Prostaglandin F (2-alpha) is known as a potent luteolytic agent. It is involved in modulating intraocular pressure and smooth muscle contraction in uterus. Its effects on cells are mediated through specific interaction with the Prostanoid receptor FP, which is a 359-amino acid protein. Having 7 putative transmembrane domains, FP resembles the characteristic of G protein coupled receptors. Knockout studies in mice suggest that the interaction of PGF2-alpha with this receptor may initiate parturition in ovarian luteal cells and thereupon induce luteolysis.