Control of luteal function during early pregnancy in sheep.

: Prolactin and LH are required for the maintenance of normal luteal structures during early pregnancy in the ewe, whilst luteolysis, induced by prostaglandin F-2 alpha is inhibited by the presence of the conceptus. The trophoblast also secretes a local anti-luteolytic factor, trophoblastin, which is most probably a protein because it is thermolabile and inactivated by pronase. It is soluble at pH 9.6 and can be separated on Ultrogel. Trophoblastin is present for a short time (12th-22nd day of pregnancy) but its effect may last several months.