LPS exacerbates endothelin-1 induced activation of cytosolic phospholipase A2 and thromboxane A2 production from Kupffer cells of the prefibrotic rat liver

Background/Aims Thromboxane A 2 (TXA 2 ) has been suggested to play a significant role in the development of portal hypertension in fibrosis, and Kupffer cell (KC) derived TXA 2 has been shown to mediate the hyperresponsiveness of the portal circulation to the vasoconstrictive actions of endothelin-1 (ET-1) during endotoxemia. The aim of this study was to determine whether the double stresses of prefibrotic changes and endotoxemia additively activate KC to increase release of TXA 2 in response to ET-1, resulting in elevated portal resistance. Methods One week Bile duct ligation (BDL) rats and sham-operated controls were subjected to isolated liver perfusions following LPS or saline for 6h. In a separate experiment, KC were isolated from BDL or sham rats and incubated with LPS or saline for 6h before the ET-1 treatment. Results The double stresses of early fibrosis and LPS resulted in a greater sustained increase in portal pressure in response to ET-1 in BDL rats, and this increase correlated well with the much enhanced release of TXA 2 in the perfusate. Media from the cultured KC showed significantly greater TXA 2 release in response to ET-1 in BDL group than those in sham group, and LPS exacerbated this effect. Protein levels of cytosolic phospholipase A 2 (cPLA 2 ), cyclooxygenase-2, and thromboxane synthase were also significantly elevated in KC from BDL rats. ET-1 produced a marked increase in cPLA 2 activation as measured by the phosphorylation of cPLA 2 in KC of both BDL and sham groups. LPS greatly exacerbated the activation of cPLA 2 . Conclusions The data suggest that the double stresses additively activate KC with an upregulation of the key enzymes in the TXA 2 biosynthesis and release increased amount of TXA 2 via the augmented activation of cPLA 2 in response to ET-1, which leads to the increased portal resistance and ultimately hepatic microcirculatory dysfunction.