Platelet aggregability to platelet activating factor at rest and after exercise in patients with coronary artery disease

The platelet response to the aggregatory effect of platelet-activating factor (PAF) in relation to blood PAF levels, serum PAF-acetylhydrolase (PAF-AH) activity and to their lipidaemic profile, was studied in 44 patients with coronary artery disease undergoing exercise tests. The PAF EC50 values in 21 patients with positive exercise test results were found to be significantly decreased at rest compared with 21 normal subjects (12.6 +/- 3.9 nM and 24.9 +/- 11.7 nM respectively) (P<0.0001). Moreover, the maximal percentage of aggregation to 50 nM PAF was found to be significantly increased (20.0 +/- 4.3% vs 13.5 +/- 3.6%, respectively) (P<0.0001). By contrast, the PAF EC50 values and the maximal percentage of aggregation in 23 patients with negative exercise test results were not statistically significantly different from the control group (25.2 +/- 11.4 nM and 14.1 +/- 4.7%, respectively). At the end of exercise, the PAF EC50 values and the maximal percentage of aggregation did not change in any group, and there were no significant differences in the whole-blood PAF levels either at rest or at the end of exercise. In patients with positive exercise test results, the PAF-AH activity at rest was significantly higher compared with the control group (37.2 +/- 8.0 nmol.ml(-1).min(-1) vs 32.4 nmol.ml(-1).min(-1), (P<0.03), whereas the enzyme activity did not differ in patients with negative exercise test results compared to controls (33.6 +/- 6.1 nmol.ml(-1).min(-1)). There was no change in PAF-AH activity during exercise in any group. The enzyme activity was positively correlated to the serum total and low density lipoprotein (LDL) cholesterol levels in the control group and in patients with negative exercise test results, whereas no correlation was found between PAF-AH activity and total or LDL cholesterol levels in patients with positive exercise test results.

Effect of preload and afterload on ventricular arrhythmogenesis

To examine whether it is an increase in preload or afterload that may cause ventricular arrhythmias, the ventricles of 13 anesthetized open-chest dogs were bandaged. Next, metaraminol, an almost pure alpha stimulator, was given, followed by removal of the bandage. The ventricles were then sucked in a plastic cup, which was finally removed. The systolic and diastolic ventricular pressures were measured, and the presence of arrhythmias (ventricular ectopic beats or ventricular tachycardia) was observed. Banding the ventricles caused a significant diminution of systolic pressure (-42 +/- 38.0 mmHg; mean +/- SD) and a rise in diastolic pressure (+3.5 +/- 3.7), starting from control values of 126 +/- 36/6.5 +/- 3.0, but no arrhythmia. Metaraminol raised both pressures (+122 +/- 58 and +9.0 +/- 10.3) and caused ventricular arrhythmias in 6 of 13 experiments. Removing the bandage further increased the systolic pressure (+45 +/- 42) and reduced the diastolic pressure (-7.2 +/- 10.3), but made the arrhythmia worse in 10 of 13 experiments. Suction reduced both pressures (-166 +/- 96 and -5.4 +/- 14) and stopped all arrhythmias. Removing the cup increased both pressures (+133 +/- 68 and +15.5 +/- 15.3, respectively) and worsened the arrhythmia in seven of eight experiments. In general, deterioration of ventricular arrhythmias was observed in 23 of 25 maneuvers with either an increase or no change in systolic pressure, but in none of the maneuvers was there a decrease (P < .0001) in systolic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of PAF-acetylhydrolase activity in human plasma low-density lipoprotein subfractions

The distribution of PAF-acetylhydrolase (PAF-AH) activity in 3 LDL subfractions prepared by density gradient ultracentrifugation as well as the rate of phosphatidylcholine (PC) hydrolysis during oxidation was studied. PAF-AH activity, measured before oxidation, was much higher in LDL3 subfraction (28.4 +/- 8.6 nmol/mg per min) comparing to LDL2 (14.1 +/- 5.8 nmol/mg per min), and to LDL1, 8.7 +/- 3.7 nmol/mg per min. During oxidation, the enzyme activity was continuously decreased and this phenomenon was more pronounced in LDL1. PC hydrolysis was studied measuring the lyso-PC production expressed as lyso-PC/Sph molar ratio. Before oxidation, the lyso-PC/Sph molar ratio, did not differ significantly among the LDL subfractions, whereas, 4 h after the onset of oxidation, it was significantly higher in LDL2 and LDL3 subfractions (0.42 +/- 0.12 and 0.45 +/- 0.10, respectively), comparing to LDL1 (0.29 +/- 0.06). Our results show that the distribution of PAF-AH activity in LDL subfractions is heterogeneous (mainly distributed in LDL2 and LDL3 subfractions) and it is positively correlated with higher lyso-PC production in those subfractions during oxidation. The contribution of this phenomenon to the enhanced susceptibility to oxidation as well as to the higher atherogenicity of the dense LDL subfractions is under investigation.