High serum sex hormone-binding globulin (SHBG) and low serum non-SHBG-bound testosterone in boys with idiopathic hypopituitarism: effect of recombinant human growth hormone treatment

Does sex hormone-binding globulin cause insulin resistance during pubertal growth?

BACKGROUND

The directional influences between serum sex hormone-binding globulin (SHBG), adiposity and insulin resistance during pubertal growth remain unclear. The aim of this study was to investigate bidirectional associations between SHBG and insulin resistance (HOMA-IR) and adiposity from childhood to early adulthood.

METHODS

Participants were 396 healthy girls measured at baseline (age 11.2 years) and at 1, 2, 4 and 7.5 years. Serum concentrations of estradiol, testosterone and SHBG were determined by ELISA, glucose and insulin by enzymatic photometry, insulin-like growth factor 1 (IGF-1) by time-resolved fluoroimmunoassays, whole-body fat mass by dual-energy X-ray absorptiometry and HOMA-IR were determined by homeostatic model assessment. The associations were examined using cross-lagged path models.

RESULTS

In a cross-lagged path model, SHBG predicted HOMA-IR before menarche β = -0.320 (95% CI: -0.552 to -0.089), P = 0.007, independent of adiposity and IGF-1. After menarche, no directional effect was found between SHBG and insulin resistance or adiposity.

CONCLUSIONS

Our results suggest that in early puberty, decline in SHBG predicts development of insulin resistance, independent of adiposity. However, after menarche, no directional influences between SHBG, adiposity and insulin resistance were found, suggesting that observational associations between SHBG, adiposity and insulin resistance in pubertal children may be subject to confounding. Further research is needed to understand the underlying mechanisms of the associations between SHBG and cardiometabolic risk markers in peripubertal children.

Sex Hormone-Binding Globulin in Children and Adolescents

Sex hormone-binding globulin (SHBG) is a circulating glycoprotein that transports testosterone and other steroids in the blood. Interest in SHBG has escalated in recent years because of its inverse association with obesity and insulin resistance, and because many studies have linked lower circulating levels of SHBG to metabolic syndrome, type 2 diabetes, nonalcoholic fatty liver disease, polycystic ovary syndrome, and early puberty. The purpose of this review is to summarize molecular, clinical, endocrine, and epidemiological findings to illustrate how measurement of plasma SHBG may be useful in clinical medicine in children.

Growth hormone and reproduction: a review of endocrine and autocrine/paracrine interactions

The somatotropic axis, consisting of growth hormone (GH), hepatic insulin-like growth factor I (IGF-I), and assorted releasing factors, regulates growth and body composition. Axiomatically, since optimal body composition enhances reproductive function, general somatic actions of GH modulate reproductive function. A growing body of evidence supports the hypothesis that GH also modulates reproduction directly, exerting both gonadotropin-dependent and gonadotropin-independent actions in both males and females. Moreover, recent studies indicate GH produced within reproductive tissues differs from pituitary GH in terms of secretion and action. Accordingly, GH is increasingly used as a fertility adjunct in males and females, both humans and nonhumans. This review reconsiders reproductive actions of GH in vertebrates in respect to these new conceptual developments.

Growth hormone (GH) treatment reduces peripheral thyroid hormone action in girls with Turner syndrome

OBJECTIVE

Turner syndrome (TS) is an indication for GH therapy in spite of the modest growth response. Somatic growth depends not only on GH insulin-like growth factor I (IGF-I) axis but also on thyroid hormone (TH) status. We have previously reported that supraphysiological IGF-I levels diminished TH actions in rat tissues by reducing the nuclear TH receptor (TR). GH treatment to TS patients induces high IGF-I levels and therefore a reduction of TH action in tissues may be expected. We aimed at evaluating the effect of GH therapy in TS girls on peripheral TH action.

DESIGN AND PATIENTS

We set up a reverse transcription-polymerase chain reaction (RT-PCR) for TR mRNA estimation in peripheral blood mononuclear cells (PBMC) and compared TR mRNA levels from 10 normal, 10 TS and 10 TS girls under GH therapy (0.33 mg/kg/week for 0.5-2 years).

MEASUREMENTS

After RNA extraction from PBMC, TR and beta-actin mRNAs were coamplified by RT-PCR. In addition serum biochemical markers of TH action were measured: thyrotropin (TSH), sex hormone binding globulin (SHBG), osteocalcin (OC), beta-crosslaps (beta-CL), iodothyronines by electrochemiluminescency and IGF-I by immunoradiometric assay (IRMA) with extraction.

