Plasma immunoreactive beta-endorphin and cortisol in the newborn infant after elective caesarean section and after spontaneous labour.

The effect of the mode of delivery on the plasma concentration of immunoreactive beta-endorphin (irbeta-E) and cortisol was studied in 27 newborn infants, 10 delivered by caesarean section and 17 by spontaneous vaginal labour. After elective caesarean section, the mean plasma concentration of cortisol rose from 227 +/- 27 nmol/l (S.E.) at birth to 705 +/- 90 nmol/l at the age of 2 h, indicating a significant increase in cortisol secretion, and the mean irbeta-E remained high, being 111 +/- 24 ng/l at birth and 117 +/- 21 ng/l at the age of 2 h. After spontaneous labour, the plasma cortisol level was already high at birth, 735 +/- 78 nmol/l, and remained so to the age of 2 h, 659 +/- 43 nmol/l, whereas the plasma irbeta-E decreased from 181 +/- 29 at birth to 64 +/- 7 ng/l at the age of 2 h. All newborns were in a good condition except one in whom transitory tachypnea developed during the follow-up. In this newborn the plasma level of irbeta-E increased greatly: from 210 ng/l to 705 ng/l. These results show that, irrespective of the route, the delivery is stressfull to the newborn infant. In newborns delivered by caesarean section the stress response comes after birth. Additional stress such as respiratory difficulties seems to increase the secretion of beta-endorphin.