title: The orderliness of the growth hormone (GH) release process and the mean mass of GH secreted per burst are highly conserved in individual men on successive days.
abstract: Endocrine glands signal their remote target tissues via physiologically pulsatile release of regulatory molecules. A cardinal assumption of most pathophysiological experiments is that discrete attributes of pulsatile hormone secretion are stable over successive untreated observation intervals; i.e. repeated measurements show serial within-subject reproducibility. To test this hypothesis in the GH axis, we sampled blood every 10 min for 48 h in 14 healthy men (age range, 29-77 yr; body mass index, 21-51 kg/m2). The 2 consecutive 24-h serum profiles were subjected to ultrasensitive GH chemiluminescence assay (sensitivity, 0.002 micrograms/L) with a new dose-dependent variance model to estimate within-assay precision. We then applied deconvolution analysis to estimate the number, mass, amplitude, and duration of underlying GH secretory bursts as well as simultaneously calculate the apparent GH half-life and any concurrent basal hormone secretion. Test-retest consistency was assessed by the Pearson correlation coefficient, and differences were determined by paired nonparametric (Wilcoxon) testing. Comparing successive 24-h profiles, no significant differences existed in any of the foregoing secretion or half-life measures or in a novel estimate of the relative disorderliness of hormone release, namely approximate entropy. Correlation was minimal for secretory burst amplitude and half-duration. In contrast, the calculated mean mass of GH secreted per burst was highly conserved across sessions within subjects, with an r value of 0.932 (P < 10(-6). This correlation equaled or exceeded that of mean and integrated serum GH concentrations on consecutive days (r = 0.920; P = 0.00003). The calculated daily GH production rate was also strongly reproduced (r = 0.784; P = 0.0009). Moreover, the within-subject GH half-life and GH secretory burst frequency estimates were well correlated on successive days (P = 0.034-0.004; r = 0.568-0.711). Approximate entropy values were consistent at r = 0.837 (P = 0.0019). In addition, basal GH secretion rates correlated at r = 0.622 (P = 0.0176). We conclude that homeostatic control mechanisms within the GH-insulin-like growth factor I axis strongly preserve the day to day mean mass of GH secreted per burst and the serial orderliness of the GH release process in individual healthy men across a wide span of ages and body compositions.
authors.affiliation: Department of Medical Specialties, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
authors.forename: K
authors.initials: K
authors.lastname: Friend
authors.forename: A
authors.initials: A
authors.lastname: Iranmanesh
authors.forename: J D
authors.initials: JD
authors.lastname: Veldhuis
mesh_terms: D000328:Adult; D000368:Aged; D002940:Circadian Rhythm; D006207:Half-Life; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010507:Periodicity; D015203:Reproducibility of Results
chemical_list: D019382:Human Growth Hormone