PHARMACOKINETICS OF [I-125] RECOMBINANT HUMAN INTERLEUKIN-11 - 2 - PLACENTAL-TRANSFER AND EXCRETION INTO MILK AFTER SUBCUTANEOUS ADMINISTRATION TO RATS

Placental transfer and excretion into milk of [I-125]-rhIL-11 (recombi nant human interleukin-ll) after subcutaneous administration in female rats were investigated. After administration of [I-125]-rhIL-11 to ra ts on the 14th day of gestation, radioactivity in the kidney was the h ighest among excised tissues, being 3 times higher than that in the pl asma at 1.5 h. Radioactivity in other tissues, including the mammary g land, ovary, uterus, placenta and amniotic fluid, was lower than that in the plasma. Although radioactivity in fetuses was detected 6 h afte r administration, the level was only 2% of the plasma concentration in dams, and the radioactivity was not found in fetal-derived TCA precip itates. These results indicate that rhIL-11 does not readily pass thro ugh the placenta into the fetus. After subcutaneous administration of [I-125]-rhIL-11 to lactating rats 14 days after delivery, radioactivit y in milk was 1.1-1.6 times that in the plasma of dams. Radioactivity in clotted milk in the stomachs of suckling infants was almost equal t o that in the dam's milk; however, only a small amount of radioactivit y was detected in infant kidneys.