24-hour secretion of growth hormone (GH), insulin-like growth factors-I and -II (IGF-I, -II), prolactin (PRL) and thyrotropin (TSH) in young adults of normal and tall stature.

Abstract

Studies of the growth hormone (GH) secretory dynamics of children with normal and idiopathic short stature (ISS) have revealed that the regulation of the GH-somatomedin (GHS) axis can differ significantly among normal individuals. Information on the GH secretion in idiopathic tall stature (ITS) is scarce. We previously showed that the GH response to stimulation with GH-releasing hormone (GHRH) in male, late adolescents and young adults with ITS is significantly greater than that of their sex and age-matched controls of average height. In the present study, we studied the 24-hour (hr) GH, insulin-like growth factor-I and -II (IGF-I and -II), prolactin (PRL) and thyroid-stimulating hormone (TSH) secretion by every 30 minutes (min) sampling in 12 young, healthy male Greek army recruits. Group I [n = 6, age 22 + 1.4 years (y.), mean + standard deviation (SD)] had a height of 198.5 + 4.2cm, at least 3 SD's above the mean of the Greek male population. Group II (n = 6, age 20.5 + 1.05 y.) had a height of 169.2 + 3.4cm, within 2SD's of the normal mean. Serum IGF-I levels were determined in both unextracted and extracted samples. Our results indicated that the number of secretory bursts and the circadian panel of GH, IGF-I and -II, PRL and TSH were similar in the two groups. Both the amplitude of the secretory GH peaks (5.08 + 3.07 vs. 3.3 + 0.8 ng/ml, p = 0.19,) and the area under the curve (AUC) of the 24-hour GH secretion (9.8 + 5.5 vs. 6.6 + 1.3 ng/ml/hr, p = 0.2) were higher in group I than in group II, but the difference was not significant. A significant nocturnal increase of both IGF-I and -II levels was found only in extracted human plasma (p < 0.001), whereas measurements of IGF-I in unextracted samples failed to reveal circadian variation (p < 0.1). We conclude that no significant differences were found in this pilot study of the neurosecretory regulation of the GHS axis between individuals of tall and normal stature. A tendency for greater amount of GH secretion per secretory peak was found in persons with tall stature; however, this finding needs to be confirmed in a larger study. IGF-I and -II levels had a significant circadian variation with a large nocturnal surge, when measured in extracted plasma. The latter, might be explained by circadian variation of the circulating IGF-binding proteins and its detection appears to be method of extraction-dependent.

Circulating levels of insulin-like growth factor-1 and insulin-like growth factor binding protein-3 in patients with severe head injury

“…The circulating level of both IGF-1 and IGFBP-3 varied widely and without any trend, indicating that the level of these analytes in blood does not remain constant. Stratakis, Mastorakos and Magiakou 43 measured the level of IGF-1 and IGF-2 in young adults of normal and tall stature and found that they had large circadian variation with a nocturnal surge, when measured in "acid-ethanol extracted" plasma. They found that measurements of IGF-1 in "unextracted" samples failed to reveal the same circadian variation in any of the subjects studied.…”

Gigantism

“…Potential confusion may arise when evaluating normal adolescents because significantly higher IGF-I levels occur during puberty than in adulthood (40), a fact that emphasizes the importance of using age-referenced norms. Although higher concentrations of IGF-I have been reported in children and adolescents with constitutional tall stature (41), no significant differences in neurosecretory dynamics of the GH-IGF-I axis have been found in healthy young adults with heights of more than three sd above the mean as compared with controls (42). The gold standard for making the diagnosis of GH excess is a failure to suppress serum GH levels to less than 5 ng/dL after a 1.75 gm/kg oral glucose challenge (maximum, 75 g).…”

Correlation between Circadian Gene Variants and Serum Levels of Sex Steroids and Insulin-like Growth Factor-I

“…IGF-I is secreted primarily by the liver and is mostly bound by IGFBP3. Some but not all previous studies have shown that serum levels of IGF-I and IGFBP3 vary throughout the day in a circadian rhythm (24)(25)(26)(27)(28)(29). In men with hypopituitarism, growth hormone treatment not only increased gene expression of IGF-I but also increased CLOCK expression and decreased PER1 expression in muscle cells (30).…”