Presented at the Neonatal Society 2005 Spring Meeting.
Armstrong L1, Smith J2, Midgley P2, Hoftijzer D2, Wilson C2 (introduced by A Lyon)
1 Simpson Centre Reproductive Health, New Royal Infirmary, Edinburgh EH16 4SA, UK
2 University of Edinburgh, New Royal Infirmary, Edinburgh EH16 4SA, UK
Background: Measurement of total cortisol concentration is traditionally used as an index of infant stress response (1). However the majority of cortisol measured is protein bound and unable to bind receptors. Adult data demonstrate that protein binding of cortisol can decrease rapidly during physiological stress2. The acute phase proteolysis of these carrying proteins can potentially liberate large quantities of hormone to bind receptors. We hypothesise that total cortisol concentration alone is insufficient as an index of ‘stress response’, and must be taken in the context of its protein binding.
Aim: We have developed a radioimmunoassay to measure the capacity of specific and non specific proteins to bind cortisol, or CBC in plasma. CBC directly influences the relative quantities of bound and unbound cortisol in plasma. In this study we examine infants response to perinatal stressors by looking at the protein binding as well as total concentration of cortisol.
Methods: Prospective study with written parental consent. CBC and total cortisol were measured using in-house RIA based on principles of saturation analysis.
Subjects:96 healthy singleton infants. Modes of delivery: SVD 48, instrumental delivery (INST) 15, emergency caesarean section (EMCS) 20, elective caesarean section (ELCS) 13. Mean gestation 40.1 weeks, mean weight 3501 grams.
Results: Protein binding of cortisol (CBC) was not influenced by mode of delivery, or other factors (see fig.1). Mean (SEM) CBC was 42.8 (2.1) nmol/l. A stepwise regression analysis model showed that duration of second stage of labour (p<0.01), need for spinal anaesthesia (p<0.01) and meconium staining (p=0.05), independently predicted total cortisol concentration. Total cortisol concentrations were significantly higher for SVD when compared with emergency caesarean section (p<0.01 ANOVA).
Conclusion: Total cortisol concentration is highest in the cord blood of infants born by SVD and lowest in those born by caesarean section without labour. Protein binding of cortisol, however, is unaffected by these factors and does not further influence the free fraction during the birth process. Despite manifest H-P-A activation at delivery, there is no evidence of dynamic changes in the respective protein binding.
References
1. Mears K et al. J Obs Gyn vol. 24, No. 2, 129-132 2004
2. Hamrahian AH et al. N Engl. J. Med. 350(16):1629-38, 2004 Apr 15