Reduced active thyroid hormone levels after delivery.

The effect of delivery on the serum concentration of thyroid hormones was studied in 25 euthyroid women. After delivery serum free and total T3 and T4 fell transiently with a simultaneous increase in reverse T3 while serum TSH and thyroxine binding globulin (TBG) concentrations showed no significant variation. These data suggest that i) similar to what happens in other stressful situations, delivery influences peripheral T4 metabolism, and ii) an elevation of TBG in serum in the early puerperium does not prevent these changes.

Conversion of thyroxine to triiodothyronine and reverse triiodothyronine in human placenta and fetal membranes.

Conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) and reverse 3,3',5'-triiodothyronine (rT3) was measured in vitro in human placenta and fetal membranes. T4 (5 micrograms/ml) was incubated in 0.15 mol/l phosphate buffer with tissue homogenates for 2 h at 37 degrees C, and the T3 and rT3 generated were determined in ethanol extract using RIA methods.

Decreased ratio of serum T3:rT3 in patients with hyperthyroidism.

In 14 hyperthyroid patient serum T4:rT3 ratio was significantly lower (399 +/- 20) than in the control subjects (572 +/- 20; p less than 0.001). A similar pattern was found for serum T3:rT3 ratio.