RESULTS

TR mRNAs from PBMC were reduced in TS patients under GH treatment. In turn, serum TSH, OC, beta-CL and IGF-I were increased while SHBG was reduced by GH treatment in TS patients.

CONCLUSIONS

GH treatment reduced TR expression in PBMC and biochemical serum markers of TH action. These results suggest that GH treatment in TS patients impair peripheral TH action at tissue level and prompt a role in the reduced growth response to the therapy.

Effect of recombinant hGH (rhGH) replacement on gonadal function in male patients with organic adult-onset GH deficiency

OBJECTIVE

Previous evidence indicated that, in adults with organic hypopituitarism, GH deficiency (GHD) may mask the presence of other pituitary deficits, in particular central hypothyroidism and hypoadrenalism. Little and conflicting information is available about the relationship between GHD, rhGH therapy and gonadal function in males. The aim of the present study was to investigate the hypothalamic-pituitary-gonadal axis (HPG) in male adults with organic GHD and normal HPG axis.

PATIENTS

Twelve male adults (mean age 48 +/- 7 years) with organic GHD and normal HPG axis.

MEASUREMENTS

Serum levels of testosterone, LH and FSH (basal and after GnRH stimulation test), SHBG and IGF-I and percentage body fat (BF%) were evaluated before and during rhGH (mean dose 0.24 +/- 0.02 mg/day for 13 +/- 1 months) treatment.

RESULTS

Serum IGF-I levels normalized during rhGH treatment and BF% significantly decreased. Serum testosterone levels significantly decreased (from 18.1 +/- 1.7 to 14.2 +/- 1.6 nmol/l, P = 0.01), with a parallel and significant decrease of serum SHBG (from 31.1 +/- 3.6 to 24.3 +/- 2.3 nmol/l, P < 0.05). Thus, calculated free testosterone (cFT) did not change (from 0.39 +/- 0.17 to 0.33 +/- 0.14 nmol/l, P = ns). Finally, no difference was found in basal and GnRH stimulated gonadotrophins levels.

CONCLUSIONS

In conclusion, the condition of GHD does not seem to mask central hypogonadism, in contrast to what is observed for central hypothyroidism and hypoadrenalism. However, the significant decrease in serum testosterone levels, strictly related to SHBG decrease, suggests that evaluation of the HPG axis during rhGH treatment cannot be based on the measurement of total testosterone levels, but should mainly rely on calculation of cFT and a careful clinical evaluation, in order to avoid unnecessary replacement therapy.

Hypothalamic-pituitary-testicular function in prepubertal children with chronic liver disease

Adult patients with chronic liver disease (CLD) show clinical and biochemical signs of hypogonadism and estrogenization. However, no information is available on hypothalamo-pituitary-testicular function in prepubertal or early pubertal children with CLD. Eighteen prepubertal children with CLD, aged 5.8+/-5.5 years (mean +/- SD; range 0.32-12.8), were studied. Most of them had moderate liver function abnormality. Height was slightly decreased (SDS: -1.44-/+1.88) but weight for height was adequate. Serum gonadotropins were evaluated as a function of age. In the age group younger than 1 year (n = 7), serum LH was elevated (4.88+/-6.22 IU/l) when compared with a group of 39 control children (1.2+/-1.65), while serum FSH was normal. In this young group, serum testosterone was normal, but serum estradiol was significantly increased (24.1+/-19.7 pg/ml) when compared with the control group (6.5+/-3.54). In contrast, in the age group older than 2 years, no difference between patients with CLD and controls was observed, either in serum gonadotropins or in serum sex hormones. Taking the 18 patients with CLD together, serum SHBG (113.7+/-51 nmol/l; mean +/- SD) was significantly higher than in normal controls (76+/-38 nmol/l, n = 91, p <0.001). Moreover, and different from normal controls, no change with age was observed in serum SHBG, total testosterone or bioavailable testosterone (non-SHBG-bound). Normal testosterone response to hCG stimulation (>1 ng/ml) was found in a subgroup of 11 children with CLD. By contrast, eight of 11 patients with CLD had an inadequate decrease in SHBG after androgen stimulation. In conclusion, we observed that during the first year of life, a period which includes the postnatal activation of the hypothalamo-pituitary-testicular axis, there is an elevation of serum LH and serum estradiol that suggests the existence of a moderate deficiency of Leydig cell function. This disorder is no longer observed in older prepubertal children. Similar to reports in adults, children with CLD have elevation of serum SHBG levels. Furthermore, the lack of SHBG decrease and bioavailable testosterone increase with age, probably modulated by GH, suggests some degree of hepatic GH resistance in prepubertal patients with CLD.

