Effect of human placental lactogen upon the human corpus luteum of late pregnancy.

To acertain whether human placental lactogen (HPL) functions as a luteotropin during pregnancy in humans, studies were performed to determine if receptors for HPL are present in cells of the human corpus luteum of late pregnancy. Preparations of 125I-HPL which demonstrated specific binding to late pregnant rabbit mammary gland cell homogenates showed specific binding of less than 2.5% to homogenates of human corpora lutea of late pregnancy. These studies indicate that HPL is not luteotropic at this stage of pregnancy in humans. The action of HPL upon the corpus luteum appears to vary considerably according to species.