THE PITUITARY-ADRENAL RESPONSES TO EXOGENOUS HUMAN CORTICOTROPIN-RELEASING HORMONE IN PRETERM, VERY-LOW-BIRTH-WEIGHT INFANTS

To evaluate the pituitary-adrenal reserve and to standardize the metho dology of performing the human CRH (hCRH) stimulation test, we perform ed the hCRH test on 14 preterm (<32 gestational weeks), very low birth weight infants, who did not receive antenatal or postnatal corticoste roid treatment, on days 7 and 14 of life. Blood samples were obtained 0 (baseline), 15, 30, and 60 min after an iv dose of hCRH (1 mu g/kg). The plasma ACTH concentration rose from a basal value of 5.7 +/- 0.6 pmol/L (mean +/- SEM) to 11.9 +/- 2.1 pmol/L (P < 0.005), 9.2 +/- 1.2 pmol/L (P < 0.005), and 7.7 +/- 0.8 pmol/L (P < 0.005) at 15, 30, and 60 min, respectively. The corresponding rises in serum cortisol fi om a basal concentration of 396 +/- 67 nmol/L were 509 +/- 71 nmol/L (P < 0.0001), 647 +/- 62 nmol/L (P < 0.0001), and 578 +/- 60 nmol/L (P < 0 .0001). The plasma ACTH concentration consistently peaked early at 15 min; whereas the maximum cortisol response occurred 30 min post-hCRH s timulation. No significant differences were detected between the hCRH tests performed on days 7 and 14 (P > 0.15). Mechanical ventilation, i nfant gender, and mode of delivery did not significantly influence the hormonal responses (P > 0.25). We have defined in this study the patt ern, the magnitude of the pituitary-adrenal response, and the timing o f the peak concentrations of plasma ACTH and serum cortisol in relatio n to a standard iv dose of hCRH. The hCRH test in very low birth weigh t infants appears to be safe and reproducible, and produces a pituitar y-adrenal response comparable to that seen in older children and adult s, indicating that pituitary-adrenal function is mature at these early stages of gestation.