Abstract
TNF-alpha is a critical mediator of hepatic microcirculatory dysfunction during endotoxemia. The present study was to investigate the role of thromboxane A2 (TXA2) and the biological significance of thromboxane prostanoid (TP) receptor signaling in TNF-alpha-mediated hepatic microcirculatory dysfunction in male C57Bl/6 mice. The number of leukocytes adhering to the endothelial cells of the hepatic microvessels (the portal venules, sinusoids, and central venules) and the percentage of nonperfused sinusoids were determined using in vivo fluorescence microscopy. FR167653, an inhibitor of TNF-alpha, was administered 0 and 2 h after LPS injection. A TXA2 synthase inhibitor, OKY-046, was administered 30 min before TNF-alpha injection. Thromboxane prostanoid receptor knockout mice were used to investigate whether TNF-alpha-induced hepatic microcirculatory dysfunction is mediated by endogenously produced TXA2. FR167653 reduced LPS-induced leukocyte adhesion (50%-80%) and the percentage of nonperfused sinusoids (55%). The leukocyte adhesion was increased in the portal venules (8-fold), sinusoids (51-fold), and central venules (73-fold) in TNF-alpha-treated mice, accompanied with an increase in sinusoidal perfusion deficits (8-fold). Alanine aminotransferase levels rose as the adhesion of leukocytes increased. OKY-046 administration before TNF-alpha administration reduced leukocyte adhesion (41%-49% decrease) and sinusoid perfusion deficits (34% decrease). In TP receptor knockout mice, the number of adhering leukocytes, the percentage of nonperfused sinusoids, and alanine aminotransferase levels were lower (by 43%-56%, 41%, and 29%, respectively) than in wild-type counterparts. The results suggest that TP receptor signaling may promote hepatic microcirculatory dysfunction elicited by TNF-alpha. Blockade of TNF-alpha generation and TP receptor signaling may be a good strategy for managing endotoxin-induced hepatic injury.
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