Effect of Testosterone on Somatomedin-C Concentrations in Prepubertal Boys*

Abstract

To investigate the role of testosterone (T) in the pubertal elevation of somatomedin-C (SmC), six prepubertal GH-deficient boys were each given 7-day courses of GH alone (0.05 U/kg X day, im), T alone (T propionate; 25 mg/day, im), and a combination of GH and T at the same dosages. Plasma SmC levels were determined on samples drawn at the start and finish of each period, and each course was separated by a 7-day period. SmC was also measured before and after a course of T propionate (25 mg/day, im) in four GH-sufficient boys with delayed adolescence. In the GH-deficient boys, GH and the combination of GH and T resulted in comparable and significant increments of SmC (mean change, 0.68 U/ml after GH and 0.63 U/ml after the combination of GH and T). T alone caused no change in SmC in the GH-deficient boys (mean change, 0.09 U/ml), but resulted in increases in all four GH-sufficient subjects (mean change, 1.29 U/ml). In a single subject with constitutionally delayed puberty, the integrated 24-h GH concentration rose from 2.8 ng/ml before to 5.8 ng/ml after T therapy. Both the number and amplitude of GH secretory events were greater after therapy. These data show that T stimulates SmC production in prepubertal boys who can secrete GH, but not in those who are GH deficient. We postulate that the effect of T in this regard is due to its effect on pituitary GH secretion. Although the T levels were within the pharmacological range, physiological levels of T (e.g. at puberty) may be responsible for the adolescent SmC increment in men.

Time Series Analysis of Plasma Insulin-like Growth Factor-I and Gonadal Steroids in Adolescent lapanese Macaques (Macaca fuscata).

“…Wilson reported that gonadal steroids including testosterone have increased IGF-1 levels in the prepubertal female rhesus macaque [14]. It has also been reported that testosterone stimulates IGF-1 production in prepubertal boys capable of secreting GH [27]. These results clearly indicate that testosterone controls plasma IGF-1 levels in adolescent males.…”

GH as a co-gonadotropin: the relevance of correlative changes in GH secretion and reproductive state

“…Moreover, the induction of puberty by exogenous androgen or GnRH induces high-amplitude GH secretion (Blizzard et al 1989, Foster et al 1989. Very small doses of testosterone, similar to those observed in early puberty, are sufficient to increase GH pulse amplitude (Guistina et al 1997), GHRH-induced GH release (Mauras et al 1989a) and circulating IGF-I levels (Parker et al 1984). The increase in IGF-I is due to GH rather than direct effects of testosterone, since IGF-I is increased by co-administration of GH and testosterone but not by testosterone alone in GH-deficient boys (Parker et al 1984).…”

“…Very small doses of testosterone, similar to those observed in early puberty, are sufficient to increase GH pulse amplitude (Guistina et al 1997), GHRH-induced GH release (Mauras et al 1989a) and circulating IGF-I levels (Parker et al 1984). The increase in IGF-I is due to GH rather than direct effects of testosterone, since IGF-I is increased by co-administration of GH and testosterone but not by testosterone alone in GH-deficient boys (Parker et al 1984). The influence of testosterone on GH secretion is also illustrated by the ability of exogenous testosterone to correct deficient basal and GHRH-stimulated GH secretion in boys with gonadal dysfunction (Link et al 1986, Mauras et al 1989a.…”

The aromatase inhibitor letrozole increases epiphyseal growth plate height and tibial length in peripubertal male mice

“…Estrogen stimulates the release of GH from the pituitary, thereby increasing serum IGF-I levels. Testosterone also stimulates GH release in the pituitary via its local aromatization to estrogen (Parker et al 1984). However, the sex steroids may also exert a direct GH-independent effect on skeletal growth.…”