Cigarette-Smoking Effect on Platelet Function

Age, cardiovascular risk factors and coronary heart disease as determinants of platelet function in men. A multivariate approach

Older age, the cardiovascular risk factors and arteriosclerosis have been reported to be associated with stimulated platelet function. To evaluate the relative importance of these factors in determining platelet function, a cross-sectional multivariate study in 191 men, 113 healthy subjects and 78 patients with angiographically documented coronary heart disease, was performed. In healthy subjects, stepwise multiple linear regression identified age to be a major determinant of platelet aggregability. After induction with both ADP and collagen the platelet aggregatory response markedly increased with age. In the patients, platelet function was not age dependent. In multivariate analysis of variance, neither smoking status nor hypercholesterolemia (greater than or equal to 240 mg/dl) were determinants of platelet function in either group. An increase in systolic blood pressure was associated with slightly more inhibited ADP induced aggregation in both healthy subjects and patients with coronary heart disease. In patients compared to healthy subjects, aggregation after induction with ADP and collagen was markedly enhanced and the in vitro formation of thromboxane after collagen stimulation increased. Thus, by multivariate analysis, age and the presence or absence of coronary heart disease were found to be major determinants of platelet function. In contrast, the cardiovascular risk factors smoking, hypercholesterolemia and hypertension were associated with only minor or no alterations of platelet function.

Sustained-release nifedipine (nifedipine-L) suppresses plasma thromboxane B2 and 6-keto prostaglandin F1 alpha in both young male smokers and nonsmokers

Sustained-release nifedipine (nifedipine-L) (40 mg twice a day) was administered orally to healthy young adult male smokers and nonsmokers for 10 days, and its effects on platelet aggregation, beta-thromboglobulin and platelet factor 4 levels, and plasma thromboxane B2 (TxB2) and 6-ketoprostaglandin F1 alpha (6-Keto-PGF1 alpha) concentrations were studied. The plasma nifedipine-L concentration in smokers (46.0 +/- 7.4 ng/ml) was significantly lower than that in nonsmokers (88.2 +/- 1.2 ng/ml). Nifedipine-L did not affect platelet aggregation induced by adenosine diphosphate, collagen, or epinephrine in either smokers or nonsmokers. The plasma beta-thromboglobulin level on the tenth day of nifedipine-L administration in nonsmokers was lower than that in smokers, but there were no significant differences either with or without nifedipine-L or between nonsmokers and smokers. Nifedipine-L had no effect on the concentration of platelet factor 4 in either smokers or nonsmokers. On the other hand, nifedipine-L significantly decreased the plasma TxB2 and 6-keto-PGF1 alpha concentrations in both smokers and nonsmokers. Thus we concluded that nifedipine-L suppressed the production of plasma TxB2 from platelets and also subsequently suppressed the production of 6-keto-PGF1 alpha and that this action was not affected by cigarette smoking.

Whole blood aggregation and plasma lyso-PAF related to smoking and atherosclerosis

1. Aggregation of diluted whole blood (impedance method) and thromboxane B2 production during aggregation were measured in cigarette smokers and non-smokers, aged 41-68 years, with (n = 14) and without (n = 15) major symptomatic peripheral vascular disease. The plasma level of the lyso derivative of platelet activating factor (lyso-PAF) was also measured using a bioassay with 14C-serotonin labelled rabbit platelets, after extraction and acetylation to active PAF. 2. Aggregation to ADP and collagen was significantly less in non-smokers without vascular disease (n = 8) than in the other three groups (P less than 0.01; ANOVA). Thromboxane B2 production was not significantly different between the groups. There was no significant difference in plasma lyso-PAF between groups. No change was found in any variable after smokers smoked two cigarettes. 3. In these older age subjects, both vascular disease and the smoking habit were associated with greater whole blood aggregation. However, current smoking and the smoking of two cigarettes did not affect aggregation in subjects with vascular disease and plasma lyso-PAF levels were not consistently related to either smoking or vascular disease.

No acute effect of cigarette smoking on bleeding time of habitual smokers

To study the influence of cigarette smoking on blood platelet function, bleeding time was measured in two groups of 14 habitual smokers before and after a 20-minute period during which the subjects either smoked two cigarettes (experimental group) or rested (control group). The second bleeding time appeared to be slightly shortened upon cigarette-smoking (-0.1 min) and was found to be prolonged in the control group (+0.4 min). These changes did not differ significantly from each other (P = 0.38). Consequently, bleeding time of habitual smokers is not affected by smoking two cigarettes.

