Agonist-stimulated glycerophospholipid acyl turnover in alveolar macrophages

The inflammatory compounds β-glucan, a particulate agonist, and tannin, a soluble agonist, are present in cotton dust and, when inhaled, cause massive arachidonic acid release from alveolar macrophages. Earlier work had shown that these agonists exhibit different effects on arachidonate liberation and release, and that only tannin inhibits the uptake and incorporation of exogenous arachidonic acid, suggesting inhibition of reacylation. Here we have used the time-dependent incorporation of ¹⁸O from H₂¹⁸O-containing media into glycerophospholipid acyl groups as an indicator of acyl turnover in resting and agonist-treated rabbit alveolar macrophages. Highest turnover rates were seen in phosphatidylinositol (∼30% per hour) and in choline phospholipids (10–20% per hour). Both β-glucan and tannin stimulated acyl turnover, especially arachidonic acid turnover, in these and other lipid classes by a factor of 2 or more. We conclude that neither agonist promotes arachidonic acid accumulation in and release from alveolar macrophages by inhibiting reacylation.