Adrenocorticotropic activity of an extract from sheep placental tissue at term

We have performed experiments to determine possible adrenocorticotropic activity in placental tissue of a sheep at term. The placental tissue was homogenized and extracted with 0.1 mmol/L of ammonium bicarbonate. The adrenocorticotropic activity of the term placental extract was compared to that of the vehicle (saline solution) and synthetic adrenocorticotropic hormone (ACTH). A single bolus injection of term placental extract had no significant effect on the plasma concentration of cortisol or progesterone. In a separate protocol, a bolus injection of ACTH was administered before and after a 48-hour continuous infusion of term placental extract, ACTH, or saline solution. The infusion of term placental extract or ACTH caused a significant increase in the basal cortisol and progesterone concentrations and a greater progesterone response following the second ACTH bolus. In vitro, the isolated adrenal cells from the term placental extract- and ACTH-infused animals showed a significantly greater ability to produce cortisol in the presence of exogenous substrate and ACTH. We concluded that placental tissue from sheep at term contains a substance which, when infused in vivo, has a corticotropic effect on the adrenal glands.