Platelet factor 4 (PF-4). A study on methodology and physiology.

Abstract

A modification of the serial heparin dilution technique for platelet factor 4 assay (Harada & Zucker 1971) is presented, using ox plasma as a source of fibrinogen and heparin cofactor. Activities are expressed in units heparin being neutralized per ml PPP or per platelet. Strong centrifugation forces induced release of PF‐4 from the platelets. Sample pH slightly influenced the results. The activity was considerably reduced upon heating to 56° C. Normal values are presented. Each individual seemed to have fairly constant activities. Following a fatty meal, fasting or heavy physical exercise, there was a significant increase in PPP heparin neutralizing activity (HNA). Reduction in activity per platelet was significant only after exercise. These findings are suggestive of in vivo release. Pregnancy did not change the activity levels, whereas women taking oral contraceptives had a considerably higher platelet activity than a reference group. Their PPP activities were similar. The results indicate that assays of heparin neutralizing activity in PPP and per platelet may be an index of platelet release, and thus be useful as a platelet function test in clinical medicine.