Salivary and serum cortisol and relation to blood pressure in infancy and early childhood in very-low-birth-weight infants

BACKGROUND: Programming of the hypothalamic-pituitary-adrenal (HPA) axis possibly explains the relation between intrauterine growth restriction (IUGR) and/or preterm birth and elevated blood pressure in later life. Very-low-birth-weight infants (birth weight <1,500g) have high prevalence of raised blood pressure, already in early childhood. We investigated cortisol levels, relation to blood pressure and reliability of salivary cortisol in infancy and early childhood in very-low-birth-weight infants. METHODS: We included 41 children, participating in the randomized controlled Neonatal Insulin Replacement Therapy in Europe (NIRTURE) trial. Serum and salivary samples for cortisol measurement (immunoassay) were taken simultaneously at 6 mo and separately at 2 y corrected age. Blood pressure was measured at 2 y corrected age. RESULTS: Serum cortisol was significantly correlated to systolic and diastolic blood pressure in boys and in the early-insulin treated group. At 2 y corrected age serum cortisol was significantly higher in the early-insulin group compared to the standard care group. At 6 mo corrected age salivary cortisol was significantly correlated to serum cortisol. CONCLUSION: In very-low-birth-weight boys, the positive correlation between cortisol and blood pressure is present at 2 y corrected age. Early insulin therapy could affect programming of the HPA axis. Salivary cortisol mirrors serum levels at 6 mo corrected age.