Distribution of Radioactivity in Human Maternal and Fetal Tissues Following Administration of C14-4-Progesterone.

Summary C14-4-progesterone was administered intramuscularly to pregnant women who were scheduled for therapeutic abortion. Distribution of radioactivity in maternal and fetal tissue removed at various time intervals following injections was determined. The highest concentration of radioactivity was found in the maternal fat. A rough calculation revealed that it contained about 17.7% of the administered radioactivity 12 hours. 33.7% 24 hours, and 19.6% 48 hours after administration of the labelled hormone. These findings indicate that progesterone and or its metabolites diffuse promptly from the blood circulation into the fat compartment of the body. Only moderate amounts of radioactivity were found in the myometrium and the decidua. the 2 principal target organs of progesterone. Low to moderate concentrations of radioactivity were detected in the organs which serve as principal sources of the hormone, the corpus luteum and the placenta. Radioactivity was present in all fetal tissues in relatively small amounts with the exception of the fetal brain, and the testes.