Do IGF-I concentrations better reflect growth hormone (GH) action in children with short stature than the results of GH stimulating tests? Evidence from the simultaneous assessment of thyroid function

Thyroid function in children with short stature accompanied by isolated pituitary hypoplasia

PURPOSE

Few studies have focused on thyroid function in children with isolated pituitary hypoplasia (IPH). The purpose of this study was to investigate thyroid function in children with short stature accompanied by IPH and evaluate the values of thyroid function for the diagnosis of IPH.

METHODS

This was a retrospective observational study. A total of 100 children with short stature accompanied by IPH were enrolled. Among them, 68 children presenting with isolated growth hormone deficiency (IGHD) were chosen as the IPH group. Sixty-eight age-matched and sex-matched IGHD children without pituitary abnormalities were chosen as the control group. Clinical, hormonal, and imaging parameters were analyzed. The diagnostic value of thyroid function for IGHD children with IPH was evaluated.

RESULTS

Children in the IPH group had significantly lower height standard deviation score (HSDS), HSDS-target height standard deviation score (THSDS), free thyroxine (FT4), insulin-like growth factor-1 standard deviation score (IGF-1SDS), and pituitary height than the control subjects (p = 0.027, p = 0.033, p < 0.001, p = 0.03, and p < 0.001, respectively). The value of the area under the curve (AUC) was 0.701 (95% CI 0.614-0.788, p < 0.001) when the cut-off value for FT4 was ≤ 16.43 pmol/L and the sensitivity and specificity were 72.1 and 61.8%, respectively. FT4 levels were positively correlated with FT3, GH peak, and IGF-1 SDS levels in all children with short stature accompanied by IPH (p < 0.001, p = 0.009, and p = 0.01, respectively).

CONCLUSION

IGHD children with IPH had lower FT4 levels than IGHD children without pituitary abnormalities. FT4 levels may have diagnostic value for IGHD children with IPH.

Contribution of Ghrelin to the Pathogenesis of Growth Hormone Deficiency

In this review we described the interactions between ghrelin and the growth hormone (GH)-insulin-like growth factor 1 (IGF-1) axis in children and adults with growth hormone deficiency (GHD). A possible involvement of these interactions in the pathogenesis of unexplained cases of GHD was suggested. Current research provides more and more details to the knowledge on the circadian rhythm of ghrelin. We gathered reports on the decreasing effect of Helicobacter pylori-related chronic gastritis on the number of ghrelin immunopositive cells and the consequent decrease in ghrelin serum concentration. The gastrointestinal tract microflora modification of the ghrelin action, by the mechanism of molecular mimicry, was also stressed. Moreover, the mutual relationships between ghrelin and the TSH-FT4/FT3 axis in growth and metabolic processes are described. It is to be recalled that FT4 and FT3 exert a permissive impact on IGF-1 action and, in turn, GH, in reaction mediated by IGF-1, enhances the monodeiodination of FT4 to FT3. Finally, we discussed the latest attempts to use the GH secretagogue receptor (GHS-R) analogues for possible diagnostic and therapeutic purposes.

Strong Positive Correlation between TSH and Ghrelin in Euthyroid Non-Growth Hormone-Deficient Children with Short Stature

The growth processes in children depend on the proper functioning of some hormones and growth factors. Recently, a positive correlation between ghrelin and TSH (thyroid stimulating hormone) in patients with hyper- and hypothyroidism was proved. Moreover, in hypothyroid rats with high ghrelin concentration, growth hormone (GH) and insulin-like growth factor I (IGF-I) secretion was suppressed. We analyzed these relationships in euthyroid prepubertal children with idiopathic short stature (ISS). The analysis comprised concentration of ghrelin, GH in stimulating tests and during the night, as well as IGF-I, TSH, free thyroxine (FT4) and free triiodothyronine (FT3) in 85 children with ISS (36 girls, 49 boys) aged 9.65 ± 3.02 years (mean ± SD). A strong positive correlation between ghrelin and TSH was confirmed (r = +0.44, p < 0.05). A higher ghrelin but lower nocturnal GH and lower IGF-I were observed in children with higher normal TSH concentration than those in children with lower normal TSH. Interestingly, alterations of TSH level were without any impact on FT4 and FT3 concentrations. Summing up, in ISS prepubertal euthyroid children, ghrelin and TSH secretion are closely related. On the other hand, the higher the TSH, the lower the nocturnal GH and IGF-I levels. The contribution of the above findings in deterioration of growth processes requires further studies.

