Development of Fibrinolytic Proteins in Health and Disease

Abstract

Beacuse of the propensity of newborn, especially low birth weight (LBW) infants, to bleeding and thrombosis, and the possibility of a fibrinolytic defect in the respiratory distress syndrome (RDS), serum proteins of the fibrinolytic system were measured in healthy term and LBW infants and compared to maternal levels and levels in sick LBW infants with and without RDS. Levels of plasminogen (PLM), two antiplasmins, alpha-2-macroglobulin (α 2-MC) and alpha-1-antitrypsin (α 1-AT) and albumin and IgG globulin were measured by radial immunodiffusion on paired maternal-cord serum of 45 term newborns, 37 LBW well newborns, 28 LBW infants with RDS, 24 sick LBW infants without RDS, and 9 immature (< 0.8 kg) infants. Term infants had PLM levels of 45 ± 14 (1 standard deviation) mg/100 ml, compared to maternal levels of 90 ± 18 mg% and adult controls of 70 ± 7 mg%. Levels of α 2-MC and α 1-AT in term infant serum were 149 ± 35% (percent of standard serum) and 132 ± 37 mg%, respectively; in maternal serum 139 ± 43% and 262 ± 48 mg%; and in adult control serum 152 ± 34% and 133 ± 22 mg%. There were significant (p < 0.01) reductions of levels of α 2-MC and PLM with decreasing birth weight; no such relationship was noted for α 1-AT. Significant correlation existed between maternal and cord levels of albumin, IgG, PLM, α 1-AT and α 2-MC, suggesting transplacental passage of these proteins. No differences were noted in levels of PLM, α 1-AT in the RDS or other ill LBW infants.

The relatively high levels of antiplasmins compared to plasminogen levels suggest impaired fibrinolysis at birth. These studies do not correlate well with prior functional studies of the fibrinolytic system, suggesting that poorly characterized activators and inhibitors play a major role in the regulaion of fibrinolysis.

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