The reaction of platelets to bilirubin and its photodegradation products was investigated. Based on the results showing in Figure 1, various concentrations of bilirubin were added to gel filtration platelets solution (GFP). The most intence aggregation was induced by 5-10mg/dl of bilirubin at final concentrations (f. c.) in GFP from adult blood, whereas it was induced by 0.5-1.0mg/dl of bilirubin (f. c.) in GFP from umbilical blood. The less intence aggregation was induced by photodegradation products of bilirubin, and no aggregation wasobserved after exposure to light for 80 minutes or longer.
Bilirubin induced GFP aggregation was inhibited perfectly or partially by addition of albumin, ethanol, prostaglandin E₁, prostaglandin I₂, aspirin and flurbiprofen. Heparin enhanced the aggregation at low concentration (≤20units/ml), but inhibited it at high concentration (≥40units/ml). However, dl-α-tocopherol (≤300mg/dl) had no inhibitory effect on the aggregation.
¹⁴C-labelled serotonin was released after exposure to light in platelet rich plasma from umbilical blood, but not in platelet rich plasma from adult blood.
Those results indicate that phototherapy may induce DIC by activation of platelets, especially in neonates.