Summary
Plasma levels of blood coagulation zymogens are lower in the newborn than in the adult,
with the lowest levels being in preterm infants. It is not known if the lower coagulation
factor levels reflect differences in synthesis, secretion or catabolism.
Using a rabbit model we have compared prothrombin synthesis in the fetus and adult.
In previous studies we attempted to compare transcription in the adult and fetal liver
by extraction of mRNA, immobilization on a membrane and hybridization with a labeled
cDNA for rabbit prothrombin. Comparison was impaired by the markedly dissimilar composition
of fetal and adult rabbit liver; fetal liver is approximately fifty percent hematopoietic
tissue even at term (1). In the present study, to obtain a more meaningful comparison
we have employed in situ hybridization to compare directly prothrombin expression
in adult and fetal liver. We report here that fetal liver contains more prothrombin
mRNA than does adult liver. We have further compared prothrombin levels in protein
extracts of adult and fetal liver and found that per microgram of extract, fetal liver
contains as much prothrombin as does the adult. We conclude that the lower plasma
prothrombin levels in the fetus do not reflect a lower rate of synthesis.
