Prostaglandin F2α (PGF2α), acting through the FP receptor, causes smooth muscle contraction and exhibits potent luteolytic activity. Both 17-phenyl trinor PGF2α and 16-phenoxy tetranor PGF2α are metabolically stable analogs of PGF2α and potent agonists for the FP receptor. 17-phenoxy trinor PGF2α ethyl amide is a lipophilic analog of 17-phenoxy trinor PGF2α . Ethyl amides of PGs serve as prodrugs, as they are hydrolyzed in certain tissues to generate the bioactive free acid.