Immunoreactive thromboxane B2 and 6-keto-prostaglandin F1 alpha in neonatal hyperbilirubinemia.

To study the effects of hyperbilirubinemia on platelet thromboxane A2 (TxA2) and vascular prostacyclin (PGI2) production in newborn infants, the stable metabolites of these prostanoids, thromboxane B2 (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), respectively, were studied in 48 hyperbilirubinemic (serum total bilirubin concentrations between 100 and 320 mumol/1) term infants before and after phototherapy at the age of 2-10 days. The effect of bilirubin on platelet TxA2 production was also determined in vitro. The production of TxB2 during spontaneous clotting in infants with moderate hyperbilirubinemia (serum total bilirubin 171-250 mumol/1) was higher than that in infants with mild (serum bilirubin 100-170 mumol/1) or marked (serum bilirubin greater than 250 mumol/1) jaundice. There was, in addition, an inverse correlation (r = -0.625, p less than 0.01, n = 20) between TxB2 formation and serum total bilirubin concentrations in infants with total bilirubin concentrations over 170 mumol/1. Platelet TxB2 production was enhanced at low (200 mumol/1), but decreased at high (400-1600 mumol/1) concentrations of bilirubin in vitro. Although phototherapy reduced the serum bilirubin levels, it did not change the TxB2 generation. Neither hyperbilirubinemia nor phototherapy had any effect on the plasma 6-keto-PGF1 alpha levels. The results indicate a dual effect of bilirubin on the TxA2 production in neonatal platelets. This may contribute to the hemostatic disturbances in neonatal hyperbilirubinemia.