Nocturnal serum growth hormone concentration is not augmented by short-term testosterone infusion in pubertal boys

Changes in serum immunoreactive and bioactive growth hormone concentrations in boys with advancing puberty and in response to a 20-hour estradiol infusion

Acceleration of linear growth during puberty is associated with increased GH secretion, although the relationship between growth and GH is complex. As GH exists as a family of isoforms, some of which may not be identified by immunoassay, there may be alterations in isoform secretion during pubertal maturation that result in increased growth. The changes in serum immunoreactive and bioactive GH concentrations across pubertal maturation were determined in 30 boys, aged 6.5-19.3 yr, with idiopathic short stature or constitutional delay of adolescence. Data were grouped as follows: 1) 6 prepubertal boys with bone age 7 yr or less; 2) 5 prepubertal boys with bone age of more than 7 yr, 3) 10 boys in early puberty; 4) 9 boys with mid- to late puberty. Blood was obtained every 20 min from 2000-0800 h. An equal aliquot of each serum sample was pooled for determination of GH by bio- and immunoassays. The mean serum immunoreactive GH concentration increased from 2.1 +/- 0.3, 1.8 +/- 0.3, and 2.9 +/- 0.5 micrograms/L in groups 1, 2, and 3, respectively, to a peak of 4.6 +/- 0.7 micrograms/L in group 4 (P < 0.05 vs. groups 1-3). The mean serum GH bioactivity was 48 +/- 13 micrograms/L in group 1 and declined to 39 +/- 8 and 31 +/- 3 micrograms/L in groups 2 and 3, increasing to a maximum of 64 +/- 15 micrograms/L in group 4 (P < 0.05 vs. group 3). The ratio of bioactive to immunoreactive GH suggests that the biopotencies of secreted isoforms do not increase during pubertal maturation. The role of E2 in increasing GH secretion was characterized in 8 additional early pubertal boys. Each boy received a saline infusion from 1000-0800 h, followed 1 week later by an infusion of E2 at 4.6 nmol/m2.h. Blood was obtained every 15 min from 2200-0800 h for GH and LH and every 60 min for E2 and testosterone. An equal aliquot of each overnight serum sample was pooled for insulin-like growth factor I (IGF-I) and GH by immuno- and bioassays. The mean serum LH concentration decreased from 5.0 +/- 0.9 to 2.3 +/- 0.6 IU/L (P < 0.01), and the E2 concentration increased from 22 +/- 4 to 81 +/- 26 pmol/L (P < 0.01) during saline and E2 infusions, respectively. Mean serum GH concentrations as measured by immunoassay were similar during both infusions (6.6 +/- 1.4 vs. 9.7 +/- 2.1 micrograms/L; saline vs. E2 infusion, respectively). In contrast, the mean serum GH concentration, as measured by bioassay, decreased from 48 +/- 10 micrograms/L during saline infusion to 16 +/- 3 micrograms/L during E2 infusion (P < 0.05). The mean serum IGF-I concentration also decreased significantly from 116 +/- 17 to 93 +/- 15 micrograms/L (saline vs. E2 infusion, respectively; P < 0.05). Thus, although mean overnight serum GH concentrations increase in late puberty, whether measured by immuno- or bioassay, an acute increase in E2 produces an acute decline in serum GH bioactivity and a lesser decline in the serum IGF-I concentration. These unexpected changes indicate that E2 may affect pubertal growth and GH secretion in a complex or biphasic manner depending on the context in which it is administered.

Gonadal steroid hormone regulation of the somatotropic axis during puberty in humans Mechanisms of androgen and estrogen action

The adolescent growth spurt is associated with a sex steroid hormone-dependent rise in GH production; both androgens and estrogens are implicated as positive regulators of the somatotropic axis during puberty. The issue is complicated by the fact that testosterone may act both directly via the androgen receptor and indirectly, after its aromatization to 17beta-estradiol, through the estrogen receptor. Recently, a number of investigators have studied the effects of the administration of androgen and estrogen receptor antagonists, as well as nonaromatizable androgens, on GH secretion. These reports suggest that estrogen receptor-dependent processes play a facilitatory role in the pubertyassociated rise in GH secretion. If androgen receptor-mediated events are involved in the control of the somatotropic axis, their role is likely inhibitory. A hypothalamic site of action of the sex steroids is postulated.

The effects of oxandrolone on the growth hormone and gonadal axes in boys with constitutional delay of growth and puberty

OBJECTIVE

We studied the effects of oxandrolone on serum concentrations of LH, FSH, testosterone, GH, SHBG, DHEAS, IGF-I and insulin in boys with constitutional delay of growth and puberty.

DESIGN

Ten boys with constitutional delay of growth and puberty, mean age 13.8 years (range 12.4-15.5) were studied. Twenty-four-hour serum concentration profiles of GH, LH and FSH were constructed by drawing blood samples at 20-minute intervals. Three study occasions over a period of 6 months were chosen to assess hormone concentrations before, during and 6 weeks after a 3-month course of oxandrolone (2.5 mg once daily) therapy.

RESULTS

Growth velocity increased during oxandrolone treatment and stayed higher after therapy (pre 3.9 +/- 0.5; on 6.3 +/- 0.8; post 6.4 +/- 0.9 cm/year (mean +/- SEM) two way ANOVA, F = 5.3, P = 0.02). Oxandrolone had androgenic effects, suppressing mean serum LH concentrations from 1.7 +/- 0.3 to 1.1 +/- 0.2 U/I and serum testosterone concentrations from 1.9 +/- 0.6 to 0.8 +/- 0.1 nmol/l. SHBG concentrations were also reduced from 130.9 +/- 14.6 to 30.7 +/- 7.3 nmol/l. Serum GH concentration fell slightly from 5.9 +/- 0.6 to 4.8 +/- 0.5 mU/l. After cessation of treatment, there was a significant 'rebound' in mean 24-hour serum LH (2.6 U/l +/- 0.4) and testosterone concentrations (3.2 +/- 0.9 nmol/l) but no change in serum GH concentrations. SHBG values also rose but not to the same extent as those observed before therapy (82.0 +/- 8.4 nmol/l). There were no statistically significant differences in serum concentrations of FSH, DHEAS, IGF-I and insulin over the study period. In a stepwise multiple regression analysis of factors that might influence the growth rate observed, the 24-hour mean serum testosterone concentration and the treatment (on or off) with oxandrolone were the main influences. The relationship was described by the equation Height velocity = 0.69 (24-hour mean serum testosterone concentration)+1.70 (treatment regimen)+3.37 (adjusted R2 = 0.35, F = 8.39, P = 0.001).

CONCLUSIONS

Oxandrolone has an androgenic action as shown by changes in serum LH, testosterone and SHBG concentrations and by the lack of effect on FSH. No effect of oxandrolone on the GH axis was documented. We suggest that the growth promoting effects of oxandrolone are related in part to the mild androgenic effects of the steroid and the growth acceleration following oxandrolone withdrawal may reflect increasing total serum testosterone concentrations and decreasing levels of SHBG and progress in puberty.