Butaprost is a structural analog of PGE2 with good selectivity for the EP2 receptor subtype. Butaprost has frequently been used to pharmacologically define the EP receptor expression profile of various human and animal tissues and cells. Serious confusion as to the structure of Butaprost was generated by Gardiner in 1986, when he reported that the epimer of butaprost showing this selective activity was the C-16 (R)-epimer (See Note). 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, FP, IP, or TP receptors.{6640} The pharmacology of (R)-butaprost has not been carefully studied, but it is generally considered to be the less active epimer.