Serum levels of insulin-like growth factor I and insulin-like growth factor-binding protein 1 correlate with serum free testosterone and sex hormone binding globulin levels in healthy young and middle-aged men

Hypogonadism is frequent in very old men with multimorbidity and is associated with anemia and sarcopenia

BACKGROUND

Clinical data regarding hypogonadism in very old men with multimorbidity are rare. Hypogonadism can contribute to osteoporosis, anemia and sarcopenia and is therefore a relevant problem for geriatric patients.

METHODS

A total of 167 men aged 65-96 years (mean 81 ± 7 years) admitted to an acute geriatric ward were included in a cross-sectional study. Body composition derived from dual-energy X‑ray absorptiometry, bone mineral density, handgrip strength, multimorbidity, polypharmacy and laboratory values were obtained from the routine electronic clinical patient file.

RESULTS

Hypogonadism was present in 62% (n = 104) of the study participants, of whom 83% showed clinical manifestation of hypogonadism (hypogonadism in combination with anemia, sarcopenia and/or low T‑score). The subgroups showed a distribution of 52% primary and 48% secondary hypogonadism. Compared to the eugonadal patients, hypogonadal patients had reduced handgrip strength (p = 0.031) and lower hemoglobin levels (p = 0.043), even after adjustment for age, body mass index and glomerular filtration rate.

CONCLUSION

Hypogonadism is common in geriatric patients. If chronic anemia, sarcopenia, or osteoporosis are diagnosed, testosterone levels should be determined in geriatric settings.

Semen quality in hypogonadal acromegalic patients

OBJECTIVE

Growth hormone (GH) activity might be implicated in male reproductive function. One previous study has suggested significantly reduced semen quality in untreated acromegalic patients due to both reduced sperm counts and sperm motility.

DESIGN AND METHODS

A retrospective study comprising ten uncontrolled hypogonadal acromegalic patients (median age 29 years) who delivered semen for cryopreservation before initiation of testosterone therapy. Semen variables and hormone concentrations were compared to those of ten non-acromegalic hypogonadal men with pituitary disease (age 31 years) and those of young healthy men.

RESULTS

Acromegalic patients vs. non-acromegalic patients had a higher percentage of progressive motile spermatozoa (62 vs. 47%, p = 0.04). Eight of ten acromegalic patients and 82% of controls had total sperm counts above 39 million and progressive motile spermatozoa above 32% (p = 0.55), corresponding to the WHO 2010 reference levels for expected normal fertility for these variables. Non-acromegalic patients vs. healthy controls had reduced percentage of progressive motile spermatozoa (47 vs. 57%, p = 0.02) and only five of ten patients had semen quality above the WHO reference level, which was significantly lower than observed in healthy controls (p = 0.022). Total sperm counts were similar between both patient groups and controls. There were no differences in reproductive hormone levels between acromegalic patients vs. non-acromegalic patients (p-values between 0.10 and 0.61). Compared to healthy controls both patient groups had severely reduced serum testosterone, calculated free testosterone.

CONCLUSIONS

Despite severe hypoandrogenism acromegalic patients had semen quality similar to healthy controls based on determination of the number of progressively motile spermatozoa. By contrast non-acromegalic pituitary patients had reduced sperm motility. Our data do not support reduced semen quality in acromegaly.

Association between GH receptor polymorphism (exon 3 deletion), serum IGF1, semen quality, and reproductive hormone levels in 838 healthy young men

INTRODUCTION

GH activity may be involved in male reproductive function. A common genetic polymorphism in the gene encoding the GH receptor (GHR) results in deletion of the entire exon 3 sequence (GHRd3 isoform). The short GHRd3/d3 isoform seems more sensitive compared with full-length receptors (GHRfl/fl).

AIM

TO INVESTIGATE THE ASSOCIATIONS BETWEEN GH ACTIVITY, EVALUATED BY EXON 3 GHR POLYMORPHISM, AND SERUM IGF1 VS REPRODUCTIVE HORMONES, SEMEN QUALITY, AND PRE- AND POSTNATAL GROWTH IN HEALTHY YOUNG MALES (N=838, MEAN AGE: 19.4 years).

RESULTS

Compared with GHRfl/fl homozygous individuals (n=467) GHRd3/d3 homozygous individuals (n=69) tended to have larger semen volume (3.2 (2.4-4.3) vs 3.6 (2.6-4.7) ml, P=0.053) and higher serum inhibin-B levels (208 pg/ml (158-257) vs 227 pg/ml (185-264), P=0.050). Semen quality, levels of gonadotropins, testosterone, estradiol, sex hormone-binding globulin, and IGF1 were not associated with GHRd3 genotype. A twofold increase in serum IGF1 was associated with a 13% (4-23) increase in calculated free testosterone (P=0.004). By contrast IGF1 was inversely associated with serum inhibin-B (P=0.027), but showed no associations to semen quality. GHR genotype and serum IGF1 were not associated with size at birth or final height.