Comparison of nocturnal and morning ghrelin concentration in children with growth hormone deficiency and with idiopathic short stature

Ghrelin - a growth hormone (GH) secretagogue - presents a circadian rhythm with higher nocturnal than diurnal concentration (similar to GH). However, daily ghrelin production depends on food intake and nutritional state; it is increased in the fasting state and decreased after a meal. Since most past research concerning short stature children has relied on the morning ghrelin concentration for analyses, we decided to assess ghrelin concentration at the 60^th and 90^th minute after falling asleep and in the morning at 06:00 h, shortly after waking up from nighttime sleep (after 12 h of fasting). We compared these ghrelin concentrations to determine differences between nocturnal and morning ghrelin release in short children, both with idiopathic short stature (ISS) and growth hormone deficiency (GHD). We also analyzed the correlation between the nocturnal and morning ghrelin concentrations with nocturnal GH concentrations, measured at the same time points, as well as with maximal GH concentration, achieved by stimulation tests, and with the insulin-like growth factor I (IGF-I). The ghrelin and GH concentration 60^th and 90^th minute after falling asleep, as well as fasting morning ghrelin and IGF-I concentrations, were measured in 19 (n = 10 ISS and n = 9 GHD) prepubertal short children (7 girls and 12 boys), aged 10.36 ± 3.06 y. Differences between the nocturnal and morning ghrelin concentrations were analyzed by the Wilcoxon matched-pairs signed-rank test. Typical regression and correlation analyses were used to assess relationships among parametric data for other analyses. The Wilcoxon test showed ghrelin concentration is significantly higher in the morning than both at the 60^th and 90^th minute after falling asleep time points (in ISS and GHD). A significant correlation was observed: a) positive - between nocturnal ghrelin (both at the 60^th and 90^th minute) and morning ghrelin concentrations; b) positive - between ghrelin at the 60^th minute and nocturnal GH concentrations (both at the 60^th and 90^th minute); c) negative - between ghrelin at the 60^th minute and IGF-I concentrations; and d) negative - between body mass index and ghrelin concentrations at the 60^th and 90^th minute. We conclude: 1) in short children, both with GHD and with ISS, morning ghrelin level reflects its nocturnal concentration; however, it is significantly higher than the nocturnal ones. There is no significant difference between the measurement of ghrelin concentration at night at the 60^th or 90^th minute after falling asleep; 2) morning ghrelin concentration is affected by the hunger and satiety; therefore, it appears that nocturnal measurements better reflect the pool of hormone responsible for stimulation of GH and IGF-I secretion, especially since positive correlation between nocturnal ghrelin and nocturnal GH secretion was noted; 3) it seems that a higher body mass index is an additional independent factor, associated mainly with lower nocturnal (but not morning) ghrelin secretion.

Nutritional Status in Short Stature Children Is Related to Both Ghrelin and Insulin-like Growth Factor I Concentrations

OBJECTIVES

Ghrelin plays an important role in the growth processes in children. In addition, it regulates appetite. The aim of the study was to assess ghrelin and insulin-like growth factor type I (IGF-I) concentrations in children with idiopathic short stature, dependent on nutritional status.

METHODS

The study group included 116 children, ages 10.6 ± 3.5 years (mean ± standard deviation), with idiopathic short stature (height <-2.0 standard deviation scores [SDS], maximal growth hormone [GH] secretion during 2 GH-stimulating tests->10 ng/mL). In each child, fasting ghrelin, IGF-I, insulin-like growth factor binding protein 3 (IGFBP-3), glucose, insulin, lipids, leptin, adiponectin, and resistin concentrations were assessed. The IGF-I/IGFBP-3 molar ratio was calculated to determine the IGF-I bioavailability. According to body mass index SDS calculated for height age, the children were divided into 3 groups: poorly nourished (thin), normal, and obese. The control group consisted of 19 healthy children, ages 11.0 ± 3.5 years, with normal body weight and height.

