The placental binding and transfer of radiopharmaceuticals II: Tc-99m Sestamibi, Tc-99m Tetrofosmin and Tl-201 Thallous Chloride

It has been shown that some radiopharmaceuticals can cross the placental barrier and enter into fetal circulation. The objective of this study was to investigate placental transfer of car diac perfusion imaging radiopharmaceuticals (Tc-99m sestamibi, Tc-99m + tetrofosmin and TI-201 thallous chloride (Tl -201)) in pregnant guinea pigs and in-vitro mechanism of the transfer using human placental lobule. Pregnant guinea pigs in the first, second and third trimesters were used. Following intravenous injection of Tc-99m sestamibi, Tc- + 99m tetrofosmin or Tl -201 the guinea pig was imaged using a gamma camera; killed and the fetuses removed. Each fetus was then imaged separately using a low energy general-purpose collimator. The placentas, ovary, and fetal hearts, lungs, liver, kidneys and blood were then removed and the radio-activity in each organ along with a 1.0 ml standard solution was counted separately in a dose calibrator. For the in-vitro experiment, the effect of ouabain + 50 parameters were also measured: the area under the curve, clearance and absorption rate indices. Neither Tc-99m sestamibi nor Tc-99m tetrofosmin was transferred across the placental barrier while 1.7 + 0.5% of the injected + activity (0.027 + 0.005 % per gram) of Tl -201 radioactivity during the third trimester was transferred across the placenta into fetal circulation. Most of the + radioactivity from Tl -201 in the fetus was in the liver, followed by the heart. For the in-vitro experiment, TR 50 + index of Tl -201 averaged 0.98 + 0.05 for normal perfusion and corresponding index for ouabain-treated was 1.17 + 0.03; the difference was statistically significant (p<0.05) + thereby implying a significantly reduced rate of Tl -201 transport in the ouabain-treated lobules. The area under the curve (AUC), clearance and absorption rate indices of control perfusion were 4.12 + 0.52, 0.62 + 0.06 and 2.75 + 0.12, respectively and the corresponding indices for ouabain-treated perfusion were 1.89 + 0.28, 1.65 + 0.12 and 1.64 + 0.18, respectively and the differences were statistically significant (p< 0.05) also implying that + ouabain treatment reduced transport of Tl -201 in the human placental tissue in the maternal-fetal direction The +