CONCLUSIONS

GHRd3 polymorphism seemed only to have a weak influence on male reproductive function of borderline significance. The sensitive GHRd3/d3 genotype may slightly increase testicular function, as evaluated by semen volume and levels of inhibin-B, but does not seem to influence Leydig cell steroidogenesis. GHR genotype did not influence pre- and postnatal growth.

Association between endogenous sex steroid hormones and insulin-like growth factor proteins in US men

PURPOSE

Sex steroid hormone concentrations and insulin-like growth factor (IGF) proteins have been independently associated with risk of cancer, chronic diseases, and mortality. However, studies that evaluated the inter-relation between the sex hormones and IGF pathways have provided mixed results. We examined the association between endogenous sex hormones and sex hormone-binding globulin (SHBG) with IGF-1 and IGF-binding protein 3 (IGFBP-3) in a population-based sample of US men.

METHODS

Data from 1,135 men aged 20 years or older participating in the third National Health and Nutrition Examination Survey (NHANES III) were analyzed. Weighted linear regression was used to estimate geometric means and 95 % confidence intervals for IGF-1 and IGFBP-3 concentrations by sex steroid hormones and SHBG after adjusting for age, race/ethnicity, body mass index, waist circumference, alcohol consumption, cigarette smoking, physical activity, diabetes, and mutually adjusting for other sex hormones and SHBG.

RESULTS

No significant association was observed between sex steroid hormones, SHBG, and IGF-1 concentrations. Total estradiol (% difference in Q5 - Q1 geometric means -9.7 %; P-trend 0.05) and SHBG (% difference -7.3 %; P-trend 0.02) were modestly inversely associated with IGFBP-3. Total testosterone was modestly inversely associated with IGFBP-3 (% difference -6.2 %; P-trend 0.01), but this association disappeared after adjustment for total estradiol and SHBG (% difference 2.6 %; P-trend 0.23). Androstanediol glucuronide was not associated with IGFBP-3.

CONCLUSIONS

These findings suggest that there may be inter-relationships between circulating total estradiol, SHBG, and IGFBP-3 concentrations. Future research may consider these inter-relationships when evaluating potential joint effects of the sex hormones and IGF pathways.

Sex hormones in Malay and Chinese men in Malaysia: are there age and race differences?

OBJECTIVES

Variations in the prevalence of sex-hormone-related diseases have been observed between Asian ethnic groups living in the same country; however, available data concerning their sex hormone levels are limited. The present study aimed to determine the influence of ethnicity and age on the sex hormone levels of Malay and Chinese men in Malaysia.

METHODS

A total of 547 males of Malay and Chinese ethnicity residing in the Klang Valley Malaysia underwent a detailed screening, and their blood was collected for sex hormones analyses.

RESULTS

Testosterone levels were normally distributed in the men (total, free and non-sex hormone-binding globulin (SHBG) bound fractions), and significant ethnic differences were observed (p<0.05); however, the effect size was small. In general, testosterone levels in males began to decline significantly after age 50. Significant ethnic differences in total, free and non-SHBG bound fraction estradiol levels were observed in the 20-29 and 50-59 age groups (p<0.05). The estradiol levels of Malay men decreased as they aged, but they increased for Chinese men starting at age 40.

CONCLUSIONS

Small but significant differences in testosterone levels existed between Malay and Chinese males. Significant age and race differences existed in estradiol levels. These differences might contribute to the ethnic group differences in diseases related to sex hormones, which other studies have found in Malaysia.

Sex steroids and bone health status in men

Male osteoporosis is a health problem which deserves more attention as nearly 30% of osteoporotic fractures happen in men aged 50 years and above. Although men do not experience an accelerated bone loss phase and testosterone deficiency is not a universal characteristic for aged men, osteoporosis due to age-related testosterone deficiency does have a negative impact on bone health status of men. Observations from epidemiological studies indicate that elderly men with higher testosterone can preserve their BMD better and thus are less prone to fracture. Observations on men with estrogen resistance or aromatase deficiency indicate that estrogen is equally important in the maintenance of bone health status. This had been validated in several epidemiological studies which found that the relationships between estrogen and bone health indices are significant and sometimes stronger than testosterone. Studies on the relationship between quantitative ultrasound and bone remodeling markers suggest that testosterone and estrogen may have differential effects on bone, but further evidence was needed. In conclusion, both testosterone and estrogen are important in the maintenance of bone health in men.

Hormone replacement therapy and physical function in healthy older men. Time to talk hormones?

