Fibrinogen turnover in pregnant rabbits during the first and last thirds of gestation.

Although thrombin-mediated fibrinogen derivatives have been observed in normal pregnancy, an increased turnover of fibrinogen has been suspected but has not yet been demonstrated. Fibrinogen turnover was studied in 14 pregnant and 10 nonpregnant female rabbits by use of purified rabbit 125I-labeled fibrinogen. In the last third of gestation the half life of fibrinogen was shortened by 45% and the fractional catabolic rate increased by 44% in comparison to the values for the first third of gestation obtained in the same rabbits. The distribution volume of the injected fibrinogen representing the plasma volume increased by a mean of 18% during gestation. Fibrinogen concentration did not change during gestation. From a comparison of the measured data from the first and last thirds of gestation, it can be calculated that the synthesis rate of fibrinogen increased by about 80%. Furthermore, a positive correlation was found between the number of young per litter and the acceleration of fibrinogen elimination, indicating that a local process of intravascular coagulation in the placenta is responsible for the accelerated turnover of fibrinogen during gestation.