Determinants of sex hormone-binding globulin in normal postmenopausal women

OBJECTIVE

To examine the factors influencing the levels of sex hormone-binding globulin (SHBG) in normal postmenopausal women by assessing the relationship between SHBG and measured anthropometric, metabolic and hormonal variables.

DESIGN

Cross-sectional, observational study.

SUBJECTS AND METHODS

Seventy normal postmenopausal women aged 47-71 years (mean 58 years), participated in the study. Information was collected on medical, reproductive and smoking history, alcohol use, dietary intake and physical activity. Body composition measurements using dual-energy absorptiometry, and analyses of biochemical and hormonal indices were performed.

RESULTS

Bivariate correlation coefficients indicated that SHBG was inversely related to body weight (r = - 0.44), fat mass (r = - 0.35), and abdominal obesity (r = - 0.42). It was also inversely related to the glucose and insulin levels during an oral glucose tolerance test (- 0.24 < r < - 0.40), serum oestradiol (r = - 0.26), and physical activity (r = - 0.24). Multiple regression analysis indicated that significant independent correlates of SHBG concentration were fat mass, physical activity, alcohol intake, serum oestradiol, and insulin-like growth factor-1, all having a negative impact on SHBG.

CONCLUSIONS

From these observed associations, it is concluded that maintenance of body weight, moderate alcohol consumption, and physical activity will tend to reduce SHBG concentrations in postmenopausal women, thereby increasing the levels of free oestradiol. This mechanism could mediate the beneficial effects of these factors in preventing the development of osteoporosis and cardiovascular disease.

Age-related changes of serum sex hormones, insulin-like growth factor-1 and sex-hormone binding globulin levels in men: cross-sectional data from a healthy male cohort

The age-dependent decline of the gonadal and somatotopic axis has been causally linked to frailty in the elderly by their effects on muscle mass and bone mineral density. However, for healthy men data on serum oestrogens and androgens, as well as IGF-1, as a common outcome measure covering the whole adult age range are scarce. We therefore studied healthy, nonobese male subjects between 20 and 80 years of age to asses their morning concentrations of total (T), free (FT), bioavailable testosterone (bT), oestradiol (E2), bioavailable oestradiol (bE2), oestrone (E1), sex-hormone binding globulin (SHBG), and insulin-like growth factor 1 (IGF-1). Five hundred and seventy-two male healthy volunteers with a BMI < 30 kg/m2 recruited from regular blood donors and senior sports clubs participated in the study. Serum samples were obtained during morning hours and T, FT, E2, E1, SHBG, albumin and IGF-1 were measured by radio-immunoassay systems. In addition, bT and bE2 were calculated. A potential relationship between sex hormones and IGF-1 was tested by multiple regression analysis including age and BMI. Ageing was negatively related to serum levels of sex steroids and IGF-1 (both P < 0.0001) with a mean decrease (youngest vs. oldest) of 51% for T, 64% for FT, 78% for bT, 32% for E2, 62% for bE2, 29% for E1 and 51% for IGF-1 starting in early adulthood whereas SHBG increased after the 5th decade of life (ANOVA P < 0.001). The decline of sex hormones and IGF-1 remained relatively unchanged after adjustment for BMI. Multiple regression analysis revealed an age-and BMI- independent association between oestradiol and IGF-1. In contrast to the female situation sex hormones in healthy, nonobese men decline continuously with age. This process has already started in the third decade, and is paralleled by a decline of IGF-1 serum levels leading to a substantial proportion of elderly men with markedly lowered serum levels of bioavailable sex hormones and IGF-1 compared to the young adult male range. With the recent demonstration of beneficial effects of androgen replacement therapy in healthy males on general well being, muscle mass and bone mineral density the present data may underline the importance of more detailed studies on the biological significance of hormonal changes in men with age.

