PLATELET THROMBOXANE-A(2) RECEPTOR NUMBER AND FUNCTION IN NORMAL AND HYPERTENSIVE PREGNANCY

PROBLEM: Our study evaluated the number and function of platelets for thromboxane A2/prostaglandin H-2 (TxA2/PGH2) and the platelet response to TxA2 receptor agonists in normal and hypertensive pregnancy. In addition, correlations between platelet membrane lipid composition and TxA, receptor number and function were evaluated. METHODS: Ten normotensive healthy pregnant women (GC), 10 hypertensive pregnant women (PIH), and 10 normotensive nonpregnant healthy women (C) were examined. Radioligand binding and aggregation studies were performed. Lipid composition of platelet membrane was assessed as cholesterol to phospholipids ratio (CH/PL) and normalized to protein content. RESULTS: TxA2/PGH2 receptor binding sites and affinity did not differ among the groups. An enhanced response to TxA2 receptor agonist U 46619 in GC and in PIH compared to C was observed, while platelet response to thrombin was not different among the groups. CH/PL was altered in PIH respect to GC and C. No significant correlation was found between CH/PL and number and function of platelet TxA2 receptors in PIH. CONCLUSIONS: In PIH there is no alteration of number or function of TxA2 receptors on platelet membrane. However, the enhanced TxA2 production associated with the increased sensitivity of platelet to TxA2 in pregnancy may contribute to the microcirculatory thrombotic changes of PIH.