Rapid Increase in the Leukotriene B4 Concentration of Cultured Rat Hepatocytes by Heparin

Abstract

Heparin has various actions in animal tissues, but the action mechanisms have not been fully elucidated. Here, we have investigated the stimulatory increase in the leukotriene (LT) B 4 content of rat hepatocytes induced by heparin. Heparin increased the LTB 4 content of the hepatocytes in a time-dependent manner up to 5 min; its maximal effect was three-fold higher than the basal level of LTB 4 . When tyrosine kinase (TK) activity in the membrane-containing preparation of the hepatocytes was suppressed, the stimulatory increase in LTB 4 by heparin was markedly reduced. It was also observed that the heparin-stimulated increase in LTB 4 was reduced by various cytosolic phospholipase A 2 (PLA 2 ) inhibitors. These findings suggest that heparin stimulates a rapid increase in LTB 4 in rat hepatocytes, and that this increase is partly due to an action involving the membrane TK-and the cytosolic PLA 2 -sensitive pathways.

Involvement of Leukotriene Production in Release of Hepatic Lipase Activity Produced by Heparin from Rat Hepatocytes

“…39) Activation of the membrane TK by heparin in cultured rat hepatocytes was also reported to cause an increase in the intracellular LTB 4 contents. 15) In conclusion, our results suggest that the stimulatory release of HTGL activity by heparin is, in part, caused through a pathway involving an increase in PLA 2 activity and the resulting rise in LTs contents and an association with TK activity on the cell membrane. The hepatocytes were incubated for 60 min with or without heparin (2 U/ml) in the presence of various agents, as described in MATERIALS AND METHODS.…”

“…15) However, the involvement of PLA 2 and LTs in the heparin-stimulated release of HTGL activity is still unknown.…”

Prazosin Stimulates the Release of Hepatic Triacylglycerole Lipase Caused from Primary-culture Rat Hepatocytes

“…Determination of HTGL Activity --HTGL activity was determined by a method using glycerol tri[1-14 C]-oleate (1.2 µM; 2.5 kBq/ml) as a substrate. 17,18) The HTGL activity was expressed as pmol of free fatty acids (FFA) produced/min par 10 6 cells. Determination of Phospholipase C (PLC) Activity --PLC activity was determined by the method of Higashi et al 19) Briefly, the hepatocytes incubated with prazosin 0-100 µM over 30-min period, were homogenized in 20 mM Hepes-K buffer (pH 7.0) containing 1 mM dithiothreitol, 0.25 M sucrose, 1 mM EDTA and 0.7% cholateNa by Physcotron (a microhomogenizer; NS-310E model, Niti-on Co., Tokyo, Japan), and were centrifuged at 105000 × g for 60 min at 4 • C. The supernatant contained the cytosolic and membrane fractions.…”