Butaprost, a structural analog of PGE2, is a selective agonist for the EP2 receptor subtype. EP2 receptors are expressed on human neutrophils and on respiratory, vascular, and uterine smooth muscle.{3178,1752} Butaprost binds with about 1/10 the affinity of PGE2 to the recombinant murine EP2 receptor, and does not bind appreciably to any of the other murine EP receptors or DP, TP, FP, or IP receptors.{6640} The EC50 for the stimulation of cAMP by butaprost in COS cells transfected with the human EP2 receptor is about 5 μM, while the EC50 for PGE2 in this assay is about 43 nM.{3178} Butaprost has frequently been used to pharmacologically define the EP receptor expression profile of various human and animal tissues and cells.{3317}