Human Placental Lactogen: Studies of Its Acute Metabolic Effects and Disposition in Normal Man*

Abstract

The acute metabolic effects and disposition of human placental lactogen (HPL) have been studied in 15 men and 8 women during continuous intravenous infusions. The mean plasma half-life, metabolic pool size, and turnover rate of HPL are comparable to the values previously reported for human growth hormone (HGH). From the data presented, we calculate that the placenta secretes approximately 290 mg HPL daily at term. After 12-hour infusions of HPL in physiologic amounts, impairment of glucose tolerance despite increased plasma insulin responses to glucose was observed in 7 of 8 subjects tested. However, HPL, unlike HGH, did not produce significant changes in blood glucose, plasma insulin, or plasma free fatty acid concentrations in fasting subjects before glucose administration or in carbohydrate tolerance or plasma insulin responses to glucose during 5-hour infusions. These findings are compatible with the thesis that HPL is a physiologic antagonist to insulin during pregnancy.