The metabolism and kinetics of 125I-labeled intravenous human IgG preparation (C-425) in rats and rabbits. II. Excretion into bile, tissue distribution and placental permeability.

The metabolism and kinetics of unmodified human IgG (125I-C-425) was studied in rats and rabbits after intravenous injection with regard to changes as a function of time of radioactivity in the blood and other tissues, excretion into the bile and placental permeability. A microautoradiographic study on the cellular interaction between 125I-C-425 and rat tissues was also performed using 125I-Polyglobin as the control drug. Results showed plasma radioactivity to be the highest followed by blood, lung, heart, kidney, bone marrow etc. in decreasing order. Tissues considered to contain larger amounts of blood, gave higher radioactivity values with some exceptions, such as the thyroid and skin. Biliary excretion within 72 hours was 7.57% for 125I-C-425 and 10.74% for 125I-Polyglobin. In pregnant rats, relatively high radioactivity was counted in the ovarium, uterus and placenta, and radioactivity in the fetus and amniotic fluid approached that of uterus and placenta up to 72 hours, indicating that placental permeability was gradual. Microautoradiographic findings revealed no cellular interaction such as aggregate formation, between human IgG and rat tissues. Further study is needed to elucidate immunological interaction under pathological conditions.