– 1a,1b-dihomo Prostaglandin E2 (PGE2) is a rare polyunsaturated fatty acid initially identified in sheep vesicular gland microsome extracts containing COX and incubated with adrenic acid. It has also been detected in conditioned media of RAW 264.7 macrophages stimulated with endotoxin and arachidonic acid. This compound is believed to be produced by the elongation of AA to adrenic acid, followed by sequential metabolism by COX and PGE synthase.