Development of Coagulation Regulatory Proteins in the Fetal and Neonatal Lamb

Abstract

To investigate the development of coagulation regulatory proteins-protein C (PC), protein S (PS), and antithrombin (AT)-in relationship to the procoagulant protein factor X (FX), a chronically catheterized fetal ovine model was used. Infusion and sampling catheters were placed into pregnant ewes and their fetuses and maintained from mid-gestation. From a total of 110 fetuses, 17 lambs, and 63 ewes that were studied on one to 15 occasions, 212 fetal, 88 neonatal, and 157 maternal samples were obtained. Liver tissue was obtained from 31 fetuses and 15 ewes. Plasma levels of all proteins studied were higher in the ewe than in the fetus (p Ͻ 0.0001). Plasma levels of FX, PC, and PS achieved neonatal levels by mid-gestation with mild but significant decreases during mid-and late gestation. Fetal and early neonatal plasma concentrations of these vitamin K-dependent proteins fit a model with both quadratic (p Ͻ 0.01) and linear (p Ͻ 0.01) components. The discrepant levels in mRNA relative to plasma concentration were consistent with regulatory control beyond the level of transcription. In contrast, a simple linear increase in plasma protein levels was determined for the vitamin K-independent coagulation regulatory protein, AT (p for quadratic component Ͼ 0.05). This study suggests that fetal regulation of coagulation proteins follows characteristic patterns relative to the vitamin K dependence of the protein rather than its role as a procoagulant versus regulatory protein. The hemostatic systems of the fetus and neonate differ from that of the adult. Plasma concentrations of coagulation proteins mature at different rates during in utero and postnatal development (1-3). In particular, vitamin K-dependent factors, prothrombin, PC, PS, and factors VII, IX, and X, as well as contact factors XI, XII, prekallikrein, and high-molecular-weight kininogen, are present in very low concentrations in the fetus and do not achieve normal adult levels until later infancy to adolescence (2-7). Clinically, the well neonate has a functionally intact hemostatic system. However, the stressed infant demonstrates an increased predisposition to thrombosis, both induced and spontaneous (8). The increased rate of thrombosis in neonates is generally attributed to physiologically low levels of coagulation regulatory proteins, particularly PC, PS, and AT.PC is a vitamin K-dependent serine protease that serves a critical role in the regulation of coagulation. Activated PC, with its cofactor PS, inactivates activated procoagulant factors V and VIII (9). Infants with severe genetic deficiencies of either PC or PS manifest spontaneous thrombosis in utero or within hours of birth (10, 11). Our previous work showed that the mean concentration of PC in the extremely preterm infant is 0.20 U/mL, as compared with 1.00 U/mL in healthy adults (6, 7). An increased risk of catheter-related and spontaneous thrombosis was demonstrated in preterm infants with plasma concentrations of PC Ͻ0.10 U/mL (7).AT is an essential regulatory protein that functions through i...

Pharmacokinetics of Protein C and Antithrombin in the Fetal Lamb: A Model to Predict Human Neonatal Replacement Dosing

“…We chose a fetal ovine (lamb) model to compare plasma recovery and elimination following infusion of replacement concentrates of these proteins in comparison to ewes. Previous studies of coagulation proteins in fetal and adult sheep (ewes) in our lab have shown good comparability with human (preterm and term neonate, child, adult) data [31][32][33] .…”

“…We previously reported that ovine PC and AT can be detected in plasma of fetal lambs at 70 days of gestation (term gestation is 147 days) [33] . In that study, AT plasma concentrations increased linearly with gestational age.…”

“…A standard ovine plasma pool was prepared from 26 healthy nonpregnant adult sheep. Normal adult values for ovine PC and AT were derived from these individual plasma samples, with the pool mean expressed as 1 U/ml as previously described [33] . Study samples were read against curves constructed using dilutions of the normal ovine pool.…”

Topical Review: Animal Models of Germinal Matrix Hemorrhage

“…Hemostasis and hemostatic proteins differ between the fetus (and premature infant) and the term infant. [92][93][94] To date, there has been little consideration of how these differences might impact on the ultimate brain damage after hemorrhage. 5.…”