Effect of pH on Platelet Aggregation and Leakage of β-Thromboglobulin from Platelets

Abstract

Experiments were carried out to determine whether there is a relationship between leakage of β-thromboglobulin (BTG)from platelets and changes in response to ADP occurring during storage or changes in pH. Blood or platelet rich plasma (PRP) collected in 0.1M citrate was incubated at 37°C and plasma BTG estimated by radioimmunoassay; further leakage of BTG was effectively prevented by adding PGE1 and cooling to 0-4°C.Plasma BTG concentration was 21ng/ml at venesection and 95ng/ml 60 minutes later when pH of PRP or whole blood was maintained at 7.35-7.50 by a 5% CO2 atmosphere. Further leakage was slight, plasma BTG being 123ng/ml at 120 minutes, but when pH was allowed to drift to 8.6 at 120 minutes after venesection plasma BTG was 325ng/ml (3.5% of total platelet BTG) and this was accompanied by liberation of 8.6% of H3'-serotonin from the platelets. Similar results were obtained when pH of whole blood was allowed to drift to 7.7. At pH 7.7-8.0 platelet aggregation was consistently enhanced.The experiments demonstrated leakage of BTG from platelets within 30 minutes of venesection and before deterioration of response to ADP. Further leakage of BTG and serotonin was induced by a shift in plasma pH and may be due to a pH related stimulus causing both changes in sensitivity to ADP and release of granule contents. Initial leakage after venesection may reflect small unavoidable changes in pH.