MUCOSA-DEPENDENT MUSCARINIC LIBERATION OF PROSTAGLANDINS FROM RAT ISOLATED TRACHEA

1 The present study examined whether cholinoceptor stimulation modulates the release of arachidonic acid-derived mediators from rat isolated tracheae. 2 Tracheae were preincubated with [H-3]-arachidonic acid and the outflow of H-3-compounds was determined. Acetylcholine and the muscarinic agonist, carbachol but not nicotine, increased the rate of tritium outflow maximally by about 30%. The M(3) receptor-preferring antagonist p-fluorohexahydrosiladiphenidol was more effective than pirenzepine and methoctramine in antagonizing the effect of acetylcholine. 3 High performance liquid chromatography analysis (methanol gradient) of the released H-3-compounds showed that one peak, co-eluting with [C-14]-prostaglandin E(2) ([C-14]-PGE(2)) and [H-3]-PGD(2), was enhanced almost 10 fold following muscarinic receptor activation, whereas the outflow of [H-3]-arachidonic acid remained unaffected. 4 Using an acetonitril gradient separation it was shown that [H-3]-PGE(2), [H-3]-PGD(2) and [H-3]-PGF(2 alpha) are released spontaneously, but [H-3]-PGE(2) represented the major fraction of H-3-prostaglandins. Acetylcholine enhanced the release of all three H-3-prostaglandins, but the effect on PGE(2) was most pronounced and most consistent. 5 After removal of the mucosa the muscarinic effect of acetylcholine on total tritium and on that of the H-3-prostaglandins ([H-3]-PGE(2)/PGD(2) peak) was abolished. 6 Acetylcholine also enhanced the outflow of radioimmunologically determined PGE(2) in a mucosa-dependent manner. 7 After inhibition of cyclo-oxygenase by 3 mu M indomethacin, the outflow of H-3-prostaglandins was reduced to almost undetectable levels and acetylcholine evoked a marked release of [H-3]-arachidonic acid. The phospholipase A(2) inhibitor, quinacrine (up to 100 mu M) also blocked the effect of acetylcholine on the outflow of H-3-prostaglandins, but this was not followed by a compensatory increase in the outflow of [H-3]-arachidonic acid. 8 In conclusion, activation of muscarinic receptors which have characteristics of the M(3) subtype can evoke release of prostaglandins from the airway mucosa.