Incorporation and metabolism of [14C]-arachidonic acid in guinea-pig lungs

1 Following infusion of [¹⁴C]-arachidonic acid into guinea-pig isolated lungs more than half the administered radioactivity was retained by the lung.

2 The majority of the retained radioactivity was present in the phospholipid fraction with lesser amounts in the neutral lipid and free fatty acid fractions. When fatty acid methyl esters of the phospholipid fraction were prepared, 80% of the radioactivity co-chromatographed with methyl arachidonate.

3 Transformation to cyclo-oxygenase products and subsequent emergence in lung effluent accounted for approximately 20% of infused radioactivity.

4 After pretreatment of lungs with [¹⁴C]-arachidonic acid, stimulation of arachidonic acid metabolism with injections of partially purified slow-reacting substance of anaphylaxis (SRS-A), bradykinin or antigen challenge released rabbit aorta contracting substance (RCS) and prostaglandin-like substances (PGLS) but little radioactivity. Furthermore, repeated injections of SRS-A or bradykinin released similar amounts of RCS and PGLS but diminishing amounts of radioactivity.

5 These data indicated that exogenous arachidonic acid was taken up by the lung and incorporated into phospholipids. However, this newly incorporated arachidonic acid had not equilibrated with the pool activated by SRS-A, bradykinin and antigen challenge for conversion to cyclo-oxygenase products.