THE ROLE OF THE HUMAN PLACENTA IN THE TRANSFER AND METABOLISM OF INSULIN*

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Abstract
The transfer of insulin-I131, iodide131 and radioiodinated serum albumin across the placentral barrier wasstudied in 28 patients. Tracer amounts of labeled material were injected or infused to the mother 7 minutes to 4 hours prior to delivery. The trichloracetic soluble breakdown products of insulin-I131 as well as iodide131 equilibrated rapidly between mother and fetus while only minute amounts of labeled trichloracetic precipitable material were found in fetal plasma after the administration of insulin-I131. Significant amounts of labeled material were trapped by the placenta after the injection of insulin-I131, but not after the injection of iodide131 or radioiodinated serum albumin. The bound labeled material present in the placenta after the injection of Insulin-I131 was rapidly degraded when placental slices or homogenates were incubated at 37.5[degree]C. The addition of reduced glutathione to the system increased the rate of degradation. The placental barrier at term is relatively impermeable to insulin. The human placenta traps and degrades significant amounts of insulin in vivo.