Analyses of 24-Hour Growth Hormone Profiles in Children: Relation to Growth*

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Abstract
The relationship between height and amount of GH measured during a 24-h period was studied in 127 children who were growing at different rates. Of the children, 88 were prepubertal (3-16 yr old) and 39 were pubertal (10-16 yr old). The height of each child was expressed as the SD score, i.e. height in relation to the sex-and age-matched Swedish reference groups, and spontaneous GH secretion was estimated by taking integrated 20-min blood samples for a 24-h period, i.e. 72 samples/child. In a few children, discrete samples were taken in parallel with the integrated 20-min samples with virtually the same results. Plasma GH was estimated in each sample using a polyclonal RIA method. To compare different 24-h GH profiles, the profiles were analyzed using a computer program (Pulsar). One objective of the study was to determine if less frequent sampling and/or shorter sampling periods yielded the same information as that obtained by 20-min sampling for the whole 24-h period. To determine if less frequent sampling provided the same information as that obtained by the 20-min period, we simulated 40-and 60-min periods by pooling two or three consecutive samples. No difference was found between 20-and 40-min sampling, but with 60-min sampling the mean calculated baseline plasma GH concentrations increased, and the GH concentration within peaks [the area under the curve above the baseline (AUCb)] decreased markedly. A 30-min sampling interval thus seems to be a valid practical compromise. To determine if sampling periods shorter than 24 h provided the same information, we divided the profiles, which started at 0900 h, into two 12-h, three 8-h and four 6-h periods. A graded decrease in AUCb and a corresponding increase in the baseline was found with the shorter periods, indicating that the whole 24-h period is necessary for GH sampling. Another objective of the study was to determine whether there was a correlation between 24-h GH secretion and the height, age, and sex of the children. In the prepubertal children, the height (in SD scores) was highly correlated (r = 0.69; P < 0.001) with GH AUCb during the 24-h period. Height also correlated with AUCb estimated over shorter time periods; the correlation diminished with decreasing time. In the pubertal children, an nonlinear correlation (r = 0.36; P < 0.05) was found between height and 24-h GH (AUCb). Among the prepubertal children no correlation was found with sex or age and 24-h GH secretion. We conclude that there is a relationship between 24-h GH secretion and the growth of normal children over a wide range of growth rates.