alpha 2-antiplasmin). More recently the inner lining of the alpha-granule unit membrane has been demonstrated to contain a number of physiologically important receptors including glycoprotein IIb/IIIa (alpha IIb beta 3) and P-selectin. The alpha-granules originate from small precursor granules which can be observed budding from the trans-Golgi network within the platelet precursor cell the MK. During MK maturation the alpha-granules become very prominent and are ultimately packaged into platelets during thrombopoiesis. The alpha-granular contents are destined for release during platelet activation at sites of vessel wall injury and thus play an important role in haemostasis, inflammation, ultimate wound repair and in the pathogenesis of atherosclerosis.

Platelet accumulation after laser angioplasty--a scintigraphic assessment

Indium 111-labeled platelet scintigraphy was performed to evaluate platelet deposition in response to different levels of Nd:YAG laser/thermal energy. A dose-related increase in platelet deposition was observed. In clinical studies after laser-assisted balloon angioplasty, intense platelet deposition was observed in 2 patients who subsequently developed clinical arterial thrombosis. The pathogenesis of reocclusion appears, however, to be more complicated and ill understood. The authors suggest further extensive studies incorporating several parameters in the evaluation of the pathogenic factors involved in reocclusion after laser angioplasty. Such studies should also consider the role of arterial injury produced by the balloon catheter after laser-assisted balloon angioplasty.

A new assay for beta-thromboglobulin in urine

Measurements of beta-thromboglobulin (beta TG) excretion in urine may be of value for "field" studies and due to problems with sampling artifacts for beta TG in plasma. Previous studies have used a radioimmunoassay designed for plasma without characterizing the "beta TG" immunoreactivity in urine. We describe modifications of the assay which increase its sensitivity and a sample work-up procedure using Sephadex G-25M columns separating high molecular weight (HMW) components (presumably intact beta TG) from low molecular weight (LMW) immunoreactivity (i.e. beta TG fragments and/or non-specific interferences). The sensitivity of the assay (with 2.5 ml sample) is less than 12 pg/ml HMW beta TG. Inter- and intraassay coefficients of variation were 7-10%. Only 33 (range 5-75)% of beta TG immunoreactivity in urine represented HMW beta TG. LMW immunoreactivity may be related to salt and other non-specific influences in the sample. Recoveries of beta TG were quite variable (9-100%) in unextracted urines, but high and reproducible (80 +/- 2%) in the HMW fraction. Thus, nonspecific interferences with beta TG measurements in certain urines are overcome by the separation step. Using Sephadex fractionation beta TG immunoreactivities in night urines (n = 15) were: 20 +/- 3 pg/ml in the HMW fraction, 70 +/- 8 pg/ml in the LMW fraction, and 85 +/- 10 pg/ml by direct assay. HMW beta TG increased in daytime samples (to 30 +/- 5 pg/ml; p less than 0.01), but no diurnal variation was seen in the LMW fraction or with the direct assay. Thus, selective analysis of HMW beta TG in urine circumvents problems with nonspecific immunoreactivity and apparent interferences with measurements of intact beta TG. The present more selective assay for HMW immunoreactivity increases the possibility of detecting physiological changes in beta TG release in vivo by urinary measurements.

Detection of arterial thrombosis after laser angioplasty by platelet scintigraphy

Indium-111-labelled platelet scintigraphy was performed in two patients after laser-assisted balloon angioplasty. Both patients demonstrated a significant 'hot spot' at the angioplasty site 24 h after successful recanalisation with laser and balloon. Clinically apparent thrombosis of the recanalised arteries occurred 5 and 6 days after angioplasty in both patients. Laser-assisted balloon angioplasty leads to significant platelet deposition over recanalised segments of the artery, which may result in arterial thrombosis, as evident from the reports presented. Indium-111-labelled platelet scintigraphy emphasises the extent of trauma caused by laser and balloon angioplasty to the arterial wall.

Platelet aggregability in humans: contrasting in vivo and in vitro findings during sympatho-adrenal activation and relationship to serum lipids

Platelet aggregability was studied in 18 healthy volunteers during mental stress (a colour word test; CWT) and low- and high-dose adrenaline infusions using an ex vivo technique (filtragometry) and conventional in vitro aggregometry. CWT and high-dose adrenaline (3.4 nmol l-1 in plasma) shortened filtragometry readings, suggesting increased platelet aggregability in vivo. Low-dose adrenaline had no effect despite higher adrenaline levels in plasma (0.9 nmol l-1) than during CWT (0.4 nmol l-1). Platelet sensitivity to ADP in vitro was reduced following CWT and further reduced following adrenaline infusions. In vitro, adrenaline (50 nmol l-1) had little effect on platelet aggregation per se, but enhanced aggregability evoked by ADP (at ED50). Adrenaline potentiation of ADP-induced aggregation was enhanced after CWT, but was not related to filtragometry responsiveness to stress in vivo. Serum LDL-cholesterol levels were inversely correlated to filtragometry readings at rest, suggesting an adverse influence on platelet aggregability in vivo. HDL-cholesterol levels were inversely correlated to platelet sensitivity to ADP in vitro, suggesting a positive influence. Thus, sympatho-adrenal activation enhances platelet aggregability in vivo (as assessed by ex vivo filtragometry), but adrenaline alone cannot explain the pro-aggregatory effect of mental stress. Serum lipoprotein alterations associated with increased risk for atherosclerosis seem to enhance platelet aggregability. The conventional in vitro technique may poorly reflect platelet aggregability in vivo.

Platelet release reaction and plasma catecholamines during total hip replacement. No effects of high doses of corticosteroids

Platelet activation and catecholamine levels during surgery and the effects of corticosteroids on these reactions were examined in fourteen patients operated by uncemented total hip replacement (THR). Beta-thromboglobulin (BTG), released from alpha granules during platelet activation, catecholamines and cortisol were examined in plasma before operation and in the early postoperative period. The patients were randomly divided into two groups, a corticosteroid group where the patients were treated by high doses of methylprednisolone (HDC) and a nonsteroid group. BTG increased about 200% during the operation, and thereafter, decreased to slightly supranormal values after 24 hours. There were no significant differences between the two patient groups. Catecholamine levels were low, and there were only minor changes following surgery. Cortisol increased following THR in the nonsteroid group. A standardized muscle-skeletal trauma in the form of THR caused a significant increase in platelet activation as evaluated by BTG increase during the first 24 hours after the operation. Catecholamines did not seem to be of importance for this activation, neither were the levels of BTG influenced by HDC.

Effect of dopamine and dopamine-antagonist infusion on blood platelet count, size and release reaction in hypertensive and normotensive subjects

To examine the effect of dopamine on in vivo platelet function and a possible platelet contribution to the clearance of dopamine we measured platelet count, platelet size and plasma concentration of the platelet specific protein beta-thromboglobulin (BTG) in groups of 40 year old untreated hypertensive and normotensive men. One hypertensive (n = 10) and one normotensive (n = 10) group received dopamine infusion at doses from 0.5 to 2.0 micrograms/kg/min which increased plasma dopamine 100-fold from baseline. Two other groups of hypertensive (n = 10) and normotensive (n = 11) subjects received 10 mg of the dopamine antagonist metoclopramide intravenously, upon which serum prolactin concentration increased 10-fold. No significant effect on platelet function in any group was observed during these interventions. Platelet phenol-sulphotransferase may contribute to dopamine conjugation. However, the selected platelet parameters correlated only weakly with dopamine kinetics during the infusion. Neither dopamine nor a dopamine antagonist altered the selected platelet parameters, nor did these parameters influence the clearance of dopamine during a short-lasting pharmacological infusion.