Cyclic-AMP inhibits neither A23187-stimulated [14C]-arachidonic acid release from prelabelled lipids nor phospholipase A2 activity in resident rat peritoneal macrophages.
8-Bromo cyclic AMP inhibited A23187-stimulated PGE2 production in adherent resident rat peritoneal macrophages by 50% when this was assessed by radioimmunoassay. In contrast, neither exogenous 8-bromo cyclic AMP nor elevation of endogenous cyclic AMP with cholera toxin inhibited 14C-arachidonic acid release or labelled prostaglandin formation by [1-14C]-arachidonic acid-prelabelled macrophages stimulated with either A23187 or melittin. Inhibition by cyclic AMP appears to be confined to PGE2 originating from a pool of endogenous phosphoglyceride that does not readily exchange with isotopically-labelled arachidonic acid. Phospholipase A2 activity, assessed as calcium-dependent [1-14C]-arachidonic acid release from exogenous 1-stearoyl, 2-[1-14C]-arachidonyl phosphatidyl choline at pH 8.6, was activated by melittin but not by A23187 in 1000 x g supernates from sonicated cells. Neither melittin nor calcium activation of phospholipase A2 was inhibited by preincubation of the cells prior to breakage with 8-bromo-cyclic AMP, nor by inclusion of either 8-bromo cyclic AMP or the catalytic subunit of cyclic AMP-dependent kinase in the assay. The results are inconsistent with the hypothesis that inhibition of A23187-stimulated PGE2 production by cyclic AMP in peritoneal macrophages is due to inhibition of a calcium-stimulated phospholipase A2.
Weidemann
M J
MJ
Department of Biochemistry, Faculty of Science, Australian National University, Canberra.
Arulthilakan
J J
JJ
Hunt
N H
NH
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology*; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D015232:Dinoprostone / Q000096:biosynthesis; D050356:Lipid Metabolism; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D008555:Melitten / Q000494:pharmacology; D010529:Peritoneal Cavity / Q000166:cytology; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D011460:Prostaglandins F / Q000096:biosynthesis; D011863:Radioimmunoassay; D051381:Rats
D001095:Arachidonic Acids; D011460:Prostaglandins F; D008555:Melitten; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000001:Calcimycin; D002772:Cholera Toxin; D000242:Cyclic AMP; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D015232:Dinoprostone