Hormonal and biochemical parameters and osteoporotic fractures in elderly men

Low testosterone has been associated with hip fracture in men in some studies. However, data on other hormonal parameters and fracture outcome in men is minimal. This study examined the association between free testosterone (free T) estradiol (E2), sex hormone-binding globulin (SHBG), 25-hydroxyvitamin D [25(OH)D], parathyroid hormone (PTH), insulin-like growth factor I (IGF-I), and fracture in 437 elderly community-dwelling men. Age, height, weight, quadriceps strength, femoral neck bone mineral density (FN BMD), and fracture data (1989-1997) also were obtained. Fractures were classified as major (hip, pelvis, proximal tibia, multiple rib, vertebral, and proximal humerus) or minor (remaining distal upper and lower limb fractures). Fifty-four subjects had a fracture (24 major and 30 minor). There was no association between minor fractures and any hormonal parameter. Risk of major fracture was increased 2-fold for each SD increase in age, decrease in weight and height, and increase in SHBG, and risk of major fracture was increased 3-fold for each SD decrease in quadriceps strength, FN BMD, and 25(OH)D (univariate logistic regression). Independent predictors of major fracture were FN BMD, 2.7 (1.5-4.7; odds ratio [OR]) and 95% confidence interval [CI]); 25(OH)D, 2.8 (1.5-5.3); and SHBG, 1.7 (1.2-2.4). An abnormal value for three factors resulted in a 30-fold increase in risk but only affected 2% of the population. It is not immediately apparent how 25(OH)D and SHBG, largely independently of BMD, may contribute to fracture risk. They may be markers for biological age or health status not measured by methods that are more traditional and as such may be useful in identifying those at high risk of fracture.

Collagen metabolism markers as a reflection of bone and soft tissue turnover during the menstrual cycle and oral contraceptive use

Two different groups of women, 23 healthy young adults and 13 women with chronic posterior pelvic pain, were studied before and during use of oral contraceptives (OC). Collagen metabolism markers-here, the amino-terminal propeptide of type I procollagen, the carboxy-terminal telopeptide of type I collagen, and the amino-terminal of procollagen type III-as well as hormones and other endocrine factors indicating the balance between androgen expression/anabolism and catabolism of the subjects (testosterone, sex-hormone binding globulin, and insulin-like growth factor I were measured. Type I procollagen, the carboxy-terminal telopeptide of type I collagen, and the amino-terminal of procollagen type III were all significantly decreased during OC use. These findings implicate OC use-induced changes in collagen type I and III turnover. A shift in the anabolic/catabolic balance was also recorded indicating a less anabolic situation during OC use.

Hormonal and biochemical parameters in the determination of osteoporosis in elderly men

The extent to which changes in several hormonal and biochemical parameters are involved in the pathogenesis of osteoporosis in men remains controversial. This study examined the roles of free testosterone (T), estradiol (E2), sex hormone-binding globulin (SHBG), 25-hydroxyvitamin D, PTH, and insulin-like growth factor I in the determination of bone mineral density (BMD) in 437 community-dwelling elderly men. Age, height, weight, quadriceps strength, and femoral neck (FN) and lumbar spine (LS) BMD were also obtained. In multiple regression analysis, after adjusting for age and weight, low E2 (P = 0.01), and high SHBG (P = 0.0002) levels were common determinants of FN and LS BMD. In addition, high PTH (P = 0.03) was an independent predictor of FN BMD, and low free T (P = 0.02) was an independent predictor of LS BMD. Low free T was associated with FN BMD in univariate analysis only. The hormonal measurements collectively accounted for 5% and 7% of the age- and weight-adjusted variance of FN and LS BMD, respectively. The sex steroids, SHBG and insulin-like growth-I were found to be interrelated using a technique of path analysis that examines the intercorrelation between these variables. A subject with any one abnormal serum parameter had a 4-fold increase in the risk of osteoporosis, whereas three abnormal parameters were associated with an 11-fold increased risk, although the latter group only applied to 1% of the study population. Although the precise causal effects these biochemical parameters may have on the development of osteoporosis remains to be determined, the present findings support an important interrelated role for these hormonal and biochemical parameters on changes in bone density in elderly men.

Comparative effects of GH, IGF-I and insulin on serum sex hormone binding globulin

OBJECTIVE

The serum level of sex hormone binding globulin (SHBG) changes inversely with that of both insulin and insulin-like growth factor (IGF-I), during several nutritional conditions, as well as in response to GH treatment. However, with exogenous IGF-I administration, endogenous IGF-I increases, while insulin decreases. In order to study the separate roles of these hormones in controlling SHBG metabolism, we compared SHBG levels in patients treated with IGF-I and GH.

