Changes of prostacyclin and thromboxane synthesis in the course of mouse liver perfusion. Stimulated thromboxane A2 synthesis of freshly prepared isolated mouse hepatocytes

Prostaglandin-independent stimulation of interleukin-6 production by fibrinogen degradation product D in perfused murine liver

Bacterial endotoxin (LPS) and fibrinogen degradation product D (FDP-D) are both potent stimulators of interleukin-6 (IL-6) production in liver, however, there are differences in their metabolic effects. The aim of the present study was to compare the role of prostaglandins in the enhancement of IL-6 production by LPS or FDP-D in perfused mouse livers. Indomethacin inhibited the effect of LPS significantly but was ineffective in the case of FDP-D. Accordingly, production of prostaglandins D2 and E2 was not elevated following the addition of FDP-D, while their formation was increased several fold by LPS. At the same time interleukin-1 (IL-1) production in perfused liver rose markedly upon the addition of FDP-D. It is suggested that prostaglandins are not involved in the effects of FDP-D on the liver. The stimulatory effect of FDP-P on IL-6 production might be the consequence of elevated IL-1 levels.

Leukocyte and platelet depletion protects the liver from damage induced by cholestasis and ischemia-reperfusion in the dog

BACKGROUND

Ischemia-reperfusion injury has been studied in various organs. The effects of leukocyte and platelet depletion on cholestasis and ischemia-reperfusion-induced liver damage were evaluated in the dog liver.

METHODS

The left hepatic duct was ligated for 4 weeks to create a cholestatic lobe. An ischemic condition was produced for 60 min by stopping the peristaltic pump supplying blood to the liver. The metabolism of substances modulated in the liver during cholestasis and I-R was assessed in non-treated and in leukocyte- and platelet-depleted animals.

RESULTS

The extraction rate of insulin and indocyanine green decreased during cholestasis and ischemia-reperfusion. Cholestasis accelerated the release of thromboxane A2 but not prostaglandin I2 after ischemia-reperfusion. Ischemia-reperfusion accelerated the release of prostaglandin I2 and thromboxane A2 from the liver. Further, ischemia-reperfusion increased the ratio of thromboxane A2 to prostaglandin I2. Cholestasis promoted an increase in the level. Ischemia-reperfusion caused an increase in the lipid peroxide level, and no change in the alpha-tocopherol level. Ischemia-reperfusion caused an increase in the lipid peroxide level, a decrease in the alpha-tocopherol level, and no change in the glutathione level. Depletion of leukocytes and platelets reduced these changes during cholestasis and ischemia-reperfusion.

CONCLUSIONS

Depletion of leukocytes and platelets thus appears to protect liver function from cholestasis and ischemia-reperfusion injury by reducing peroxidation of lipids composing the cell membrane and the rate of thromboxane A2 prostaglandin I2, which predicts cellular damage, and by increasing the levels of alpha-tocopherol and glutathione, believed to be free radical scavengers.

The contribution of hepatocytes to prostaglandin synthesis in rat liver

The contribution of hepatocytes to liver prostaglandin (PG) synthesis Is not clear. We compared prostaglandin synthesis in homogenates of whole liver, freshly isolated hepatocytes, and mixed non-parenchymal cells from the same rat livers, and optimized the assay. Whole liver homogenates made 27.2 +/- 7.1 mg PGE2/mg protein/5 min (+/- SEM, n = 4 livers). Hepatocyte homogenates made 39 +/- 9% as much PGE2/mg protein as did the matched whole livers. Non-parenchymal cell homogenates made slightly more PGE2 than whole liver, but much more PGD2. Subsequent studies showed that fresh hepatocyte suspensions contain significant contamination with non-parenchymal cells. Homogenates from ricin-purified hepatocyte monolayers made at least half as much PGE2 as did conventional monolayers. However, taking cellular purity into account, hepatocytes must contain much less than a third of liver cyclooxygenase activity.

Enhancement of interleukin-6 production by fibrinogen degradation product D in human peripheral monocytes and perfused murine liver

The effect of fibrinogen degradation products D and E (FDP-D, FDP-E) on IL-6 production in perfused mouse livers and peripheral monocytes is studied. Similarly to bacterial endotoxin FDP-D is highly potent to augment the IL-6 production measured in perfused mouse livers, while FDP-E is not stimulatory. FDP-D but not FDP-E is able to stimulate the in vitro IL-6 production of human peripheral monocytes, as well. Plasmin alone is almost ineffective on IL-6 production both in perfused livers and monocytes. Our findings suggest a direct positive feedback circuit, among fibrinogen, FDP and IL-6.

Pathophysiology of dogs after 84% hepatectomy with emphasis on prostaglandin metabolites and the effect of a thromboxane A2 synthesis inhibitor and a prostaglandin I2 analog

The pathophysiological conditions following 84% hepatectomy were examined in terms of the changes in thromboxane A2 (TxA2) and prostaglandin I2 (PGI2) in a canine model. OKY-046, a TxA2 inhibitor, and OP-2507, a PGI2 analog, were administered to evaluate the possibility of extending hepatic resection. The 2-week survival rate following 84% hepatectomy significantly improved after the administration of OKY-046 and OP-2507, from 12.5% to 58.3% and 75.0%, respectively. Furthermore, OP-2507 significantly improved impaired hepatocyte and sinusoidal endothelial cell function after 84% hepatectomy, resulting in a satisfactory recovery to the preoperative levels. Within 24 h after 84% hepatectomy, the plasma levels of thromboxane B2 (TxB2) increased significantly, and the 6-keto-prostaglandin F1 alpha (6-KF) levels became slightly elevated. OKY-046 and OP-2507 decreased TxB2 and increased 6-KF in the plasma, resulting in the maintenance of sufficient blood flow in the portal vein and hepatic tissue and the mitigation of microcirculatory disorders. Moreover, the cytoprotective effects of the two drugs inhibited functional impairment of the residual liver. In conclusion, abnormal prostaglandin metabolites were produced after 84% hepatectomy, being involved in residual liver disorders. However, the administration of either an inhibitor of TxA2 synthesis or a PGI2 analog ameliorated the functional impairment of the residual liver, which suggests their potential value for extending the resectability of the liver from what is presently feasible.

Synthesis and degradation of eicosanoids in primary rat hepatocyte cultures

Arachidonic acid metabolites may play an important role in liver physiology, yet hepatocyte prostaglandin synthesis has not been characterized extensively. We used RIA to study production and clearance of several eicosanoids in confluent primary cultures of rat hepatocytes in serum-free, hormonally-defined medium. Under basal, unstimulated conditions 6-keto-PGF1 alpha (spontaneous breakdown product of prostacyclin) and 13,14-dihydro-15-keto-PGE (DHK-PGE, a metabolite of PGE) accumulated in the culture medium. Hepatocytes cleared 6-keto-PGF1 alpha, thromboxane B2, and DHK-PGE from the medium. Production of eicosanoids by primary cultures appeared resistant to indomethacin and several other cyclooxygenase inhibitors. This apparent resistance to indomethacin was not caused by rapid metabolism of indomethacin, by failure of the drug to enter hepatocytes, or by insensitivity of hepatocyte cyclooxygenase to the drug. Metabolism of PGE to DHK-PGE may be saturated under in vitro conditions. Hepatocytes can synthesize significant amounts of eicosanoids, although they are probably less active in this regard than are non-parenchymal cells.