Whole blood platelet aggregation is not affected by cigarette smoking but is sex-related

1. In normal subjects, 18-49 years old, the effects of the smoking habit (greater than 10 cigarettes/day) and the act of smoking two cigarettes over 10 min were studied on whole blood platelet aggregation (in vitro impedance method). 2. Acute smoking (n = 10) did not affect platelet aggregation to ADP, collagen or to platelet activating factor (PAF) nor thromboxane B2 production during aggregation. There was no difference between smokers (n = 13) and non-smokers (n = 10). However, aggregation to all aggregants was greater in females (n = 11) than males (n = 12) (ADP and collagen, P less than 0.001; PAF, P less than 0.01; ANOVA). 3. Although others have obtained diverse results studying platelet-rich plasma, the absence of an effect of cigarette smoking on whole blood platelet aggregation is consistent with many of those observations. Greater in vitro aggregability in females than males is consistent with the few studies of platelet-rich plasma. It seems unlikely that the role of cigarette smoking as a risk factor for ischaemic heart disease is related to a direct effect on platelet aggregability.

Evaluation of platelet function in pregnancy. Comparative studies in non-smokers and smokers

We have evaluated the possible role of platelet functional abnormalities as a contributory cause of thrombosis during pregnancy and to the increased fetal mortality and morbidity among women who smoke. Fifty-three pregnant women were enrolled and evaluated on two separate prenatal visits held between the 20th and 36th week of pregnancy and, when possible, post partum. Smoking status was evaluated by personal statement and alveolar carbon monoxide levels. Women in the smoking group deliberately avoided cigarettes for at least 20 minutes before sampling. Plasma levels of beta-thromboglobulin, thromboxane B2, and 6-Keto PGF1 alpha were evaluated. A significant increase in 6-Keto PGF1 alpha was noted among smoking women as pregnancy advanced. 6-Keto PGF1 alpha levels decreased among non-smoking women while beta-thromboglobulin increased significantly between the 20th and 33rd week of pregnancy in non-smokers. Platelet aggregation, both in platelet rich plasma and in whole blood (by impedance aggregometry), was evaluated by five different parameters and four different aggregating agents. Significant differences between the non-smoking and smoking pregnant women were noted for selected age cohorts and aggregating agents. An increase in platelet reactivity among smokers was observed in whole blood by impedance aggregometry with adenosine diphosphate and in two age cohorts using platelet rich plasma. In two groups in which aggregation was significantly accelerated among non-smokers, epinephrine was used as the aggregating agent.

Effects of chronic smoking on platelet function

Platelet function was investigated in 20 healthy cigarette smokers and 23 nonsmokers. Cigarette consumption was 1.4 +/- 0.5 packs/day (mean +/- SD) and the duration of smoking was 19 +/- 12 years. Platelet surface activation in vitro, aggregation in vivo and in vitro, as well as the release of platelet-specific proteins in vivo were evaluated. The mean number of platelet aggregates counted on an activating surface (Formvar film) was higher in smokers (80 +/- 59) than in nonsmokers (43 +/- 27) (P less than .01), indicating enhanced activity following exposure to an activating surface. Smokers who were 50 years of age or older showed an enhanced platelet aggregation following an in vitro stimulation in comparison to younger smokers (105 +/- 54 vs 54 +/- 55 aggregates) (P less than .05). Those who smoked 20 years or more also showed enhanced aggregation in comparison to those who smoked less than 20 years (112 +/- 60 vs 53 +/- 45 aggregates) (P = .02). Circulating platelets showed no significant difference among smokers and nonsmokers in the following tests: platelet aggregate ratio (0.67 +/- 0.30 vs 0.86 +/- 0.76), platelet count per mm3, (310,000 +/- 82,000 vs 278,000 +/- 78,000/mm3), levels of platelet factor 4 (9.8 +/- 5.2 vs 9.4 +/- 5.3 ng/ml), and plasma concentrations of beta-thromboglobulin (53.9 +/- 23.5 vs 49.1 +/- 25.5 ng/ml). The data suggest that chronic smoking primes platelets, causing them to aggregate more readily when exposed to an activating stimulus in vitro.

Physiological concentrations of epinephrine potentiate thromboxane A2 release from platelets in the isolated rat heart

The isolated rat heart perfused with washed platelets was used as a model to examine platelet-vessel wall interactions. Release of prostacyclin and thromboxane A2 was measured, using a cascade of smooth muscle bioassay tissues or radioimmunoassays of the stable hydration products. In hearts perfused with rabbit or human platelets, injection of sodium arachidonate caused release of both prostacyclin and thromboxane A2. In hearts perfused with aspirin-pretreated platelets, arachidonate released only prostacyclin indicating that thromboxane A2 originates largely in the platelets. Infusion of epinephrine (0.6-6 nmol/liter) through the heart potentiated arachidonate-induced release of thromboxane A2. Similar potentiation of thromboxane A2 release was observed in rat hearts perfused with either rabbit or human platelets, and in rabbit hearts perfused with rabbit platelets. In contrast, when rabbit platelets were infused through an incubation coil of tubing in place of the heart, epinephrine did not alter thromboxane A2 release. There was no significant loss of rabbit platelets on perfusion through rat hearts, and no aggregates were observed in the effluent either before or immediately after arachidonate injections, even in the presence of epinephrine. Thus, potentiation of thromboxane A2 production could not be explained by aggregation. However, it is clear from these studies that physiological concentrations of epinephrine can potentiate thromboxane A2 release from platelets when they are stimulated by arachidonic acid within the heart. This could result from a redirection of arachidonate metabolism to a local potentiating factor in the vessel wall. Potentiation of thromboxane A2 release might contribute to myocardial ischemia associated with platelet activation.

