Relation of Respiratory Distress Syndrome to Cord Blood Levels of Adrenocorticotropic hormone and Cortisol in Preterm Neonates

Abstract

Summary C ortisol is a steroid hormone, known as a glucocorticoid, made in the cortex of the adrenal glands and then released into the blood which transports it all round the body. It regulates a wide range of processes throughout the body including metabolism and the immune response (Scott, 2011). Adrenal cortisol production is regulated by adreno-corticotropic hormone (ACTH) which is synthesized by the pituitary gland in response to hypothalamic corticotropin-releasing hormone (CRH). Serum cortisol in turn inhibits the production of both CRH and ACTH (negative feed-back loop) and this system self-regulates to control the proper level of cortisol production. The coordinated stimulatory and inhibitory connections between CRH, ACTH and cortisol are referred to as the hypothalamic-pituitary-adrenal (HPA) axis (Nieman et al., 2008). Neonatal respiratory distress syndrome (RDS) is most commonly a complication seen in premature infants. The condition makes it difficult to breathe. Most cases of RDS occur in babies born before 37 weeks. The less the lungs are developed, the higher the chance of RDS after birth. The problem is uncommon in babies born full-term (at 40 weeks) (Cole, 2006). Neonatal RDS occurs in infants whose lungs have not yet fully developed. The disease is mainly caused by a lack of a slippery substance in the lungs called surfactant. This substance helps the lungs fill with air and keeps the air sacs from deflating. This substance normally appears in mature lungs. It can also be due to genetic problems with lung development (Cloherty et al., 2003). Cortisol has a very important role in helping the body respond to stress.Its main effect in response to acute illness include maintenance of cell metabolism by redistributing glucose, increasing blood sugar through gluconeogenesis, aiding in the metabolism of fat, protein and carbohydrate. In addition to maintenance of blood pressure by regulating salt clearance and vasomotor tone and compartmentalization of inflammation by inhibiting circulating pro-inflammatory mediators and migration of inflammatory cells (Hoehn and Marieb, 2010). In this study the relationship between RDS and cord blood levels of ACTH and cortisol was studied in the preterm neonates with gestational ages ranging from 30 to 35 weeks and with birth weight ranging from 1 to 3.300 kg. They were divided into two groups according to presence or absence of RDS (patients group and control group).Patients group was divided into two groups according to severity of RDS. Any neonate with a congenital anomaly was excluded. It was found that there was highly significant relationship between RDS and cord blood levels of ACTH and cortisol. Preterm neonates with RDS had higher ACTH and cortisol levels than healthy preterm neonates. Also among patients group ventilated preterm neonates showed higher ACTH and cortisol levels than non-ventilated preterm neonates.

ACTH level was found to be superior to cortisol level as a screening test for RDS. In addition it was found that there are many other factors that can affect levels of ACTH and cortisol hormones in patients group.One of these factors was gender of the patients. ACTH and cortisol levels were higher in female patients than in male patients. Other factor was gestational age of the patients as there was positive significant correlation between gestational age, ACTH and cortisol levels. On the other hand, correlation between birth weight, ACTH and cortisol levels in patients group was statistically non-significant. Meanwhile, comparison between preterm neonates from singleton and multiple pregnancies was not valid due to limited number of study cases. Moreover, ACTH and cortisol levels were higher in preterm neonates born by vaginal delivery than those born by caesarean section among patients group. Furthermore, preterm neonates born by prolonged vaginal delivery showed higher levels of ACTH and cortisol than those born by spontaneous vaginal delivery among patients group. In addition there was positive significant correlation between ACTH and cortisol levels, systolic, diastolic blood pressure and heart rate. Meanwhile correlation with temperature was non-significant. On the contrary, this study showed negative significant correlation between ACTH and cortisol levels and hemoglobin and hematocrit values in patients group . So, in conclusion, the preterm infants are able to produce enough cortisol to counteract stress. Respiratory distress syndrome and mechanical ventilation are stressful conditions and are associated with high ACTH and cortisol levels. Severity of RDS and mechanical ventilation were also related to cord blood ACTH and cortisol levels of preterm neonates. This relationship could be a result of severe stress associated with positive-pressure ventilation with functioning of HPA axis and the maturation of adrenal gland in these infants.