Improving physical function and mobility in a continuously expanding elderly population emerges as a high priority of medicine today. Muscle mass, strength/power, and maximal exercise capacity are major determinants of physical function, and all decline with aging. This contributes to the incidence of frailty and disability observed in older men. Furthermore, it facilitates the accumulation of body fat and development of insulin resistance. Muscle adaptation to exercise is strongly influenced by anabolic endocrine hormones and local load-sensitive autocrine/paracrine growth factors. GH, IGF-I, and testosterone (T) are directly involved in muscle adaptation to exercise because they promote muscle protein synthesis, whereas T and locally expressed IGF-I have been reported to activate muscle stem cells. Although exercise programs improve physical function, in the long-term most older men fail to comply. The GH/IGF-I axis and T levels decline markedly with aging, whereas accumulating evidence supports their indispensable role in maintaining physical function integrity. Several studies have reported that the administration of T improves lean body mass and maximal voluntary strength in healthy older men. On the other hand, most studies have shown that administration of GH alone failed to improve muscle strength despite amelioration of the detrimental somatic changes of aging. Both GH and T are anabolic agents that promote muscle protein synthesis and hypertrophy but work through separate mechanisms, and the combined administration of GH and T, albeit in only a few studies, has resulted in greater efficacy than either hormone alone. Although it is clear that this combined approach is effective, this review concludes that further studies are needed to assess the long-term efficacy and safety of combined hormone replacement therapy in older men before the medical rationale of prescribing hormone replacement therapy for combating the sarcopenia of aging can be established.

Common genetic variation within IGFI, IGFII, IGFBP-1, and IGFBP-3 and endometrial cancer risk

OBJECTIVE

The insulin-like growth factor (IGF) pathway plays a critical role in the growth and development of the uterus and is believed to function as a mediator of steroid hormone actions in the endometrium. The local expression of genes encoding IGFs and IGF-binding proteins (IGFBPs) is important in determining IGF bioactivity in the uterus. Genetic variation in key genes within the IGF pathway may influence the rate of cellular proliferation and differentiation in the uterus and ultimately affect the risk of endometrial cancer. Our hypothesis is that variant alleles in key genes involved in the IGF pathway will influence the development of endometrial cancer.

METHODS

We conducted a case-control study nested within the Nurses' Health Study (NHS) and the Women's Health Study (WHS) to investigate the association between forty-four polymorphisms within IGFI, IGFII, IGFBP-1, and IGFBP-3 with endometrial cancer risk using 692 invasive endometrial cancer cases and 1723 matched controls. We used conditional logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs) to assess the risk of endometrial cancer.

RESULTS

We observed an inverse association with IGFII rs3741211 and endometrial cancer risk (OR=0.79 (95% CI: 0.63, 0.99)) and IGFII rs1004446 and endometrial cancer risk (OR=0.80 (95% CI: 0.68, 0.94)). We also observed an inverse association with IGFBP-3 rs2453839 and endometrial cancer risk (OR=0.81 (95%CI: 0.67, 0.98). However, we did not observe any statistically significant associations with the polymorphisms in IGFI and IGFBP1 and endometrial cancer risk.

CONCLUSIONS

Genetic variation with IGFII and IGFBP-3 may influence endometrial cancer risk in Caucasians. Polymorphisms in IGFI and IGFBP-1 were not associated with endometrial cancer risk, but further research is needed.

Regulation of growth hormone action by gonadal steroids

Sex steroids modulate growth hormone (GH) secretion and action. Estrogen attenuates GH action in a dose- and route-dependent manner by inhibiting GH-regulated endocrine function of the liver. Testosterone amplifies the metabolic action of GH while exhibiting similar but independent effects of its own. The strong modulatory effect of gonadal steroids on GH responsiveness provides insights into the biologic basis of sexual dimorphism in growth, development, and body composition and practical information for the clinical endocrinologist in the treatment of hypopituitary patients.

Gender, body weight, disease activity, and previous radiotherapy influence the response to pegvisomant

CONTEXT/OBJECTIVE

To effectively normalize IGF-I in patients with acromegaly, various covariates may affect dosing and plasma concentrations of pegvisomant. We assessed whether sex, age, weight, and previous radiotherapy influence dosing of pegvisomant in patients with active disease.

DESIGN

Data from 69 men and 49 women participating in multicenter, open-label trials of pegvisomant were retrospectively evaluated using multiple regression techniques. Sixty-nine subjects (39 men, 30 women) had undergone external beam pituitary radiotherapy. Serum IGF-I was at least 30% above age-related upper limit of normal in all patients at study entry. After a loading dose of pegvisomant (80 mg), patients were commenced on 10 mg/d. Pegvisomant dose was adjusted by 5 mg every eighth week until serum IGF-I was normalized.

RESULTS

At baseline, men had significantly higher mean serum IGF-I levels than women despite similar GH levels. After treatment with pegvisomant, IGF-I levels were similar in men and women. A significant correlation between baseline GH, IGF-I, body weight, and the dose of pegvisomant required to normalize serum IGF-I was observed (all P < 0.001). Women required an average of 0.04 mg/kg more pegvisomant than men and a mean weight-corrected dose of 19.2 mg/d to normalize serum IGF-I [14.5 mg/d (men); P < 0.001]. Patients treated with radiotherapy required less pegvisomant to normalize serum IGF-I despite similar baseline GH/IGF-I levels (15.2 vs. 18.5 mg/d for no previous radiotherapy; P = 0.002).

