Transplacental permeability of 125I-sfericase in mice

125I-sfericase was administered intravenously into the tail vein of mice on day 20 of gestation at a dose of 1 mg/kg as sfericase. The penetrability of sfericase into the placenta, radioactivity levels, and precipitable high molecular 125I treated with TCA were measured in maternal blood and plasma and fetal homogenates collected at 20 and 90 min after i.v. injection. The radioactivity level in fetuses was considerably lower than that in dams at 20 min but almost comparable to that of dams at 90 min, indicating considerably good penetrability of the radioactivity into the placenta. However, after treatment with TCA, the content of high molecular 125I in fetuses was considerably lower than that in maternal blood. These results suggested that high molecular 125I degraded into a low molecular fraction while passing the placenta to reach the fetus.