title: Hyperosmolarity stimulates prostaglandin synthesis and cyclooxygenase-2 expression in activated rat liver macrophages.
abstract: The effect of aniso-osmotic exposure on the level of inducible cyclooxygenase (Cox-2) and on prostanoid synthesis was studied in cultured rat liver macrophages (Kupffer cells). In lipopolysaccharide (LPS)- or phorbol 12-myristate 13-acetate-stimulated Kupffer cells, hyperosmotic (355 mosmol/l) exposure, due to addition of NaCl or impermeant sugars, markedly increased prostaglandin (PG) E2, D2 and thromboxane B2 synthesis in a time- and osmolarity-dependent manner. Increased prostanoid production was observed about 8 h after exposure to LPS in hyperosmotic medium compared to Kupffer cells treated with LPS under normotonic (305 mosmol/l) conditions. A similar stimulatory effect of hyperosmolarity on PGE2 production was also seen when arachidonate was added exogenously. Hyperosmotic stimulation of PGE2 production was accompanied by a strong induction of Cox-2 mRNA levels and an increase in immunoreactive Cox-2, whereas the levels of immunoreactive phospholipase A2 and cyclooxygenase-1 did not change significantly. Dexamethasone, indomethacin and the selective Cox-2 inhibitor, NS-398, abolished the hypertonicity-induced stimulation of PGE2 formation; dexamethasone also prevented the increase in Cox-2 mRNA and protein. The increase of immunoreactive Cox-2 lasted for about 24 h and was also blocked by actinomycin D or cycloheximide, but not by brefeldin A. Tunicamycin or treatment with endoglucosidase H reduced the molecular mass of hypertonicity-induced Cox-2 by 5 kDa. Tunicamycin treatment also suppressed the hypertonicity-induced stimulation of PGE2 production. The hyperosmolarity/LPS-induced stimulation of prostaglandin formation was partly sensitive to protein kinase C inhibition but was not accompanied by an increase in the cytosolic free Ca2+ concentration. The data suggest that osmolarity may be a critical factor in the regulation of Cox-2 expression and prostanoid production in activated rat liver macrophages.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015232:Dinoprostone / Q000096:biosynthesis / Q000378:metabolism; D004790:Enzyme Induction; D005786:Gene Expression Regulation / Q000235:genetics; D006596:Hexosaminidases / Q000494:pharmacology; D007728:Kupffer Cells / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008262:Macrophage Activation; D008297:Male; D009994:Osmolar Concentration; D010120:Oxytocics / Q000494:pharmacology; D011448:Prostaglandin Antagonists / Q000494:pharmacology; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis* / Q000235:genetics; D011453:Prostaglandins / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013931:Thromboxanes / Q000096:biosynthesis
chemical_list: D008070:Lipopolysaccharides; D010120:Oxytocics; D011448:Prostaglandin Antagonists; D011453:Prostaglandins; D012333:RNA, Messenger; D013931:Thromboxanes; D016718:Arachidonic Acid; D000255:Adenosine Triphosphate; D011451:Prostaglandin-Endoperoxide Synthases; D006596:Hexosaminidases; D015232:Dinoprostone; D002118:Calcium