Endocrine glands signal their remote target tissues via physiologically pulsatile hormone release. 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 widely held hypothesis, we sampled blood every 10 min for 48 h in 14 healthy men (age range 29 -77, body mass index 21-51). The two consecutive 24-h profiles were subjected to ultrasensitive GH chemiluminescence assay (sensitivity 0.002 ug/L) with a new dosedependent variance model to estimate within-assay precision (Meth. Enzym. 240:121,1994), followed by deconvolution analysis in order to estimate the number, mass, and duration of underlying GH secretory bursts, as well as simultaneously calculate the apparent GH half-life and any concurrent basal hormone secretion (PNAS 84:7686, 1987). Test-retest consistency was assessed by the Pearson correlation coefficient, and by paired non-parametric (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 relative disorderiiness of hormone release, namely approximate entropy (ApEn, PNAS 88:2297,1991). Correlation was minimal for mean secretory burst amplitude or half-duration. In contrast, the calculated 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 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 within-subject GH half-life and burst frequency estimates were correlated on successive days (P values 0.034 to 0.004, R=+0.568 to + 0.711). ApEn values correlated 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-IGF-I axis strongly preserve the day-to-day mass of GH secreted per burst and the serial orderliness of the GH release process in individual healthy humans across a wide span of ages and body compositions.
|Original language||English (US)|
|Journal||Journal of Investigative Medicine|
|State||Published - 1996|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)