ABSTRACT
We show that lipopolysaccharide-free actetylated low-density lipoprotein (LDL), but not native LDL, stimulates tumor-necrosis factor-alpha (TNF-alpha) secretion by rat peritoneal macrophages and the signal-transduction pathways involved. The role of the scavenger receptor (SR) in this response was suggested by the absence of an effect induced by native LDL, signal coupling involving pertussis-toxin-dependent guanine-nucleotide-binding regulatory (G) protein, and the complete inhibition of this response by SR ligands [poly(I) and dextran sulfate]. Acetylated LDL induces rapid Ca2+ release from inositol-phosphate-sensitive Ca2+ stores mediated by pertussis-sensitive G proteins and a sustained Ca2+ rise mediated by Ca2+ influx and by Ca2+ release from ryanodine-sensitive Ca2+ stores. Acetylated LDL-induced Ca2+ influx and TNF-alpha production were abolished by inhibitors of phospholipase C (U73122) and phospholipase A2 (bromophenacyl bromide), but were not affected by an inhibitor of protein kinase C (calphostine C). Therefore, Ca2+ influx induced by acetylated LDL is dependent on Ca2+ store depletion. Arachidonate released by acetylated LDL acts as a second messenger to activate TNF-alpha secretion via Ca2+ influx. While the Ca2+ signal was not modified by an inhibitor of protein tyrosine kinases (PTK; herbimycin A), this inhibitor completely blocked TNF-alpha production, suggesting the involvement of PTK downstream of the Ca2+ signal. These results suggest that a sustained elevation of intracellular Ca2+, mediated through Ca2+ influx via the phospholipase-A2-dependent pathway, is essential for induction of TNF-alpha secretion. The type of SR class involved in these pathways remains to be identified.
Subject(s)
Lipoproteins, LDL/pharmacology , Macrophages, Peritoneal/drug effects , Macrophages, Peritoneal/metabolism , Membrane Proteins , Receptors, Lipoprotein , Tumor Necrosis Factor-alpha/biosynthesis , Animals , Arachidonic Acid/metabolism , Calcium/metabolism , Enzyme Inhibitors/pharmacology , In Vitro Techniques , Kinetics , Male , Models, Biological , Phospholipases A/antagonists & inhibitors , Phospholipases A2 , Protein Kinase C/antagonists & inhibitors , Protein-Tyrosine Kinases/antagonists & inhibitors , Rats , Rats, Sprague-Dawley , Receptors, Immunologic/agonists , Receptors, Immunologic/metabolism , Receptors, Scavenger , Scavenger Receptors, Class B , Second Messenger Systems , Signal Transduction/drug effects , Type C Phospholipases/antagonists & inhibitorsABSTRACT
The aim of our work was to evaluate the influence of native low density lipoproteins (LDL) and LDL chemically modified by acetylation (acLDL) on incorporation and release of arachidonic acid (AA) in rat peritoneal macrophages. Compared to a control group without treatment, 100 micrograms/ml of acLDL for 15 h considerably increased the incorporation of [3H]AA in cholesterol-ester (CE) of rat peritoneal macrophages and induced a decrease of 3H-labeled membrane phospholipids (PL). No effect was shown with LDL treatment. In the presence of acLDL, LS3251 (100 nM), an acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitor, inhibited the [3H]AA incorporation into CE in macrophages. [3H]AA-prelabeled macrophages cultured for 15 h with acLDL (compared to macrophages untreated or treated with LDL) showed an increase of labeled CE and a decrease of labeled PL and of cyclooxygenase and lipoxygenase eicosanoid production. After zymosan stimulation of macrophages prelabeled with [3H]AA and treated with or without LDL or acLDL, AA release and eicosanoid production increased in all groups of macrophages. The inhibition of eicosanoid production in foam cells does not seem to be linked to an inhibition of phospholipase but rather paralleled to an increase of the cholesterol [3H]arachidonate. A significant portion of cellular arachidonate released from phospholipids, in particular from phosphatidylcholine, could serve as a substrate to ACAT in this foam cell.
Subject(s)
Arachidonic Acid/metabolism , Arachidonic Acids , Cholesterol Esters/metabolism , Lipoproteins, LDL/pharmacology , Macrophages, Peritoneal/metabolism , Phospholipids/metabolism , Acetylation , Animals , Eicosanoids/metabolism , Enzyme Inhibitors/pharmacology , Lipoxygenase/metabolism , Macrophages, Peritoneal/ultrastructure , Male , Microscopy, Electron , Prostaglandin-Endoperoxide Synthases/metabolism , Rats , Rats, Sprague-Dawley , Sterol O-Acyltransferase/antagonists & inhibitorsABSTRACT
Nervous and hormonal controls of the gut system were studied in 42 hens using electromyography with transparietal electrodes. The results were analysed in relation with various biochemical parameters. The hormonal changes which occurred during sexual maturation and the ovulatory cycle induced directly the circadian organization of the motility of the gizzard and indirectly the motility of the intestinal tract. This resulted from variable metabolic requirements, the calcium being the most important element. An antagonism between gizzard and intestine motility was demonstrated. The pharmacological study confirmed the excitatory effect of the cholinergic system. For the adrenergic system, alpha receptors were predominant on the gizzard and beta receptors on the intestinal tract, especially in the distal part.