Inhibition of prostaglandin D2 clearance in rat hepatocytes by the thromboxane receptor antagonists daltroban and ifetroban and the thromboxane synthase inhibitor furegrelate

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Prostanoids, i.e. prostaglandins and thromboxane, regulate liver-specific functions both in homeostasis and during defense reactions. For example, prostanoids are released from Kupffer cells, the resident liver macrophages, in response to the inflammatory mediator anaphylatoxin C5a, and mediate an enhanced glucose output from hepatocytes as energy supply. In perfused rat livers, the thromboxane receptor antagonist daltroban enhanced C5a-induced prostanoid overflow and reduced glucose output. It was the aim of this study to elucidate whether daltroban interfered with prostanoid release from Kupffer cells or prostanoid clearance by hepatocytes, and/or whether it directly influenced prostanoid-dependent glucose metabolism in these cells. In perfused rat livers, daltroban enhanced prostaglandin (PG)D2 overflow not only after infusion of C5a (15-fold), but also after PGD2 (10-fold). Neither daltroban nor another receptor antagonist, ifetroban, or the thromboxane synthase inhibitor furegrelate enhanced prostanoid release from Kupffer cells. In contrast, all inhibitors reduced clearance, i.e. uptake and degradation, of PGD2 by hepatocytes: within 5 min uptake of 1 nmol/L PGD2 was reduced from 43±5 fmol (controls) to 22±6 fmol (daltroban), 24±6 fmol (ifetroban) and 21±6 fmol (furegrelate). PGD2 in the medium was reduced to 39±7% in the controls, but remained at 93±9%, 93±11% and 60±3% in the presence of the inhibitors. PGD2-dependent glucose output in the perfused liver or activation of glycogen phosphorylase in isolated hepatocytes remained unaffected by daltroban. These data clearly demonstrate that the thromboxane-inhibitors reduced PGD2 clearance by hepatocytes, presumably by inhibition of prostanoid transport into the cells. In contrast, they did not interefere with PGD2-dependent glucose metabolism, suggesting an independent mechanism for the inhibition of glucose output from the liver.

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