Activity of platelet-activating factor (PAF) acetylhydrolase in plasma was estimated in 35 patients with cerebral thrombosis, 18 with essential hypertension, and 34 healthy adults age-matched with two groups of patients. In all cerebrovascular patients more than 3 months had elapsed since their stroke. The assay measured the inhibition of PAF-induced platelet aggregation by the preincubation of a standard PAF solution with sample plasma. For this purpose, platelet aggregation induced by a PAF solution which had been preincubated with an equal amount of citrated plasma at 37°C for 15min was compared with that induced by a control PAF solution which had been preincubated with phosphate-buffered saline.
The average values of plasma PAF acetylhy-drolase activity in the cerebrovascular patients and the hypertensives were 4.18±3.08 and 1.71±0.27μg/ml, respectively. These values were significantly higher than the average value of plasma PAF acetylhydrolase activity in the control group: 1.51±0.51μg/ml. In each of three groups, plasma PAF acetylhydrolase activity correlated positively with the level of serum LDL-cholesterol, reflecting the complex formation of this enzyme with plasma lipoproteins, mainly with LDL. Serum LDL-cholesterol level in the cerebrovascular patients was higher than that in the control, which may account, in part, for the higher-than-normal plasma PAF acetylhydrolase activity in the patients. However, relative activity of PAF acetylhydrolase to LDL-cholesterol level was found to be higher in both patient groups as compared to the control. This result may suggest that patients' LDL contains higher activity of the enzyme than that of healthy subjects, and such a fact could be considered as one of the qualitative alterations of lipoproteins in these patients.