RESULTS

Ghrelin concentration was significantly higher in short, thin children than in short, obese children (1458.3 ± 798.5 vs 917.2 ± 303.0 pg/mL; P < 0.005). In turn, IGF-I/IGFBP-3 molar ratio was significantly lower in short, thin children than in short, obese children (0.16 ± 0.06 vs 0.28 ± 0.15; P < 0.005).

CONCLUSIONS

In short, thin children, despite elevated ghrelin production, the low IGF-I concentration is observed, probably due to undernutrition and worse IGF-I formation. In short, normal-weight children and in short, obese ones, ghrelin and IGF-I production is normal, and it seems that mechanisms responsible for their short stature are other than low IGF-I.

Thyroid hormone signaling and homeostasis during aging

Studies in humans and in animal models show negative correlations between thyroid hormone (TH) levels and longevity. TH signaling is implicated in maintaining and integrating metabolic homeostasis at multiple levels, notably centrally in the hypothalamus but also in peripheral tissues. The question is thus raised of how TH signaling is modulated during aging in different tissues. Classically, TH actions on mitochondria and heat production are obvious candidates to link negative effects of TH to aging. Mitochondrial effects of excess TH include reactive oxygen species and DNA damage, 2 factors often considered as aging accelerators. Inversely, caloric restriction, which can retard aging from nematodes to primates, causes a rapid reduction of circulating TH, reducing metabolism in birds and mammals. However, many other factors could link TH to aging, and it is these potentially subtler and less explored areas that are highlighted here. For example, effects of TH on membrane composition, inflammatory responses, stem cell renewal and synchronization of physiological responses to light could each contribute to TH regulation of maintenance of homeostasis during aging. We propose the hypothesis that constraints on TH signaling at certain life stages, notably during maturity, are advantageous for optimal aging.

Decreased thyroid follicle size in dwarf mice may suggest the role of growth hormone signaling in thyroid growth regulation

Background

Altered somatotrophic signaling is among the most important potential mechanisms of extended longevity. Ames dwarf (df/df) mice are homozygous for mutation at the Prop-1 gene, leading to a lack of growth hormone (GH), prolactin and thyroid stimulating hormone (TSH). Mice homozygous for targeted disruption of the growth hormone receptor/growth hormone binding protein gene are known as GH receptor knockout (GHRKO) mice or “Laron dwarf”. Both, df/df and GHRKO mice, are characterized by reduced body size, low plasma insulin and insulin-like growth factor-I (IGF-I), remarkably extended longevity, and severe (in df/df mice) or mild (in GHRKO mice) thyroid hypofunction. Recently, by crossing df/df and GHRKO mice, double-mutant Ames dwarf/GHRKO (df/KO) mice were created. Interestingly, these mice are smaller than Ames dwarfs or GHRKOs, and also have reduced insulin and IGF-I levels. The aim of the study was to investigate if and to what extent certain thyroid morphological parameters, such as inner follicular surface area, inner follicular perimeter, as well as the follicular epithelium thickness are changed in the examined dwarf mice.

Methods

This quantification was performed in thyroids collected from df/df, GHRKO and df/KO female mice, at approximately 5–6 months of age. We used a computerized plotting programme that combines a live microscopic image of the slide with an operator-generated overlay.

Results

Inner follicular surface area and inner follicular perimeter were decreased in all examined kinds of dwarf mice as compared to normal animals. Furthermore, decreases in these two parameters were more pronounced in df/df and df/KO than in GHRKO mice. Concerning the follicular epithelium thickness, only a tendency towards decrease of this parameter was found in all three kinds of dwarf mice.

Conclusions

Parameters characterizing thyroid follicle size are decreased in all three examined models of dwarf mice, which may explain decreased thyroid hormone levels in both basal mutants (Ames dwarfs and GHRKOs). df/df mutation seems to predominate over GHRKO genetic intervention concerning their effects on thyroid growth. Beside TSH, also GH signaling seems to constitute a crucial element in the regulation of thyroid growth and, possibly, function.