Spontaneous growth hormone secretion in healthy prepubertal children of normal stature

To evaluate the dynamics of growth hormone (GH) secretion in healthy prepubertal children of normal stature, we determined spontaneous GH secretion by measuring GH every 30 min in 21 Japanese subjects, age: 5.4±2.3 (1.6~10.6) years; height: -1.4±1.1 (- 1.98~ 1.77) SD. The 24-h mean GH concentration was 4.8±1.5 ng/ml. The 24-h mean GH was similar in boys and girls (mean±SD: 4.8±1.7 vs 4.7±1.1 ng/ml). No correlation was found between chronological age and the 24-h mean GH. The 24-h mean GH was closely correlated with GH pulse amplitude (r = 0.94; P<0.001), but not with the number of GH pulses. The 24-h mean GH was also highly correlated with 3-h mean GH after sleep and 3-h peak GH after sleep (r = 0.86; P<0.001 and r = 0.72; P<0.001, respectively). Our data suggest that in healthy prepubertal children of normal stature, (1) spontaneous GH secretion is independent of sex and age. (2) the amount of spontaneous GH secretion is controlled by pulse amplitude, not by number of pulses. (3) 3-h mean GH and 3-h peak GH after sleep might represent 24-h total spontaneous GH secretion.