IDENTIFICATION OF THE THROMBOXANE A(2) RECEPTOR IN HEPATIC SINUSOIDALENDOTHELIAL-CELLS AND ITS ROLE IN ENDOTOXIN-INDUCED LIVER-INJURY IN RATS

The presence of the thromboxane A(2) receptor in sinusoidal endothelia l cells was investigated and its pathogenic role in endotoxin-induced liver injury examined. The receptor was measured with a binding assay using a specific thromboxane A(2) receptor antagonist, [H-3]S-145. Sca tchard analysis of the binding indicated the presence of a single clas s of high-affinity binding sites with a dissociation constant of 5.00 +/- 0.96 nmol/L, a maximal binding of 22.85 +/- 2.71 fmol/10(6) cells and 13.80 +/- 1.60 x 10(3) binding sites per cell. The addition of a c yclooxygenase inhibitor, indomethacin, during the cell preparation inc reased the maximal binding value and the number of binding sites of 37 .34 +- 3.01 and 22.50 +/- 1.80 x 10(3) sites/cell, respectively. The b inding was displaced by various thromboxane A(2) analogs such as ONO-3 708 and STA(2) but was not effectively competed for by other prostagla ndins. Endotoxin injection reduced dissociation constant, maximal bind ing and the number of binding sites in sinusoidal endothelial cells to 3.49 +/- 0.87 nmol/L, 6.03 +/- 0.64 fmol/10(6) cells and 3.65 +/- 0.3 9 x 10(3) sites/cell, respectively. A cyclooxygenase inhibitor and a K upffer cell inhibitor added before endotoxin treatment significantly p revented the reduction in the number of thromboxane A(2) receptors. It is possible that these effects were due to a reduction in the agonist -induced internalization of the thromboxane A(2) receptor brought abou t by the prevention of thromboxane A(2) production. Preadministration of both a cyclooxygenase inhibitor and a thromboxane A(2) receptor ant agonist attenuated the degree of endotoxin-induced liver injury. These findings indicated that the thromboxane A(2)-thromboxane A(2) recepto r system in the hepatic sinusoids plays a significant role in the path ogenesis of endotoxin-dependent liver damage.