DESIGN AND PATIENTS

Serum levels of IGF-I, insulin and SHBG were measured before and during the treatment of patients with IGF-I or GH. Blood samples were drawn in the fasting state, prior to and during therapy, 24 hours after drug administration. Sixteen children and adults with Laron syndrome (LS) received daily s.c. injections of IGF-I (120-150 micrograms/kg) for up to 5 months. Three adults with isolated GH deficiency (IGHD) received daily s.c. injections of GH (0.03-0.06 U/kg) for 16 months. Two groups of nine prepubertal children with constitutional short stature (CSS) received GH (0.1 U/kg/day) for 3 months.

MEASUREMENTS

Serum levels of insulin and acid extractable IGF-I were determined by RIA, and that of SHBG by IRMA.

RESULTS

Basal insulin and SHBG levels were within normal range in the LS, IGHD and CSS patients. IGF-I levels were low in LS and IGHD patients, and normal in the CSS children. The mean peak response to chronic therapy was as follows: in LS patients, IGF-I administration decreased insulin levels to 62%, and increased SHBG levels by 64% above basal values. Chronic GH therapy in IGHD caused a marked rise in both IGF-I levels (473%), and insulin levels (96%), and a gradual decline of SHBG to 75% of the basal concentration. In GH treated CSS patients, serum IGF-I peaked at 80% and insulin levels at 102% above the respective basal levels, while SHBG decreased to 83% after 5 days of treatment.

CONCLUSION

The results obtained in Laron syndrome, isolated GH deficiency and constitutional short stature patients treated with IGF-I or GH, indicate that serum insulin had consistently an inverse relation with the levels of circulating SHBG. No relation was found between IGF-I and SHBG levels.

Low circulating levels of insulin-like growth factors and testosterone in chronically institutionalized elderly men

OBJECTIVE

To determine the prevalences of and the associations between hyposomatomedinemia and hypogonadism in healthy young men, healthy old men, and chronically institutionalized old men.

DESIGN

Survey with serial blood tests.

SETTING

Veterans Affairs nursing home and young and old men living in the community.

SUBJECTS

Three groups were studied: healthy young men (20-29 years old, n = 32), healthy old men (59-98 years old, n = 30), and chronically institutionalized old men (59-95 years old, n = 112).

MEASUREMENTS

Plasma insulin-like growth factor-I (IGF-I), total testosterone (TT), free testosterone (FT), and plasma insulin-like growth factor-II (IGF-II) were measured. In subjects with low testosterone level, serum luteinizing hormone (LH) was also determined. In a subset of chronically institutionalized old men with low IGF-I, the serum growth hormone (GH) level was analyzed during the first 4 hours of sleep.

RESULTS

A low IGF-I level (defined as a value below the lower 2.5 percentile of the comparison group) occurred in 85% of the healthy old men when compared with healthy young men (P < 0.001), in 90% of the chronically institutionalized old men when compared with healthy young men (P < 0.001), and in 26% of the chronically institutionalized old men when compared with healthy old men (P < 0.001). In chronically institutionalized old men with low IGF-I compared with healthy young men, nocturnal peaks of serum GH were < 2 ng/mL in most cases. Low TT (defined as a value below the lower 2.5 percentile of the comparison group) occurred in 86% of the healthy old men when compared with healthy young men (P < 0.001), in 88% of the chronically institutionalized old men when compared with healthy young men (P < 0.001), and in 28% of the chronically institutionalized old men when compared with healthy old men (P < 0.001). The results of FT were similar. In 80% of the institutionalized old men with low TT and FT, the serum LH level was low (< 20 mU/mL). In 53% of the institutionalized old men, the IGF-II level was below the lower 2.5 percentile of the healthy old men (P < 0.001). In both healthy and institutionalized old men, IGF-I and IGF-II levels were significantly correlated to each other (r = 0.6), but neither was significantly correlated to TT or FT. In the institutionalized old men, IGF-I was inversely correlated with age and with a diagnosis of dementia; TT and FT were inversely correlated with age and with the degree of dependency in ADL's.

CONCLUSIONS

Compared with healthy young men, most healthy old men have low serum IGF-I, TT, and FT levels. The geriatric hyposomatomedinemia and hypogonadism are more severe in institutionalized old men. In the latter group, both endocrine deficiencies are usually of central origin, but their occurrences are not significantly associated. Healthy old men usually have a low level of IGF-I compared with healthy young men, but a similar level of IGF-II; institutionalized old men are usually low in both values.

