Effect of serum on the metabolism of exogenous arachidonic acid by phagocytic cells of the mouse thymic reticulum.

Phagocytic cells derived from the mouse thymic reticulum (P-TR) were used to study the effect of serum on the metabolism of arachidonic acid (AA). After labeling with (14C)-AA in the presence of 10% serum, we failed to detect in the culture medium the presence of significant amounts of radiolabeled prostaglandins. In contrast, when the labeling period was carried out in serum-free medium, we observed the secretion of both cyclooxygenase and lipoxygenase derivatives. In addition, the pattern of arachidonate incorporation into cell lipids was different in the two culture conditions. In the presence of serum, the great majority of the radioactivity was found associated with phospholipids, whereas in serum-free medium, almost 50% of the incorporated fatty acid was associated with triglycerides. Since serum albumin is known to play a major role in the control of fatty acid uptake, we have studied the effect of the addition of 2% BSA to cells prelabeled in the absence of serum. This treatment switches the patterns of metabolite release and lipid labeling towards those of serum-treated cells. In addition, we showed that the effects of glucocorticoids on AA release differ markedly according to the composition of the culture medium.