CONCLUSIONS

Sex, body weight, previous radiotherapy, and baseline GH/IGF-I influence the dose of pegvisomant required to normalize serum IGF-I in patients with active acromegaly.

Modulation of growth hormone action by sex steroids

Growth hormone (GH) is a major regulator of growth, somatic development and body composition. Sex steroids can act centrally by regulating GH secretion and peripherally modulating GH responsiveness. This review addresses data of potential clinical relevance on how sex steroids modulate GH secretion and action, aiming to increase the understanding of sex steroid/GH interactions and leading to improved management of patients. Sex steroids regulate GH secretion directly as well as indirectly through IGF-I modulation. Testosterone stimulates GH secretion centrally, an effect dependent on prior aromatization to oestrogen. Oestrogen stimulates GH secretion indirectly by reducing IGF-I feedback inhibition. Whether oestrogen stimulates GH secretion centrally in females is unresolved. Gonadal steroids modify the metabolic effects of GH. Testosterone amplifies GH stimulation of IGF-I, sodium retention, substrate metabolism and protein anabolism while exhibiting similar but independent actions of its own. Oestrogen attenuates GH action by inhibiting GH-regulated endocrine function of the liver. This is a concentration-dependent phenomenon that arises invariably from oral administration of therapeutic doses of oestrogen, an effect that can be avoided by using a parenteral route. This strong modulatory effect of gonadal steroids on GH responsiveness provides insights into the biological basis of sexual dimorphism in growth, development and body composition and practical information for the clinical endocrinologist. It calls for an appraisal of the diagnostic criteria for GH deficiency of GH stimulation tests, which currently are based on arbitrary cut-offs that do not take into account the shifting baseline from the changing gonadal steroid milieu. In the management of GH deficiency in the hypopituitary female, oestrogen should be administered by a nonoral route. In hypopituitary men, androgens should be replaced concurrently to maximize the benefits of GH. In the general population, the metabolic consequences of long-term treatment of women with oral oestrogen compounds, including selective oestrogen receptor modulators, are largely unknown and warrant study.

Implications for the role of diet in acne

Within the dermatology community, a general consensus has emerged that diet is unrelated to the etiology of acne. Except for 2 poorly designed studies, now more than 30 years old, there are few objective data to support this notion. In contrast, a large body of evidence now exists showing how diet may directly or indirectly influence the following 5 proximate causes of acne: (1) increased proliferation of basal keratinocytes within the pilosebaceous duct, (2) incomplete separation of ductal corneocytes from one another via impairment of apoptosis and subsequent obstruction of the pilosebaceous duct, (3) androgen-mediated increases in sebum production, (4) colonization of the comedo by Propionibacterium acnes, and (5) inflammation both within and adjacent to the comedo. This article will provide a review of the currently available literature on the association between diet and acne vulgaris as well as a discussion of the physiologic principles that may underlie this association.

The decline of androgen levels in elderly men and its clinical and therapeutic implications

Aging in men is accompanied by a progressive, but individually variable decline of serum testosterone production, more than 20% of healthy men over 60 yr of age presenting with serum levels below the range for young men. Albeit the clinical picture of aging in men is reminiscent of that of hypogonadism in young men and decreased testosterone production appears to play a role in part of these clinical changes in at least some elderly men, the clinical relevancy of the age-related decline in sex steroid levels in men has not been unequivocally established. In fact, minimal androgen requirements for elderly men remain poorly defined and are likely to vary between individuals. Consequently, borderline androgen deficiency cannot be reliably diagnosed in the elderly, and strict differentiation between "substitutive" and "pharmacological" androgen administration is not possible. To date, only a few hundred elderly men have received androgen therapy in the setting of a randomized, controlled study, and many of these men were not androgen deficient. Most consistent effects of treatment have been on body composition, but to date there is no evidence-based documentation of clinical benefits of androgen administration to elderly men with normal or moderately low serum testosterone in terms of diminished morbidity or of improved survival or quality of life. Until the long-term risk-benefit ratio for androgen administration to elderly is established in adequately powered trials of longer duration, androgen administration to elderly men should be reserved for the minority of elderly men who have both clear clinical symptoms of hypogonadism and frankly low serum testosterone levels.

Gender differences in the relation of insulin-like growth factor binding protein-1 to cardiovascular risk factors: a population-based study

OBJECTIVE

A possible involvement of insulin-like growth factor-I (IGF-I) and its binding protein IGFBP-1 in the pathogenesis of cardiovascular disorder has been suggested. However, few publications have addressed the gender differences in cardiovascular risk factors in relation to the IGF/IGFBP system. The aim of the present study was to study gender differences in the relationship between fasting serum levels of IGFBP-1 and cardiovascular risk factors in a normal population of men and women.

