Cumulated activities determined from biodistribution data in pregnant rats ranging from 13 to 21 days gestation. I. Tc-99m pertechnetate.

Cumulated activity estimates for Tc-99m pertechnetate were determined using biodistribution data from pregnant and nonpregnant rats. The pregnant rats were studied at 13, 15, 17, 19, and 21 days gestation. The results indicate that maternal organ cumulated activities are not a simple function of gestational age. The organs into which Tc-99m pertechnetate enters through passive diffusion follow the pattern established by the blood, generally resulting in an increase from the 13th through the 17th day with a decrease on the 19th and 21st day. The organs dominated by active transport follow unique and different patterns. The fetal cumulated activity estimates increased exponentially with gestational age and the placental estimates increased linearly.