Thromboxane A2 and Prostacyclin Release in Bleeding Time Blood during Primary Haemostasis in Healthy Individuals

ABSTRACT 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 F_1α (6-keto-PGF_1α) and thromboxane B₂ (TXB₂), both of which were measured in venous plasma as well as in serum (clotted at 37°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 < 1 ng/ml and in serum 275 ng/ml. The levels of immunoreactive 6-keto-PGF_1α 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.