Release of a substance from the human placenta having digoxin-like immunoreactivity.

1. The human placental lobule, perfused with a constant flow (5 mL/min) of Krebs' solution after delivery at term, released into the fetal perfusate a digoxin-like substance, as measured by a fluorescence polarization immunoassay. 2. Initially the venous concentration was 360 +/- 66.7 pmol/L digoxin equivalents. This level did not change significantly during fetal vasoconstriction induced by prostaglandin F2 alpha infusion and persisted for the duration of the experiment (1.5-2 h). 3. Infusion into the fetal circulation of Fab fragments of sheep antibodies to digoxin caused vasodilatation, indicated by a fall in perfusion pressure. 4. Thus a digoxin-like immunoreactive substance, previously reported to be present in the placenta, is released into the fetal circulation and may play a role in placental control of fetal vascular tone.