Receptor for prostaglandin F2-alpha (PGF2-alpha). The activity of this receptor is mediated by G proteins which activate a phosphatidylinositol-calcium second messenger system. Initiates luteolysis in the corpus luteum. Isoform FP-A and isoform FP-B have identical ligand binding properties but different G protein coupling properties. Expression is high in the midluteal phase corpus luteum and decreases during luteolysis. Shows agonist-independent constitutive activity, but is still responsive to agonist. Belongs to the G-protein coupled receptor 1 family.