Oxidized derivatives of linoleic acid have the potential to alter steroidogenesis. One such derivative is 12,13-epoxy-9- keto-10-(trans)-octadecenoic acid (EKODE). To evaluate the effect of EKODE on corticosterone production, dispersed rat zona fasciculata/reticularis (subcapsular) cells were incubated for 2 h with EKODE alone or together with rat ACTH (0, 0.2, or 2.0 ng/ml). In the absence of ACTH, EKODE (26 microM) increased corticosterone production from 5.3 +/- 2.3 to 14.7 +/- 5.0 ng. 10(6) cells. h(-1). The stimulatory effect of ACTH was increased threefold in the presence of EKODE (26.0 microM). Cholesterol transport/P-450scc activity was assessed by measuring basal and cAMP-stimulated pregnenolone production in the presence of cyanoketone (1.1 microM). EKODE (13.1 and 26.0 microM) significantly increased basal and cAMP-stimulated (0.1 mM) pregnenolone production. In contrast, EKODE decreased the effect of 1.0 mM cAMP. EKODE had no effect on early or late-pathway activity in isolated mitochondria. We conclude that EKODE stimulates corticosterone biosynthesis and amplifies the effect of ACTH. Increased levels of fatty acid metabolites may be involved in the increased glucocorticoid production observed in obese humans.