The release of thromboxane A₂ and prostacyclin following experimental acute pulmonary embolism

The contributions of thromboxane A₂ (TXA₂) and prostacyclin (PGI₂) to the effects of acute pulmonary embolism were evaluated in 18 open-chest rabbits. All rabbits received autologous whole-blood-clot embolus (.4 cc) by way of a catheter in the right ventricle. Pulmonary artery (PA) and left atrial (LA) pressures, and aortic flow (AOQ) were recorded. The stable metabolites of TXA₂ (TXB2) and PGI₂ (6-Keto PGF₁ ) were assayed by radioimmunoassay at pre- and postembolization periods (+5, +10, +20, +30, and +40 minutes). Significant elevations of pulmonary vascular resistance (PVR) (normalized), PA pressure, and reduction of AOQ were noted comparing pre-embolus to +5 minute time intervals.A negative correlation was reached between PGI₂ and AOQ at +40 minutes (p <.05). Five of the 13 rabbits died prematurely. At +5 minutes these 5 rabbits had higher PVR (p < 001) and lower AOQ (p (.01) than their living counterparts. At +10 minutes AOQ was still significantly lower (p < 005) and TXB₂ was higher (p < 05) in the premature death group. We conclude that TXB2 is significantly but transiently elevated early following acute pulmonary embolism and may contribute to mortality. In contrast PGI2 does not appear to play an immediate role in the hemodynamic events following embolization but does rise to significant levels later in the course possibly in an attempt to compensate for reduced flow.