Properties of spontaneous growth hormone secretory bursts and half-life of endogenous growth hormone in boys with idiopathic short stature

We analyzed endogenous GH secretory dynamics and MCRs by a novel quantitative deconvolution technique in 20 boys with idiopathic short stature (ISS) and 35 boys of normal stature in Tanner stage I of puberty. We tested the null hypotheses that 1) ISS is not associated with any alterations in the frequency, mass, amplitude, or duration of spontaneous GH secretory bursts and/or the 24-h GH production rate; and 2) the half-life of endogenous GH is not altered in ISS. The boys with ISS had a mean (±SEM) bone age of 8.0 ± 0.42 yr and a chronological age of 10 ± 0.50 yr. The latter was similar to the chronological (and bone) age of the normal boys of 9.8 ± 0.23 (and 9.3 ± 0.34) yr. Mean height SD scores were significantly lower in ISS boys, viz. -2.7 ± 0.15 in ISS vs. +0.34 ± 0.13 in normal boys (P < 0.001). Plasma insulin-like growth factor-I concentrations were similar in the two groups, as were (24-h) mean serum GH concentrations, viz. 3.5 ± 0.29 μg/L in ISS and 4.1 ± 0.49 μg/L in normal boys (P = NS). Deconvolution analysis revealed that the mean number of GH secretory events per 24 h was similar in normal and ISS boys, viz. 9.6 ± 0.76 (normal) vs. 8.4 ± 0.55 (ISS), and that there was no significant difference in mean GH interburst intervals. The amplitude, mass, and duration of computer-resolved GH secretory bursts also did not differ in normal and ISS boys. The half-lives of endogenous GH were estimated to be 16 ± 0.77 min in the ISS and 18 ± 0.93 min in the control boys (P = NS). The calculated daily GH secretion rate per unit distribution volume was not significantly reduced in ISS, i.e. 194 ± 19 μg/L-day in ISS vs. 177 ± 19 μg/L·day in control boys. Moreover, daily GH secretion rates corrected for body mass index (weight/height²) in the twp groups were not significantly different. In summary, the present cohort of boys with ISS manifested no significant alterations in GH secretory burst frequency, duration, mass, or amplitude or in the half-life of endogenous GH compared to normal boys in Tanner stage I of pubertal development. Indeed, whether daily GH secretion rates are expressed per unit distribution volume or per unit body mass index, groups of boys with ISS and normal height controls secrete similar total amounts of GH. We conclude that the overall dynamics of GH secretion and clearance in boys with ISS considered as a whole cannot be distinguished readily from physiological patterns observed in prepubertal boys of normal height.