ABSTRACT. The effects of intrauterine stress and birth asphyxia on the plasma concentration of P-endorphin (P-E) in cord blood and in venous blood at the age of 2 h was investigated in newborn infants. Term infants with acute birth asphyxia (n = 11), infants born to mothers with preeclampsia (n = 15), and prematures with respiratory difficulties (n = 4) were entered into the study. Twenty control infants were studied; 12 were born after spontaneous delivery and eight after elective cesarean section. After normal spontaneous delivery, the plasma 8-E level decreased significantly, the median values being 17 pmol/ liter at birth and 9.3 pmol/liter at the age of 2 h, whereas after elective cesarean section it remained unchanged (13 and 13 pmol/liter, respectively). In acute asphyxia the plasma P-E level varied widely at birth, from 9.7 to 108 pmol/liter. At the age of 2 h, the P-E level was high (26 to 83 pmol/liter) in those asphyctic infants who required prolonged mechanical ventilation, but it fell to the range of 1.6-13 pmol/liter when the infant recovered rapidly. The P-E level was not increased in the preeclampsia group, not even in small for gestational age infants. In preterm newborn infants with respiratory difficulties, a significant postnatal rise of plasma P-E level was found, the P-E value varying from 7.3 to 16 pmol/liter at birth and from 61 to 168 pmol/liter at the age of 2 h. These results indicate that increased P-E secretion is associated with respiratory difficulties in the newborn infant. (Pediatr Res 20: 577-580, 1986)
AbbreviationThe pituitary gland secretes /3-E concomitantly with /3-lipotropin and corticotropin (I), and the secretion increases, e.g. in physical exercise (2) and during labor (3,4). Acute birth asphyxia has been found to increase plasma 0-E concentration in umbilical cord blood (5, 6). After birth, plasma level of 0-E is higher in newborn infants than in adults (7,8) but the role of this increased (3-E secretion in the early neonatal period is unclear. The effects of (3-E in newborn infants has been studied by administration of naloxone, a potent opioid receptor blocking agent. In rabbits naloxone has been found to reverse postnatal depression caused