19(R)-hydroxy PGF2α, an ω-1 hydroxylase metabolite of PGF2α present in human semen, exhibits a concentration of approximately 20 µg/ml for both 19(R)-hydroxy PG compounds (F2α and F1α) in fresh samples. This compound demonstrates no activity at the FP receptor of the cat iris sphincter muscle at concentrations up to 1 µM.