LH - Luteinizing Hormone

"The breeding stimulus causes the release of a hormone from the pituitary, a gland at the base of the brain. This hormone (luteinizing hormone or LH) in turn, causes the mature follicle to rupture and release the egg into the oviduct, where it is fertilized. Following this release (ovulation), the follicle fills with blood, the cells of the follicle undergo a reorganization and become a temporary hormone secreting tissue, the corpus luteum or CL. The prime hormone produced by the corpus luteum is progesterone, the most important hormone during pregnancy. If progesterone production ceases, the animal will not be able to continue the pregnancy and will abort. Blood progesterone concentrations are normally very low. As the follicle becomes a corpus luteum, its appearance and composition changes. Whereas the mature follicle was fluid-filled and fairly soft, the CL is much firmer and usually projects somewhat above the surface of the ovary. This difference in composition is an important factor in the diagnosis of pregnancy by rectal palpation. (Dr. Brad Smith)