Permeability of the sheep placenta to 125I-arginine vasopressin

We studied the permeability of the ovine placenta to AVP. 125I-AVP (9.3 +/- 1.9 mU) with approximately 82 (+/- 17.3) X 10(6) counts per 5 min were infused intravenously in 6 pregnant ewes. Six blood samples were collected at 10-min intervals over a 1-hour period from chronically catheterized maternal and fetal sheep. 125I-AVP in maternal and fetal plasma samples (1 ml each) were counted in a gammacounter for 5 min. Maternal counts decreased from 9,300 to 2,500 counts per 5 min over the hour following infusion but no increase in radioactivity could be measured in fetal blood, indicating that the sheep placenta is impermeable to 125I-AVP.