Hormonal and clinic evaluation of patients with moderate body hair growth

Plasma prolactin (PRL), gonadotropins (FSH, LH), estradiol-17 beta (E2), progesterone (P), total testosterone (T), sex steroid binding protein (SBP), T/SBP index, cortisol (F), 17-OH-progesterone (17OH-P), dehydroepiandrosterone sulphate (DHEA-S) and androstenedione (A), were measured in 50 fertile non-obese women presenting with moderate body hair growth and in 30 matched controls. DHEA-S and PRL were significantly higher (P < 0.002, P < 0.001, respectively) and SBP was lower (P < 0.001) in patients than in controls. Regression analyses showed that PRL levels were independent of the other parameters, while a negative correlation was found between DHEA-S and SBP values. Since the decision to treat a woman with mild body hair growth is usually a clinical one, PRL behaviour has to be taken into account before deciding the type of treatment. Clinical improvement was observed in subjects treated with ethynylestradiol plus desogestrel or plus cyproterone acetate, so as to produce an increase in SBP rather than a decrease in DHEA-S.

Effect of growth hormone administration on human ovarian function and steroidogenic gene expression in granulosa-luteal cells

OBJECTIVE

To study the effect of growth hormone (GH) in combination with an ultrashort-term gonadotropin-releasing hormone analogue/human menopausal gonadotropin (hMG)/human chorionic gonadotropin (hCG) regimen in ovarian hyperstimulation for in vitro fertilization (IVF).

DESIGN

Prospective randomized placebo-controlled study.

SETTING

University-based IVF program.

PATIENTS

Fifty-four normally cycling women (27 control and 27 GH-treated) participated in this study.

INTERVENTIONS

Human recombinant GH (24 IU)/placebo was given intramuscularly on alternate days starting on cycle day 4 until the day of last hMG injection.

RESULTS

Serum estradiol (E2) and progesterone (P) concentrations were slightly lower in the GH group than in the placebo group on the day of hCG injection and 1 day thereafter (P < 0.01 to 0.001). Serum luteinizing hormone, follicle-stimulating hormone, prolactin, testosterone (T), and sex hormone-binding globulin did not differ between the groups. The follicular fluid (FF) concentration of T was higher in the GH group than in the placebo group (15.9 +/- 6.0 nmol/L versus 10.2 +/- 4.9 nmol/L, P < 0.005), and no differences were observed in the FF concentrations of E2, P, and insulin-like growth factor I between the groups. In granulosa cells isolated from patients who received GH treatment, the levels of 3 beta-hydroxysteroid dehydrogenase and aromatase messenger ribonucleic acid were significantly higher than in the patients receiving placebo. The number of hMG ampules needed for follicular development and the number of follicles and oocytes recovered were similar in both groups.

CONCLUSIONS

These results indicate that GH administration modifies ovarian steroidogenic response to gonadotropins in IVF patients, suggesting a role for GH in the regulation of human ovarian function.

Steroidal and non-steroidal factors in plasma sex hormone binding globulin regulation

Sex hormone binding globulin (SHBG) is a specific steroid-binding plasma glycoprotein regulated by several factors. Sex steroids are currently considered to be the main physiological regulators of this protein. SHBG levels, in fact, increase during estrogen treatment and decrease after androgen administration. It is well known, however, that in many physiological and pathological conditions SHBG concentrations cannot be explained only on the basis of steroidal control mechanisms. The regulation of SHBG levels is in fact more complex and other factors can also affect its plasma values. Between the steroidal factors our attention was focused on the role of androgens, of glandular and peripheral origin, in their capacity to lower SHBG plasma levels. We studied hyperandrogenic conditions in prepubertal (65 subjects with precocious adrenarche and 16 girls with prepubertal hypertrichosis, aged between 4 and 8 years) and in adult age (51 hirsute patients aged between 14-35 years and 51 acneic patients aged between 15-40 years). The effects of dexamethasone and ACTH administration on SHBG plasma levels were also evaluated. The results obtained showed that in adult hyperandrogenic patients SHBG levels, significantly lower than in controls, were not always inversely correlated with androgen levels, which, on the contrary, were higher than in controls. In patients with precocious adrenarche we found an inverse correlation only between SHBG, which was significantly lower than normal, and body mass index or bone age but not with androgens, suggesting that in this condition other factors may be more relevant than steroids in SHBG regulation. Between the non-steroidal factors our attention focused on insulin. We studied 40 non-obese hyperandrogenic patients with or without ultrasonographic evidence of polycystic ovaries, aged 18-39 years, and 35 obese patients, aged 19-37 years, with or without hyperandrogenism or evidence of PCO. Low levels of SHBG were found not only in hyperandrogenic obese patients but also in obese patients with normal androgens. It is possible to conclude that (1) several factors (calorie intake, energy balance and growth factors), other than steroids, may be involved in the regulation of SHBG levels in plasma; and (2) each regulating factor may act to a different extent depending on the various periods of the life cycle.

