DISCRETE PATHWAYS FOR ARACHIDONIC-ACID RELEASE FROM TANNIN VERSUS BETA-GLUCAN-STIMULATED RABBIT ALVEOLAR MACROPHAGES

Previously, we observed both tannin and beta-glucan to be agonists for arachidonic acid (AA) release from rabbit alveolar macrophages, Altho ugh tannin inhibited reincorporation of exogenous AA, beta-glucan had no apparent effect, suggesting separate signal transduction pathways l eading to elevated AA levels, In this study alveolar macrophages were pretreated with the tyrosine phosphatase inhibitor sodium orthovanadat e then stimulated with either condensed tannin or beta-glucan, Vanadat e exerted opposing effects on AA release, Furthermore, vanadate revers ed the ability of tannin to inhibit reacylation, Additional studies us ing the phospholipase A probe bis-BODIPY-C-11-PC indicated that althou gh the known phospholipase A(2) activators, calcium ionophore A23187, insoluble immune complexes, and beta-glucan, generated an increase in fluorescence consistent with phospholipase A activation, tannin had no effect, These findings suggest the increase in free AA resulting from stimulation of macrophages by either tannin or beta-glucan is produce d via two different mechanisms.