Human placental thyroxine inner ring monodeiodinase in complicated pregnancy

Production of rT3 from T4 in the placenta were measured in four patients with induced abortion, in three patients with spontaneous abortion, in 19 patients with various complications of pregnancy including Graves' disease, and in 18 normal pregnancies. The placentas, obtained at delivery, were homogenized and centrifuged at 800 X g. Supernatants (1 mg protein) were incubated with 1 microgram of stable T4 and 50 mmol/L dithiothreitol at 37 degrees C for 60 minutes. The generated rT3 was measured by radioimmunoassay (RIA). In patients who delivered at 38 to 41 weeks with complicated pregnancy, the net placental rT3 production from T4 was 7.3 +/- 2.5 ng/tube, which was not significantly different from that obtained in normal pregnancy (8.5 +/- 2.4) at an equivalent gestational age. In patients with abortions, the net placental rT3 generation from T4 was very high, and there was a significant negative correlation between the net placental rT3 production from T4 and gestational age. These results indicate that the net placental rT3 production from T4 is not affected by complications of pregnancy, but shows a significant change with the progress of gestation.