High serum sex hormone-binding globulin (SHBG) in premature thelarche

OBJECTIVE

We determined serum sex hormone-binding globulin (SHBG), serum dehydroepiandrosterone sulphate, serum oestradiol and serum testosterone and its fractions in girls with premature thelarche.

DESIGN

Blood was drawn from girls with recently diagnosed (3-12 weeks) premature thelarche. Serum was kept frozen for at least one year before hormonal determination to exclude precocious puberty by clinical evaluation.

PATIENTS

Seventeen girls with premature thelarche aged 0.83-7.16 years were studied, and compared with a group of 22 normal prepubertal girls.

MEASUREMENTS

SHBG was measured by saturation analysis and serum dehydroepiandrosterone sulphate, serum total oestradiol and serum total testosterone were determined by radioimmunoassay. Non-SHBG-bound testosterone and free testosterone were calculated from an equation derived from the law of mass action.

RESULTS

Median serum SHBG in premature thelarche was 137 nmol/l (range 64-221), significantly higher than in normal controls, 93.7 (32-172) (P < 0.05) non-parametric test of medians. Serum SHBG decreased significantly with age in controls but not in premature thelarche. No difference was found in serum dehydroepiandrosterone sulphate. Median serum total testosterone (0.34 nmol/l, 0.17-0.97), median serum non-SHBG-bound testosterone (0.04 nmol/l, 0.02-0.10) and median free testosterone (2.2 pmol/l, 1.0-4.5) were significantly lower in premature thelarche than in control (P < 0.001).

CONCLUSIONS

Serum SHBG is high and bioavailable T is low in girls with premature thelarche. This might alter the oestrogen/androgen ratio in the breast.

Regulation of sex hormone-binding globulin production by growth factors

Sex hormone-binding globulin (SHBG) is a glycoprotein whose production has been demonstrated to be regulated by both sex steroids, as well as by thyroid hormone and peptide hormones such as insulin. However, none of these regulatory factors would explain the marked decrease in serum SHBG seen throughout the prepubertal and pubertal time period in both boys and girls. Furthermore, current in vitro data show that both androgens and estrogens can stimulate SHBG production by the human hepatoblastoma cell line Hep G2; yet, in vivo androgens appear to suppress SHBG levels, while estrogens are associated with elevated levels. This study was undertaken to determine possible mechanisms to explain this phenomenon. Hep G2 cell cultures were incubated with insulin-like growth factor I (IGF-I), epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), or dehydroepiandrosterone (DHEA). Significant decreases in the level of SHBG in the culture medium relative to control cultures occurred for each of the growth factors (P less than .01), whereas an increase in SHBG levels was observed in the medium of DHEA-treated cells. When cells were coincubated with IGF-I and thyroxine (T4), which alone stimulates SHBG production both in vivo and in vitro, the SHBG response to T4 was blunted. These results suggest that growth factors, as well as insulin, may be important determinants in SHBG production.

On the regulation of sex-hormone-binding globulin--a challenge of an old dogma and outlines of an alternative mechanism

In this review, the different factors known to affect SHBG levels are discussed with respect to their possible significance in the physiological regulation of this protein: Sex steroids, puberty, nutritional status, thyroid hormones and liver disease. It is concluded that the serum levels of SHBG are related to general metabolic factors, nutritional status, growth and ageing than to the estrogen/androgen balance. The authors suggest that SHBG is regulated primarily by growth hormone, somatomedin-C and possibly other growth factors. Growth hormone may promote SHBG synthesis in the liver while somatomedin-C may stimulate its extravasation and uptake in target tissues. It is suggested that sex steroids merely have an indirect, modulating influence.