Increased platelet thromboxane A₂/prostaglandin H2 receptors in patients with pregnancy induced hypertension

Pregnancy induced hypertension (PIH) is associated with a variety of disturbances in the hemostatic system including alterations in platelet function, thrombocytopenia (1), and an increase in platelet turnover (2,3). The density of platelet Thromboxane A₂ (TXA₂)/Prostaglandin H2 (PGH2) receptors was determined in patients with PIH and normal pregnant women, using [¹²⁵I]-PTA-OH, a TXA₂/PGH₂ receptor antagonist. The number of platelet TXA₂/PGH₂ receptors significantly increased (p<0.008) from 1734±370 sites/platelet (n=8) in normal pregnant women to 3703±846 sites/platelet (n=9) in patients with severe PIH. The sensitivity of platelets to the TXA₂ mimetic U46619 was significantly (p<0.0005) increased in platelets obtained from severe PIH patients (EC₅₀=150±10nM, n=3) compared to controls (EC₅₀=290±60nM, n=5). These results indicate that an increased number of TXA₂/PGH₂ receptors as well as increased sensitivity to TXA₂/PGH₂ mimetics occurs in PIH. Collectively, these results provide further support for the notion that TXA2 and its receptor may play an important role in the pathophysiology of PIH.