The Platelet of the Newborn Infant 5-hydroxytryptamine Uptake and Release

Summary

It is well recognized that some newborn infants experience unexplainable bruising, petechiae, and occasionally, intraventricular hemorrhage.

Total endogenous 5-hydroxytryptamine (5-HT) and ¹⁴C-5-HT uptake and release Aver e studied as part of a comprehensive survey.

Total endogenous 5-HT levels were assayed in platelets of normal adult subjects, parturient mothers, and full-term normal newborn infants. Mean values expressed as micromoles per 10¹¹ platelets were 0.186 ±0.018 (S.E.), 0.138 ±0.02, and 0.069 ± 0.008 respectively. Mean values expressed as nanomoles per milligram platelet protein were 0.417±0.03 (S.E.), 0.371 ±0.04, 0.161 ±0.02, respectively. No significant difference was noted between samples from adult controls and those from mothers. Newborn platelets were significantly different from either adult control platelets or maternal platelets.

¹⁴C-5-HT binding was measured in platelet-rich plasma (PRP) in the three groups. No significant difference between the three groups was noted. ¹⁴C-5-HT release following addition of solubilized collagen to PRP was measured in each of the three groups. No significant difference was noted in samples from adult normal controls (mean value 53.2 ±2.5%) and samples from mothers who had not ingested aspirin or other drugs (mean value 53.7 ±3.4%). Newborn platelet samples in contrast did not release as completely as platelet samples of the other two groups (mean value 37.2±2.4%).

Newborn platelets have both low serotonin stores, which may reflect immaturity of intestinal secretory function or block in amine synthesis, and an intrinsically defective reíase reaction which may reflect immaturity of membrane structure. Both these findings may provide further insight into altered hemostasis in the newborn.

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