Change in circulating β-endorphin and cortisol in preterm infants: Lack of association with intrauterine-like sound stimulation

Abstract

Exposure to intrauterine-like sound has been reported to be beneficial to newborn babies. As part of a larger study to develop methods to reduce arousal and stress experienced by sick, newborn babies, we evaluated the hormonal responses to intrauterine-like sound in a group of babies receiving intensive care. Plasma β-endorphin and cortisol concentrations were measured in nine preterm babies (median gestational age 27 weeks) (i) before, (ii) at the end of, and (iii) 1 hour after the end of a 30-minute period of intrauterine-like sound stimulation. There was a very wide range of basal plasma cortisol concentrations (15-1270 nmol l-1) and β-endorphin concentrations (80-550 pg ml-1). The highest concentrations were seen in the most severely ill baby. There was no significant change in either cortisol or β-endorphin in response to sound stimulation. A highly significant correlation existed between cortisol and β-endorphin concentrations at both the basal and after-stimulation states (r= 0.92 and 0.87 respectively, p < 0.005). As there is increasing evidence that prolonged exposure to elevated glucocorticoid concentrations may be harmful, and that permanent alterations in hypothalamic-pituitary-adrenal axis function may occur as a result of early neonatal experiences, more work is necessary to define the metabolic responses of infants in intensive care and to examine techniques which may be of positive benefit.