DESIGN

Cross-sectional study. Patients A normal population of 273 men and women aged 20-74 years.

MEASUREMENTS

A medical examination was performed and blood drawn in the morning after subjects had been fasting overnight. Before the examination, they were asked to fill out a questionnaire concerning lifestyle and psychosocial factors.

RESULTS

Fasting IGFBP-1 was lower in men than in women and was positively correlated to age in men but not in women. The men had in general a more disadvantageous cardiovascular risk profile than women, with several indicators of the metabolic syndrome: higher blood pressure and higher serum levels of total cholesterol, triglycerides, low density lipoprotein cholesterol (LDL-C), plasma-glucose and insulin, as well as lower IGFBP-1. Women had lower physical activity, lower consumption of alcohol, and lower values on indicators of psychosocial and mental health but had a healthier diet. Our findings indicate that low circulating levels of IGFBP-1 are associated with the well-known risk factors of cardiovascular disease; however, the association showed a different pattern for men and women. In men we found a negative association with body mass index (BMI), insulin resistance and diastolic blood pressure, and a positive association with SHBG, cortisol and testosterone. For women low IGFBP-1 appears in negative associations with BMI, waist-hip ratio (WHR), insulin resistance and testosterone, and in positive associations with SHBG and cortisol. Significant gender differences in the correlation with IGFBP-1 are seen for testosterone, cortisol, SHBG, WHR and oestradiol. For HDL-C and diastolic blood pressure the gender difference in correlation was at the limit of significance (P < 0.10).

CONCLUSION

Low circulating levels of IGFBP-1 are associated with the well-known risk factors of cardiovascular disease; however, the association showed a different pattern for men and women. The most marked gender differences in the correlation with IGFBP-1 are seen for testosterone, cortisol, SHBG, WHR, oestradiol, HDL-C and diastolic blood pressure. Our study emphasizes the importance of separate analyses for men and women. The results presented are a step towards gaining a better understanding of the gender differences in cardiovascular disease and in the regulation of IGFBP-1, though further prospective studies are needed.

Supraphysiological growth hormone: less fat, more extracellular fluid but uncertain effects on muscles in healthy, active young adults

OBJECTIVES

To study the effects on body composition after 1 month's administration of supraphysiological doses of growth hormone (GH) in healthy, active young adults with normal GH-IGF-I axis.

SUBJECTS AND METHODS

Thirty healthy, physically active volunteers (15 men and 15 women), mean age 25.9 years (range 18-35), participated in this study, designed as a randomized, double-blind, placebo-controlled, parallel study with three groups (n = 10: five men and five women in each group). The groups comprised the following: placebo (P), GH 0.1 IU/kg/day [0.033 mg/kg/day] (GH 0.1) and GH 0.2 IU/kg/day [0.067 mg/kg/day] (GH 0.2).

RESULTS

In the pooled group with active GH treatment (n = 20) the results showed significant increases: IGF-I increased by 134% (baseline vs. after 1 month), body weight by 2.7%, fat free mass by 5.3%, total body water by 6.5% and extracellular water (ECW) by 9.6%. Body fat decreased significantly by 6.6%. No significant change in intracellular water was detected. The observed increase in fat free mass by 5.3% was explained by the ECW increase, indicating limited anabolic effects of the supraphysiological GH doses. Changes were noticeable in both genders, although more prominent in the male subjects. Fluid retention symptoms occurred in the majority of individuals.

CONCLUSIONS

This is, to our knowledge, the first placebo-controlled trial to show the effects of supraphysiological GH doses on body composition and IGF-I levels in physically active and healthy individuals of both genders; the results indicate limited anabolic effects of GH with these supraphysiological doses. The role of GH as an effective anabolic doping agent is questioned.

Hyperinsulinemic diseases of civilization: more than just Syndrome X

Compensatory hyperinsulinemia stemming from peripheral insulin resistance is a well-recognized metabolic disturbance that is at the root cause of diseases and maladies of Syndrome X (hypertension, type 2 diabetes, dyslipidemia, coronary artery disease, obesity, abnormal glucose tolerance). Abnormalities of fibrinolysis and hyperuricemia also appear to be members of the cluster of illnesses comprising Syndrome X. Insulin is a well-established growth-promoting hormone, and recent evidence indicates that hyperinsulinemia causes a shift in a number of endocrine pathways that may favor unregulated tissue growth leading to additional illnesses. Specifically, hyperinsulinemia elevates serum concentrations of free insulin-like growth factor-1 (IGF-1) and androgens, while simultaneously reducing insulin-like growth factor-binding protein 3 (IGFBP-3) and sex hormone-binding globulin (SHBG). Since IGFBP-3 is a ligand for the nuclear retinoid X receptor alpha, insulin-mediated reductions in IGFBP-3 may also influence transcription of anti-proliferative genes normally activated by the body's endogenous retinoids. These endocrine shifts alter cellular proliferation and growth in a variety of tissues, the clinical course of which may promote acne, early menarche, certain epithelial cell carcinomas, increased stature, myopia, cutaneous papillomas (skin tags), acanthosis nigricans, polycystic ovary syndrome (PCOS) and male vertex balding. Consequently, these illnesses and conditions may, in part, have hyperinsulinemia at their root cause and therefore should be classified among the diseases of Syndrome X.

