Circadian variation of plasma cortisol in prepubertal children with normalstature, short stature and growth hormone deficiency

OBJECTIVES When studying the relationship between spontaneous secretion of growth hormone (GH) and cortisol in children, most studies show no correlat ion in mean levels of these two hormones, while others found positive or ev en strongly negative correlations. These contradictory results could be par tly due to the inability to properly compare hormones that are characterize d by circadian and ultradian variations in their secretory profiles. We aim here to study possible differences in rhythm characteristics of plasma cor tisol with stature and to compare the circadian secretory patterns of corti sol and GH, PATIENTS We analysed data from 135 prepubertal children: (1) 14 GH-deficien t children; (2) 36 children with short stature (2-3 SD below their peer gro up mean); (3) 57 children with very short stature (3-4 SD below their peer group mean); and (4) a reference group of 28 children with normal stature ( +/- 2 SD), Subjects were living in a hospital setting on a diurnal waking ( 07.30-22.30 h), nocturnal resting routine during sampling, consuming the us ual hospital diet at fixed times. MEASUREMENTS Cortisol and GH concentrations were determined by radioimmunoa ssay in plasma obtained at about 2-3 h intervals during most of the day and at half-hour intervals between 22.00 and 02.00 h. Circadian rhythm charact eristics obtained by least-squares estimation were compared between groups divided according to gender and stature with a parameter test. RESULTS show a statistically significant circadian rhythm in cortisol secre tion for all groups studied (P<0.001 in all cases). A comparison of circadi an parameters indicated similar characteristics between subjects of short, very short and normal stature. Despite a borderline statistically significa nt difference in rhythm-adjusted mean and amplitude of GH between nondefici ent and GH-deficient children, there was no difference in the circadian pat tern of cortisol secretion between these two groups. No correlation was fou nd in circadian mean, amplitude, average, standard deviation, standard erro r, minimum or maximum between GH and cortisol for any of the groups of chil dren. CONCLUSIONS Any possible relation between GH and cortisol remains unclear. Moreover, GH-deficient children are not necessarily characterized by either hyper- or hypocortisolaemia.