NEUTROPHIL RELEASE OF ARACHIDONIC-ACID, OXIDANTS, AND PROTEINASES - CAUSALLY RELATED OR INDEPENDENT

This investigation examined the concept that arachidonic acid (AA) ser ves as a second messenger in stimulation of the respiratory burst and degranulation of polymorphonuclear neutrophils (PMN). The main support for this idea is from observations that reagent AA added to cell susp ensions, stimulates the respiratory burst and degranulation and these events are blocked by PLA(2) inhibitors. We verified that exogenously- added AA stimulated release of O-2(-) myeloperoxidase (MPO), and lysoz yme (LZ), but this required amounts of AA which approximated the criti cal micellar concentration. This suggested that such administration of AA might act as an extracellular agonist, similar to particulate stim uli, rather than acting as a second messenger as might occur following mobilization of AA from cellular membranes. To investigate the role o f fatty acids released by hydrolysis of cellular phospholipids, exogen ously-added group I, II or III PLA(2)'s were used to mobilize fatty ac ids from cellular membranes. Mole quantities of cell-associated free f atty acids were measured by negative ion chemical ionization gas chrom atography mass spectrometry. AA mobilization in response to exogenous PLA(2) was dose-(0.1 to 10 U/ml PLA(2)) and time-dependent (peak at 1 to 2 min with a reduction by 4 min). Resting neutrophils contained <10 pmol free AA/10(7) PMN; the receptor-mediated agonist N-formyl-methio nyl-leucyl-phenylalanine (fMLP) alone did not increase these values. E xogenously-added PLA(2) generated large quantities of free AA in contr ol and fMLP-treated cells (426+/-122 and 2097+/-176 pmol/10(7) PMN, re spectively): however, this did not induce O-2(-), nor did it augment t he level of O-2(-) stimulated by fMLP. Also, PLA(2) caused no degranul ation and did not alter degranulation induced by fMLP. PLA(2) also did not alter O-2(-) or degranulation responses in primed PMN. The data i ndicate that mobilization of AA from cellular phospholipids neither st imulates nor modulates the respiratory burst or degranulation of PMN.