Catabolism of fibrinogen in pregnant rabbits before and after delivery.

16 non-pregnant female and 19 pregnant rabbits were injected with purified rabbit 125I-fibrinogen in order to study the catabolism of fibrinogen before and after delivery. The half-life time (T 1/2) of the clottable 125I-radioactivity in pregnant rabbits during the last third of gestation was 27.3 +/- 5.3 hr in comparison to 54.4 +/- 3.7 hr in non-pregnant rabbits. After delivery, T 1/2 returned to normal values of 47.9 +/- 10.9 hr. The fractional catabolic rate (FCR) of the clotabble 125I-radioactivity was 67.1% X d-1 +/- 8.6 before and 41.6% X d-1 after delivery whereas FCR in non-pregnant rabbits amounted to 44.7% X d-1 +/- 4.8. These figures demonstrate a pronounced increase in fibrinogen catabolism during the last third of gestation in pregnant rabbits and a normalization immediately after delivery. Although in pregnant rabbits the elimination of fibrinogen from the circulating blood was pronouncedly increased, the plasma fibrinogen concentration did not change. Only after delivery did the fibrinogen concentration increase when the fibrinogen catabolism had already normalized.