Plasma β-Endorphin in Perinatal Asphyxia and Respiratory Difficulties in Newborn Infants

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Abstract
The effects of intrauterine stress and birth asphyxia on the plasma concentration of β-endorphin (β- 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 β-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 β-E level varied widely at birth, from 9.7 to 108 pmol/liter. At the age of 2 h, the β-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 β-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 β-E level was found, the β-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 β-E secretion is associated with respiratory difficulties in the newborn infant.