Thromboxane A2 and prostacyclin release in bleeding time blood during primary haemostasis in healthy individuals

It is generally believed that prostacyclin (PGI2) generation is greatly stimulated when blood vessels are injured, even by minor trauma, such as venepuncture. The Simplate technique for measuring skin bleeding time was adapted to quantify by radioimmunoassay PGI2 and thromboxane A2 (TXA2) in the emerging blood, as the stable degradation products 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 (TXB2), both of which were measured in venous plasma as well as in serum (clotted at 37 degrees C for 1 h). During bleeding, when platelets aggregate to occlude the injured vessels, the median TXB2 level in the emerging bleeding time blood was 1.7 ng/ml. The median TXB2 level in plasma was less than 1 ng/ml and in serum 275 ng/ml. The levels of immunoreactive 6-keto-PGF1 alpha were always below determination limit in bleeding time blood (0.2 ng/ml) and in plasma (0.1 ng/ml), whereas in serum the levels ranged between 0.26 and 0.47 ng/ml. The fact that enhanced PGI2 production in primary haemostasis in skin incisions could not be demonstrated calls for further investigations of possible PGI2 production with more sensitive assays or in injured large vessels.