Contemporary tools for the analysis of episodic growth hormone secretion and clearance in vivo

The evaluation of episodic GH release is made difficult by the apparently random nature of GH secretory bursts, the frequent occurrence of minimally detectable plasma GH concentrations, the relatively rapid plasma disappearance rate of endogenous GH, and the large number of metabolic and environmental cues that alter GH dynamics. Nonetheless, the development of objective, statistically based, and reproducible computerized algorithms to quantify episodic GH release has offered new insights into the pathophysiological regulation of GH secretion in health and disease. Moreover, the recent formulation of algebraically explicit biophysical models of GH secretion and clearance has made possible a complete quantitative description of GH secretory and clearance dynamics over a full 24 hours of observation. Such analytical tools allow investigators to enumerate with statistically bounded confidence limits the number, amplitude, durations, and temporal locations of all significant underlying secretory bursts and simultaneously calculate the half-life of endogenous GH disappearance from all GH concentrations and their variances considered together. Accordingly, in conjunction with contemporary refinements in GH assay techniques, such novel approaches to dissecting the temporal structure of GH secretion and clearance in vivo should result in significantly enhanced understanding of GH dynamics in health and disease.