Effects of dietary intervention on IGF-I and IGF-binding proteins, and related alterations in sex steroid metabolism: the Diet and Androgens (DIANA) Randomised Trial

OBJECTIVE

To assess the effects of a comprehensive change in dietary composition on endogenous hormone metabolism. The specific aim was to examine whether this intervention could lead to favourable changes in insulin sensitivity, levels of IGF-I and IGF-binding proteins (IGFBPs), and total and bioavailable testosterone and estradiol, that would be expected to reduce breast cancer risk.

DESIGN

Randomised dietary intervention study; duration of 5 months.

SUBJECTS

From a total of 99 postmenopausal women, who had elevated baseline plasma testosterone levels, 49 women were randomly assigned to the dietary intervention arm and the other 50 to a control group.

INTERVENTIONS

Main aspects of the dietary intervention were reductions in the intake of total fat and refined carbohydrates, an increase in the ratio of n-3 over n-6 plus saturated fatty acids, and increased intakes of foods rich in dietary fibre and phytooestrogens.

RESULTS

Relative to the control group, women of the intervention group showed a significant reduction of body weight, waist circumference, fasting serum levels of testosterone, C peptide, glucose, and insulin area after glucose tolerance test, and a significant increase of serum levels of sex hormone-binding globulin, IGFBP-1, -2, and growth hormone-binding protein. Serum levels of IGF-I did not change.

CONCLUSION

This comprehensive dietary intervention strategy proved to be successful in inducing changes in endogenous hormone metabolism that might eventually result in reduced breast cancer risk. Additional studies are needed to show whether the dietary intervention and related hormonal changes can be both maintained over longer periods, of at least several years.

Interrelationships between plasma testosterone, SHBG, IGF-I, insulin and leptin in prostate cancer cases and controls

Despite strong indirect evidence that androgens stimulate prostate cancer development, data from most analytical studies on this association have been negative. To further investigate this issue, we studied the interrelationships between androgenicity and insulin-like growth factor I (IGF-I), insulin and leptin. Within a prospective cohort study, we measured testosterone, sex hormone-binding globulin (SHBG) and IGF-I, IGF-binding protein (IGFBP)-1, IGFBP-3, insulin and leptin, in plasma from 149 cases and 298 controls. Testosterone correlated positively with SHBG, whereas testosterone and SHBG correlated inversely with IGF-I, IGFBP-3, insulin, leptin and body mass index (BMI). Indices of free testosterone showed an inverse linear correlation with leptin (P<0.01), and a strong drop in the 5th quintile of BMI. However, levels of free testosterone showed non-linear relationships over quintiles of insulin and IGF-I, with a significant increase in the second quintile of IGF-I compared with other levels. The absence of an association between plasma levels of androgens and prostate cancer risk in analytical studies, despite the strong indirect evidence of their tumour-stimulating effects, may reflect the complex and mostly inverse associations of androgenicity to IGF-I, insulin and leptin which are hormones that have also been implicated as risk factors for prostate cancer.

Timing of onset of growth hormone deficiency is a major influence on insulin-like growth factor I status in adult life

OBJECTIVE

Several reports have suggested that IGF-I levels in patients with childhood-onset (CO) GH deficiency are lower than those observed in patients with adult-onset (AO) GH deficiency. However, these reports are unsatisfactory as there are several differences between the cohorts studied other than the timing of onset of GH deficiency; in particular, the patients were not matched for equal severity of GH deficiency. We have pursued this question further by examining the IGF-I standard deviation score (SDS) in patients with CO and AO GH deficiency, with equal degrees of severity of GH deficiency, as defined by the peak GH response to the insulin tolerance test (ITT).

PATIENTS AND MEASUREMENTS

IGF-I SDS were compared in 146 non acromegalic patients (69 male), aged 15.7-76.6 years (median 33.4 years), bone mass index (BMI) 27.8 +/- 5.8 kg/m2, with severe GH deficiency (peak GH response < 9 mU/l to insulin-induced hypoglycaemia). Patients were subdivided by timing of onset of GH deficiency and the peak GH response to the ITT (GH response < or = 1 mU/l, group 1; > 1-3 mU/l, group 2; > 3-6 mU/l, group 3; > 6-8.9 mU/l, group 4).