Cigarette smoking and platelet adhesion

Non-abraded rabbit endothelium has been exposed to human blood taken from male non-smoking volunteers before and after the smoking of two medium tar cigarettes, in an in vitro system using a Baumgartner chamber. In each case the blood was allowed to circulate for 10 min at a constant flow rate. Blood from 10 volunteers has been tested in this way. Scanning electron microscopy of the endothelial surfaces demonstrates large numbers of adherent platelets when 'post-smoking blood' is used, but very few and in some cases none with the 'pre-smoking' blood. As a further control to ensure that this phenomenon did not occur as a result from changes in the vessel related to the time during which it had been removed from its normal physiological environment, blood from further non-smoking volunteers was passed over seven of the remaining pieces of vessel at the completion of these runs. Platelets were either absent or very few in number, as with the pre-smoking samples.

The measurement of plasma thromboxane B2 and the effect of smoking

Plasma thromboxane B2 (TxB2) was measured by radioimmunoassay using an iodinated ligand following extraction and further purification by thin layer chromatography. Venous blood was sampled into a syringe containing the cyclooxygenase inhibitor meclofenamate. Normal levels, 15 pg/ml (s.d. = 8, n = 21), were lower than usually reported and measured values increased several fold over 20 min sampling from an indwelling needle. With appropriate sampling there was a statistically insignificant increase in plasma TxB2 after subjects smoked two cigarettes (n = 11). An average decrease occurred in a control group (n = 10) and the difference between groups was of borderline significance (P less than 0.05). Smoking did not change TxB2 production associated with platelet aggregation induced in vitro by collagen, whereas plasma adrenaline increased significantly. The results emphasize the importance of the technique of sampling and assay in the measurement of plasma TxB2.

Inhibition of platelet ADP and serotonin release by carbon monoxide and in cigarette smokers

The release of 14C-serotonin by ADP, epinephrine and arachidonic acid and the release of ADP by kaolin were measured in normal platelets in the presence and absence of carbon monoxide and in smokers' platelets. It is shown that carbon monoxide inhibits significantly the platelet release reaction. This function is also decreased in platelets obtained from heavy cigarette smokers.

Cigarette smoking shortens the bleeding time

The cutaneous bleeding time was shortened after smoking high nicotine cigarettes while not after smoking nicotine free cigarettes. The ADP induced primary platelet aggregation was not enhanced. The number of circulating platelet aggregates did not change due to smoking.

The effects of cigarette smoke and nicotine on platelet thrombus formation in stenosed dog coronary arteries: inhibition with phentolamine

This study was undertaken to examine in vivo the effects of cigarette smoke on cyclic reductions in coronary flow due to platelet thrombus formation in the stenosed coronary arteries of anesthetized dogs. The circumflex coronary artery of 21 mongrel dogs was stenosed 60 - 80%, with blood flow measured with an electromagnetic flow probe. After the administration of cigarette smoke, plasma epinephrine was elevated nine times the control level (p less than 0.001) and peak mean blood pressure was elevated one and one-half times control (p less than 0.01). The hematocrit increased several percent (p less than 0.01) with cigarette smoke, although blood gases and pH remained unchanged. In all 21 dogs, spontaneous reductions in coronary blood flow were greatly exacerbated in the stenosed circumflex artery as evidenced by the number of flow reductions, the increased size of the reductions and the rate of flow reduction. Nicotine administered intravenously in doses comparable to those achieved through absorption of cigarette smoke by the lungs provoked similar responses of alpha-adrenergic stimulation and potentiation of the platelet thrombus formation. An alpha-adrenergic antagonist, phentolamine, was given (3 mg/kg) intravenously to inhibit the exacerbated platelet thrombus formation due to cigarette smoke or infused nicotine. In 18 of 21 dogs, an acute occlusive platelet thrombus was prevented 15 minutes after phentolamine and after phentolamine and after a cigarette smoke or nicotine challenge. This study confirms a link between cigarette smoking, platelet formation, and the potential for humans to develop an acute occlusive platelet thrombus in a diseased and stenotic coronary artery.