Function and Ultrastructure of Platelets of Neonates: Enhanced Ristocetin Aggregation of Neonatal Platelets

Abstract

We have investigated platelet morphology and function in human maternal-newborn pairs. Fibrinogen concentration and factor-VIII activity in plasma were also determined. Our results showed that, compared to maternal platelets, neonatal platelets were poorly responsive to adenosine diphosphate, adrenaline and collagen. Uptake of labelled serotonin by neonatal and maternal platelets was the same, but release of the radioactivity was reduced in the former. Phagocytic activity of neonatal platelets, demonstrated with latex particles, was similar to that of maternal platelets. Although the ultrastructure of neonatal platelets approximated that of maternal platelets, immature appearing platelets were occasionally found in the neonatal samples. An unanticipated finding was that platelet aggregation induced by ristocetin was more vigorous in neonatal than in maternal platelet-rich plasma samples. Furthermore, neonal -lasma, which had lower fibrinogen and factor-VIII content than maternal plasma, facilitated maternal platelet aggregation by ristocetin and showed a greater ability than maternal plasma to promote ristocetin-induced aggregation of platelets of a patient with von Willebrand's disease. These results indicate that the plasma of neonates contains large quantities of the ristocetin-dependent platelet aggregation factor (RAF), probably more than is in maternal plasma, despite the higher levels of factor-VIII procoagulant activity in the latter. Thus, in the newborn, there is a clear dissociation between factor-VIII clotting activity and the RAF activity.

Platelet Serotonin in Newborns and Infants: Ontogeny, Heritability, and Effect of In Utero Exposure to Selective Serotonin Reuptake Inhibitors

“…It is not clear whether the early increase in 5-HT is due to a change in the platelet's handling of 5-HT or to an increased exposure to 5-HT. There are some very limited data that suggest 5-HT platelet uptake is fully functional in newborns (27) and that the gut's production of 5-HT (as indexed by urinary 5-hydroxyindoleacetic acid) is lower in the first week of life (28). These reports suggest that the early rise may be due to increased exposure, and this would be consistent with the expected increase in gut 5-HT release as feeding begins (29 -31).…”

Contractile Activity of Neonatal Platelets

“…These results suggest that the components of platelet function necessary for contractile activity are present in term infants (237 wk gestation). Although platelet aggregation studies were not performed on these cord blood samples, due to constraints of sample volume, multiple reports have confirmed abnormalities in neonatal platelet aggregation responses by well-established methodology (3)(4)(5)(6). Therefore, this present study suggests that the previously described abnormalities of neonatal platelet aggregation are unlikely to be the result of defects in mechanisms shared by the aggregation and contraction processes, i.e.…”

“…The differences in clotting factor activity and fibrinolytic enzymes between cord blood and that of adult controls are well established (1,2). Abnormalities in neonatal platelet function have been demonstrated using both cord blood and venous samples from newborn infants (3)(4)(5)(6). These abnormalities include impaired aggregation responses to stimuli such as collagen, epinephrine, and ADP.…”

Antithrombotic Therapy in Neonates and Children

“…182,183 Paradoxically, the bleeding time is short in newborns because of increased RBC size, high hematocrit levels, and increased levels of multimeric forms of von Willebrand factor. [184][185][186] The bleeding time was prolonged, relative to adults, throughout childhood in two of three studies. 34,187,188 Using the platelet function analyzer (PFA)-100 (Dade International, Inc), cord blood samples from term neonates were found to have shorter closure times than samples from older children or adults.…”