Figure 3
From: Pregnancy recognition signaling mechanisms in ruminants and pigs
The theory of pregnancy recognition in the pig is that secretion of prostaglandin F 2α (PGF) is endocrine, that is, toward the uterine vascular drainage to induce luteolysis in cyclic pigs. However, PGF is secreted in an exocrine direction, that is, toward the uterine lumen in pregnant pigs where it is metabolized and unavailable to exert luteolytic effects.