Females secrete growth hormone with more process irregularity than males in both humans and rats

Abstract

In humans, serum growth hormone (GH) concentrations are significantly higher in women than in men, but the neuroendocrine mechanisms that underlie such gender differences are not known. We compared normal episodic GH secretion in males and females in three distinct settings: two human studies employing quite different assay techniques (immunoradiometric assay and a high-sensitivity immunofluorimetric method) and a rat study. To quantify the amount of regularity in data, we utilized approximate entropy (ApEn), a scale- and model-independent statistic. In each study, females exhibited significantly greater statistical irregularity in GH concentration series than their male counterparts (P < 10(-3) for each human study, P < 10(-6) for the rat study), implying that mass and mode of GH secretion are regulated differently in males and females. The regularity comparisons indicated complete gender separation (100% specificity and sensitivity) for the rat study and nearly complete separation for the immunofluorimetric assay study. The consistency and statistical significance of these findings suggest that this gender difference may be broadly based within higher animals and that this may be readily evaluated objectively by analysis of ApEn.

Exploring endocrine GH pattern in mice using rank plot analysis and random blood samples

“…Rank plot analysis provides a useful readout of pulsatile GH Pincus et al (1996) explored pulsatile GH in cannulated rats as time series (Fig. 1A and B), revealing sexual dimorphism in GH secretion.…”

“…We therefore constructed six pulsatile profiles ( Fig. 2A and B), representing the different types of GH secretion patterns as they can be observed due to disease, gene mutation, or aging (Pincus et al 1996, Kappeler et al 2004 and data herein). We then transformed these six time series into rank plots, by taking one data point every 5 min and arranging them by magnitude ( Fig.…”

“…the second session at 0840, 1040, 1240 h, etc. and show typical individual 24 h GH profiles of one male and one female rat, taken from Pincus et al (1996). The first 600 min correspond to the dark period, and 600-1440 min to the light period.…”

“…Rank plot data were then submitted to statistical analysis. To validate this protocol, we transformed the published data on pulsatile GH in rats (Pincus et al 1996) from serial to rank plot. We also showed that rank plot efficiently reveals the key features of various simulated pulsatile GH profiles.…”

The Obestatin/Ghrelin System as a Novel Regulatory Mechanism of Iris Muscle Contraction

“…It is currently believed that HF is related to the parasympathetic system, while the LF is associated also with the sympathetic activity (Task Force 1996). The nonlinear indices considered in this study, ApEn and SampEn, which have broadly been applied in human heart-rate signal analysis, had also been shown to be useful as a measure of regularity in experiments on rats (Pincus et al 1996), although with much less application in this field. For approximate entropy (Pincus and Viscarello 1992), ApEn(m, r), and Sample Entropy (Richman and Moorman 2000), SampEn(m, r), which are nonlinear measures obtained through direct signal estimation, capable of quantifying signal complexity (or irregularity) robustly with short segments, the parameter m is the embedding dimension and the parameter r acts as a threshold.…”