OBJECTIVE We investigated the effect of low dose cranial irradiation (18–24 Gy) on spontaneous ACTH and Cortisol secretion in children.
DESIGN We analysed 24-hour plasma ACTH and Cortisol profiles sampled at 20-minute intervals.
PATIENTS Twenty long-term survivors of acute lymphoblastic leukaemia were studied and results compared with those in 14 normal children.
MEASUREMENTS ACTH and Cortisol profiles were analysed by Fourier transformation and spectral analysis of stationarized data, autocorrelation and coherency analysis.
RESULTS The normal circadian rhythms of ACTH and Cortisol were preserved in the children after cranial irradiation. The median 0900 h and midnight values were 1 50 (0 8–6 4)pmol/l and 1 0(0 6–3–7)pmol/l respectively for ACTH and 282(48–1913) nmol/l and 57 5(44–637)nmol/l respectively for Cortisol, and were not significantly different from those in the normal group. Fourier transformation revealed dominant periodicities for ACTH at 0–7–11 h, equivalent to 22–34 ACTH secretory bursts per 24 hours, and for Cortisol at 0 7–11 h and 2–4 8 h. Similar results were found in the normal group.
Coherency analysis indicated a significant shared periodicity of 0 7–1 2 h in nine children, corresponding to 20–34 related secretory bursts in 24 hours for ACTH and Cortisol. After pooling the coherency spectra in the cranially irradiated group, comparison with the pooled data from the normal group revealed no significant difference between the two groups in the relationship between the two hormones.
CONCLUSION No significant disruption of spontaneous ACTH or Cortisol secretion, either in the amount or pattern of hormones secreted, was found in children after low dose cranial irradiation (18–24 Gy).