Presence in the Human Placenta and Term Serum of a Highly Lactogenic Substance Immunologically Related to Pituitary Growth Hormone

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Abstract
A previously undescribed substance has been discovered in the peripheral and retroplacental sera of human pregnancy at term. This substance is immunochemically closely related to human pituitary growth hormone (HGH) and has been isolated in relatively large amounts and purified form from term human placentas. It is highly lactogenic both in pigeon crop sac assays (local intradermal injections) and in milk-promoting activity in the pseudopregnant rabbit, but is devoid of growth-promoting activity in the hypophysectomized rat tibial plate growth assay at the dose levels tested. The possible biologic role of this lactogenic material in pregnant primates is discussed. The findings encountered give further support to the theory that a small portion of a protein hormone molecule may determine major differences in its physiologic function.