Systemic and regional hemodynamic effects of cyclo-oxygenase and thromboxane synthetase inhibition in normal and hyperdynamic endotoxemic rabbits.

We tested the hypothesis that prostaglandins (PGs) and thromboxane (Tx) A2 are important mediators of the hemodynamic derangements occurring in a rabbit model of hyperdynamic endotoxicosis. Rabbits were injected with either normal saline (NS) or Escherichia coli lipopolysaccharide (LPS; 1-3 micrograms/kg) and studied 6 hr later. Cardiac index (CI) and regional blood flow were determined using thermodilution and radioactive microspheres, respectively. Systemic and regional hemodynamics were determined before and 40 min after administering indomethacin (cyclo-oxygenase inhibitor; 5 mg/kg), UK38485 (Tx synthetase inhibitor; 10 mg/kg), or NS. LPS increased CI (P = .0024) and decreased mean arterial pressure (P = .0031) and systemic vascular resistance index (P = .0001). LPS increased flow to the heart and small intestine and decreased flow to the hepatic artery and pancreas. The systemic and regional hemodynamic effects of indomethacin were similar in NS- and LPS-treated rabbits. UK38485 decreased perfusion of skeletal muscle and diaphragm in both endotoxemic and control animals. This agent increased splenic perfusion only in NS-treated rabbits. Plasma levels of 6-keto PGF1 alpha (PGI2 metabolite) were typically undetectable in both NS- and LPS-treated rabbits. These data do not support the hypothesis that PG's or TxA2 are major determinants of the hemodynamic perturbations that occur in this endotoxicosis model.