Time Dependence of Whole Blood Aggregation in Response to Platelet Activating Factor (PAF)

The aggregation/adhesion response to platelet activating factor (PAF) was studied in diluted whole blood by impedance aggregometry. The extent of aggregation varied directly with the interval between blood sampling and aggregation measurement over the first 30 minutes from sampling, then remained stable for the next 60 minutes of observation. This is an effect opposite to that described for aggregation to PAF in platelet rich plasma which, however, cannot be studied soon after sampling. Time dependence of aggregation is important and comparative measurements should be made during the period of stable aggregability.

Short term vitamin E supplementation has no effect on platelet function, plasma phospholipase A2 and lyso-PAF in male volunteers

1. Based largely upon in vitro studies, vitamin E has been reported to inhibit phospholipase A2 activity, to alter phospholipid metabolism and reduce platelet aggregation. 2. The effect of dietary supplementation with D-alpha-tocopherol (1500 iu/day for 14 days) was studied in nine males, 41-63 years old, comparing active treatment with a preceding placebo period. 3. Despite an increase from 2.6 +/- 0.8 (s.d.) x 10(-5) mol/L to 6.0 +/- 1.8 10(-5) mol/L in plasma vitamin E there were no significant changes in the aggregation of diluted whole blood or platelet rich plasma to adenosine diphosphate (ADP) or collagen, in plasma phospholipase A2 activity or plasma lyso-platelet-activating factor (lyso-PAF) (bioassay after in vitro acetylation to PAF). 4. High dose vitamin E dietary supplementation had no effect on these phospholipid and platelet parameters.

Whole blood aggregation, thromboxane release and the lyso derivative of platelet activating factor in myocardial infarction and unstable angina

To investigate the pathophysiology of intracoronary thrombus formation we measured whole blood aggregation in response to ADP, platelet activating factor (PAF) and collagen, along with thromboxane B2 (TXB2) production during collagen induced aggregation, plasma TXB2 and plasma levels of lyso-PAF, in 38 subjects with and without ischaemic heart disease (12 with acute myocardial infarction, 9 with prolonged ischaemic chest pain without infarction and 17 normals). Lyso-PAF was measured, after in vitro acetylation to active PAF, by bioassay using 14C-serotonin labelled rabbit platelets. TXB2 was measured by radioimmunoassay. Plasma TXB2 was elevated at presentation only in patients with myocardial infarction (p less than 0.01). While impedance aggregation was similar in the three groups, aggregation to collagen resulted in greater release of TXB2 in subjects with myocardial infarction (p less than 0.01), an abnormality persisting 2-4 months later. Plasma lyso-PAF levels were significantly depressed throughout the first week in subjects with infarction (p less than 0.002), but after 2 to 4 months the level was greater than in normal subjects (p less than 0.001), changes presently unexplained. It is possible that the disorder of platelet function preceded and predisposed to coronary thrombosis. The findings strengthen the grounds for aspirin therapy in acute myocardial infarction.

Time dependence of whole blood aggregation in response to platelet activating factor (PAF)

The aggregation/adhesion response to platelet activating factor (PAF) was studied in diluted whole blood by impedance aggregometry. The extent of aggregation varied directly with the interval between blood sampling and aggregation measurement over the first 30 minutes from sampling, then remained stable for the next 60 minutes of observation. This is an effect opposite to that described for aggregation to PAF in platelet rich plasma which, however, cannot be studied soon after sampling. Time dependence of aggregation is important and comparative measurements should be made during the period of stable aggregability.

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.