THYROXINE AND FETAL BLOOD-COAGULATION - A FETAL LAMB STUDY

Glucocorticoids have been shown to accelerate the development of blood coagulation in the fetal lamb (Kisker, Robillard & Bohlken, 1983). Th e current studies examine the influence of high levels of triiodothyro nine (T3) on the development of blood coagulation in the fetal lamb. E ight twin fetal lambs were studied during the last trimester of pregna ncy (109-138 days gestation) using chronically placed arterial and ven ous catheters for infusion of T3 and withdrawal of blood samples. One fetus of each twin was infused intravenously with T3 at a constant rat e of 0.6 mug T3/0.4 ml/h for 48 h. The other twin was infused with 5% dextrose at 0.4 ml/h for 48 h. Blood samples for measuring PT, PTT, TT , fibrinogen, factors II, V, VII, VIII, IX, X, XI and XII were obtaine d prior to and at the completion of the infusions. The results were an alyzed for differences between the samples from paired control and T3 treated animals. Factor V significantly decreased in the T3 infused an imals from 51.2% +/- 12.5% to 44.8% +/- 13.8% (P=0.038). Factor VII al so decreased in the treated animals 57.8% +/- 20% to 43.6% +/- 10.8%, but the changes were not statistically significant (P=0.06). Factor XI I significantly increased in the treated animals from 37% +/- 10.5% to 45% +/- 13.7% (P=0.004). High levels of T3 in third trimester fetal l ambs are accompanied by a moderate decrease in factor V and an increas e in factor XII activity.