RESULTS

The IGF-I SDS (mean value +/- SD) in the CO group (n = 63) as a whole was significantly lower than that found in the AO group (n = 83) (-3.7 +/- 2.8 vs.-1.55 +/- 2.2, respectively; P < 0.0001). Despite this, there was no significant difference in the peak GH response to an ITT between the two cohorts (2.8 +/- 2.3 mU/l in the AO cohort and 2.6 +/- 2.2 mU/l in the CO cohort; P = 0.5). When the cohorts were subdivided by severity of GH deficiency, there remained a significant difference in IGF-I SDS in groups 1 (P < 0.0001), 2 (P = 0.05) and 3 (P < 0.05), but there was no significant difference between the AO and CO cohorts in group 4. The peak GH response to an ITT was similar in the AO and CO cohorts in all groups (P = 0.8, 0.8, 0.9 and 0.3 in groups 1-4, respectively). Although increasing severity of hypopituitarism was associated with a decline in IGF-I SDS in the CO cohort (P < 0.01), this was not the case in the AO cohort (P = 0.3).

CONCLUSION

These data support the hypothesis that there is an innate difference between adult patients with either CO or AO GH deficiency that cannot be explained solely by variation in the severity of GH deficiency. A possible explanation is that childhood GH deficiency programmes the subsequent relationship between GH and IGF-I in adult life or that the body composition changes, which are more severe in AO GH deficiency, influence IGF-I status.

Childhood-onset growth hormone (GH) deficiency in adult life

Over the last decade GH replacement therapy for adults has progressed in status from research study to a mainstream clinical indication. An area ripe for further research, however, is the difference between adults who developed GHD before and after completion of growth and puberty. That differences exist, not only in aetiology, but also in phenotype and response to GH therapy is clear. However, whether these differences are intrinsic to the timing of onset of GHD, or related to secondary factors including the method of assessment or dose of GH employed is uncertain. This chapter discusses the current state of knowledge in this area and poses further questions, not only for the researcher attempting to understand the mechanisms underlying these differences, but also for the physician seeking to ameliorate the impact of GHD in patients who acquired GHD in childhood.

The growth hormone (GH)-insulin-like growth factor axis during testosterone replacement therapy in GH-treated hypopituitary males

Several studies suggest a direct effect of sex steroids on insulin-like growth factor-I (IGF-I) production. Oestrogen has been hypothesized directly to inhibit hepatic IGF-I production, but the role of androgens is not clarified. We aimed to investigate whether testosterone exerts a pituitary-independent effect on IGF-I and related parameters. Eight adult hypopituitary men (39.9 +/- 5.7 years) receiving growth hormone (GH) and testosterone replacement therapy (250 mg testosterone enantate every fourth week) participated in this prospective study. Frequent blood samples were drawn over a 5 week period in relation to two testosterone injections. Mean baseline IGF-I levels were 352 +/- 135 microg/L, and they remained unaltered during the study period (analysis of variance (ANOVA), P = 0.88). Free IGF-I levels did not change either (ANOVA, P = 0.35). Serum IGF binding protein-3 (IGFBP-3) and acid-labile subunit decreased (ANOVA, P = 0.04 and P = 0.02 respectively) but post hoc analysis did not reveal a particular difference between days. IGFBP-1 increased following testosterone administration (ANOVA, P = 0.05), whereas GH binding protein levels tended to decrease following testosterone administration (ANOVA, P = 0.08). Prostate-specific antigen tended slightly to increase after each testosterone injection (ANOVA, P = 0.08, post hoc, NS). We conclude that major changes in total IGF-I are not induced during conventional intramuscular testosterone replacement in GH-treated hypopituitary males, suggesting that testosterone effects on IGF-I are likely to be secondary to a stimulation of endogenous GH release.

Energy balance and cancer: the role of insulin and insulin-like growth factor-I

Recent theories propose that a Western lifestyle may increase cancer risk through alterations in the metabolism of insulin and insulin-like growth factors (IGF: McKeown-Eyssen, 1994; Giovannucci, 1995; Kaaks, 19%; Werner & LeRoith, 1996). Insulin regulates energy metabolism, and increases the bioactivity of IGF-I, by enhancing its synthesis. and by decreasing several of its binding proteins (IGFBP; IGFBP-1 and -2). Insulin and IGF-I both stimulate anabolic processes as a function of available energy and elementary substrates (e.g. amino acids). The anabolic signals by insulin or IGF-I can promote tumour development by inhibiting apoptosis, and by stimulating cell proliferation. Furthermore, both insulin and IGF-I stimulate the synthesis of sex steroids, and inhibit the synthesis of sex hormone-binding globulin (SFIBG), a binding protein that regulates the bioavailability of circulating sex steroids to tissues. The present paper reviews epidemiological findings relating the risk of cancers of the colo-rectum, pancreas, breast, endometrium and prostate to body size (obesity, height) and physical activity, and discusses the relationships between obesity and physical activity and plasma levels of insulin, IGF-I and IGFBP. Subsequent sections review epidemiological findings relating cancer risk to indices of chronic hyperinsulinaemia, and to plasma levels of IGF-I and IGFBP. Conclusions are that chronic hyperinsulinaemia may be a cause of cancers of the colon, pancreas and endometrium, and also possibly of the breast. On the other hand, elevated plasma IGF-I, as total concentrations or relative to levels of IGFBP-3, appears to be related to an increased risk of prostate cancer, breast cancer in young women, and possibly cob-rectal cancer. For cancers of the endometrium, breast and prostate, these findings are discussed in the context of relationships between insulin and IGF-I and levels of bioavailable sex steroids.

