Placental transfer of I¹³¹-insulin in the rhesus monkey

¹ Department of Physiology, Harvard Medical School, Boston, Massachusetts

Pregnant rhesus monkeys were anesthetized, their uteri were exposed, and the interplacental vessels (fetal circulation) were cannulated without incision of the amnion. This procedure permitted simultaneous sampling of maternal blood, umbilical venous blood and umbilical arterial blood. I¹³¹-labeled insulin injected into the material circulation was detected in umbilical venous plasma, within 5 minutes after the injection, by the use of a chromatographic procedure which permits the separation of I¹³¹-insulin from other iodinated compounds. The concentration of I¹³¹-insulin in fetal plasma did not exceed 20% of that found concurrently in maternal plasma. A marked umbilical arterial-venous difference in I¹³¹-insulin concentration was consistently observed. The concentration of iodinated degradation products of I¹³¹-insulin was considerably higher in umbilical arterial plasma than in umbilical venous plasma, suggesting rapid degradation of the labeled hormone by the fetus. Conversely, the injection of I¹³¹-insulin into the fetal circulation was followed by the appearance of significant quantities of the labeled hormone in the maternal circulation. These experiments lead to the conclusion that insulin can cross the primate placenta.