Evaluation of the applicability of HRT as a preservative of muscle strength in women

OBJECTIVES

To review the studies that have been undertaken on the effects of postmenopausal hormone replacement therapy (HRT); especially oestrogen (+progestin) regimens on the preservation of muscle strength. Current knowledge of the mechanisms and actions of steroid- and sex hormones on skeletal muscle tissue will be used in an attempt to clarify the mechanism of action of a possible effect. The objective is to arrive at an agreement on whether or not postmenopausal oestrogen administration has a positive influence on skeletal muscle tissue.

METHODS

Peer-reviewed publications were assessed.

RESULTS

An age-related decrement in muscle strength can be found in both men and women. However, in women, an extra decline can be observed around the time of menopause. A possible relationship between the additional diminution in muscle strength and altered hormone concentrations after the onset of menopause has been suggested. Since women nowadays spend one-third of their life postmenopausal, it is extremely important to keep the decline in muscle mass as small as possible. Besides the continuation of a physically active lifestyle, HRT was suggested to serve as a protective mechanism. Although, the usefulness of HRT as a preservative of muscle strength appeared controversial.

CONCLUSIONS

Skeletal muscle strength is sensitive to training up to a high age, though continuation of physical activity does not appear to protect skeletal muscles completely from age-related decrements. Therefore, the development of another preventive method would be useful. Considering the present knowledge it has all the hallmarks that HRT can be a useful tool in the maintenance of muscle strength in postmenopausal women. None the less, further research is necessary to endorse this theory.

The negative association between serum free testosterone and leptin is dependent on insulin-like growth factor-binding protein 1 in healthy young and middle-aged men

OBJECTIVE

Previous studies have shown that serum levels of testosterone correlate negatively with leptin and positively with insulin-like growth factor binding protein 1 (IGFBP-1). The present study examined whether these associations are linked.

DESIGN AND PATIENTS

The association between serum levels of IGFBP-1, free testosterone and insulin on one hand and leptin on the other hand were investigated in 38 healthy men with a median age of 48 years (range 23-62 years).

RESULTS

Univariate analyses revealed that serum levels of leptin correlated negatively with serum free testosterone (r = - 0.42, P = 0.008) and with serum IGFBP-1 (r = - 0. 45, P = 0.005) and positively with body mass index (BMI; r = 0.46, P = 0.003) and serum insulin (r = 0.45, P = 0.004). Serum free testosterone correlated with IGFBP-1 (r = 0.42, P = 0.008) but not with serum insulin (r = - 0.08, ns). The correlations between leptin and free testosterone and between leptin and IGFBP-1 remained significant after adjustement for the influences of BMI and insulin. Forward stepwise multiple regression when BMI, insulin, testosterone and IGFBP-1 were entered in a model as independent variables and leptin as the dependent variable showed that BMI and IGFBP-1 were independent predictors of circulating leptin. These two parameters yielded an r 2 of 0.38, thereby together explaining approximately 40% of serum leptin.

CONCLUSION

Serum levels of free testosterone and IGFBP-1 correlate negatively with serum leptin in healthy nonobese men but this influence is dependent on the influence of IGFBP-1. The study therefore suggests an important impact of IGFBP-1 on the regulation of circulating leptin in young and middle-aged men.

Declining gonadal function in elderly men

Ageing in men is accompanied by a progressive decline of gonadal function with, in particular, a decline of total and free testosterone (T) plasma levels resulting in a significant proportion of elderly men over age 60 years presenting with subnormal T levels compared with the levels in young adults. A great interindividual variation in T levels is observed in elderly men, a variability explained in part by physiological variables and differences in life style, while associated acute or chronic diseases may accentuate the age-related decline of T levels. The progressive decrease of plasma T levels has been shown to result from both primary testicular changes and altered neuroendocrine regulation of Leydig cell function. At present, little is known about the clinical relevance of the relative hypoandrogenism of elderly men and there is an urgent need for more longitudinal studies, which may clarify a possible role of decreased T levels in the modulation of the clinical consequences of ageing in men. In view of the lack of relevant controlled clinical trials having careful assessment of the risks and benefits of androgen replacement therapy in elderly men, this treatment should be reserved for selected patients with clinically and biochemically manifest hypogonadism, after careful screening for contraindications.