Receptors for insulin-like growth factors and growth effects of multiplication-stimulating activity (rat insulin-like growth factor II) in rat embryo fibroblasts

Levels of multiplication-stimulating activity (MSA) in fetal rat serum are high (2-4 micrograms/ml), suggesting that MSA may have a role in fetal growth. We now demonstrate that fibroblasts derived from rat embryos (REFs) have specific MSA receptors and respond to MSA with increased DNA synthesis. Two types of insulin-like growth factor (IGF) receptors were demonstrated by competitive binding of radioiodinated MSA, IGF-I, and IGF-II and by chemical cross-linking of [125I]iodo-MSA and [125I]iodo-IGF-I to REFs. One type of receptor (mol wt, 260,000 under reducing conditions) did not interact with insulin, and another type of receptor (mol wt, 130,000, under reducing conditions) was recognized by insulin. Scatchard analysis of [125I]iodo-MSA binding data was consistent with one class of noninteracting binding sites. A biological response of MSA, increased DNA synthesis, was demonstrated with autoradiography in REFs. During a 16-hr incubation, DNA synthesis was stimulated by normal rat serum, and platelet-poor plasma plus platelet-derived growth factor (PDGF), but not by serum from hypophysectomized (hypox) rats or hypophysectomized (hypox) platelet-poor plasma plus PDGF. However, when MSA was added to hypox serum or to hypox platelet-poor plasma plus PDGF, DNA synthesis was stimulated to the level achieved by normal rat serum. By contrast, during a longer cell multiplication experiment, REFs grew equally well in normal or hypox rat serum, raising the possibility that REFs may produce a MSA-like factor.     

Structural basis for the inhibition of insulin-like growth factors by insulin-like growth factor-binding proteins

Insulin-like growth factor-binding proteins (IGFBPs) control bioavailability, activity, and distribution of insulin-like growth factor (IGF)1 and -2 through high-affinity IGFBP/IGF complexes. IGF-binding sites are found on N- and C-terminal fragments of IGFBPs, the two conserved domains of IGFBPs. The relative contributions of these domains to IGFBP/IGF complexation has been difficult to analyze, in part, because of the lack of appropriate three-dimensional structures. To analyze the effects of N- and C-terminal domain interactions, we determined several x-ray structures: first, of a ternary complex of N- and C-terminal domain fragments of IGFBP4 and IGF1 and second, of a "hybrid" ternary complex using the C-terminal domain fragment of IGFBP1 instead of IGFBP4. We also solved the binary complex of the N-terminal domains of IGFBP4 and IGF1, again to analyze C- and N-terminal domain interactions by comparison with the ternary complexes. The structures reveal the mechanisms of IGF signaling regulation via IGFBP binding. This finding supports research into the design of IGFBP variants as therapeutic IGF inhibitors for diseases of IGF disregulation. In IGFBP4, residues 1-38 form a rigid disulphide bond ladder-like structure, and the first five N-terminal residues bind to IGF and partially mask IGF residues responsible for the type 1 IGF receptor binding. A high-affinity IGF1-binding site is located in a globular structure between residues 39 and 82. Although the C-terminal domains do not form stable binary complexes with either IGF1 or the N-terminal domain of IGFBP4, in the ternary complex, the C-terminal domain contacts both and contributes to blocking of the IGF1 receptor-binding region of IGF1.     

Receptors for insulin-like growth factors I and II: autoradiographic localization in rat brain and comparison to receptors for insulin

Receptors for insulin-like growth factor I (IGF-I) in rat brain were visualized using autoradiography with [125I]IGF-I. The binding of the labeled peptide was competed for fully by high concentrations of unlabeled IGF-I. At intermediate concentrations of unlabeled peptide the binding of [125I]IGF-I was competed for by unlabeled IGF-I more effectively than by IGF-II or insulin, which is typical of receptors for IGF-I. Essentially every brain section shows specific binding of IGF-I, and the pattern of binding of IGF-I to its receptors correlated well with the cytoarchitectonic structures. In parallel studies we showed that [125I]IGF-II was bound to tissue sections of rat brain and that the binding was competed for by an excess of unlabeled IGF-II. However, intermediate concentrations of unlabeled peptides gave inconclusive results. To confirm that the binding of [125I]IGF-II was to IGF-II receptors, we showed that antibodies specific for the IGF-II receptor inhibited the binding of labeled IGF-II. Furthermore, the binding of the antibody to regions of the brain section, visualized by the application of [125I]protein-A, gave patterns indistinguishable from those obtained with [125I]IGF-II alone. Again, the binding was very widely distributed throughout the central nervous system, and the patterns of distribution corresponded well to the underlying neural structures. Densitometric analysis of the receptors enabled us to compare the distribution of IGF-I receptors with that of IGF-II receptors as well as retrospectively with that of insulin receptors.     

Receptors for insulin-like growth factor-I in plasma membranes isolated from bovine mesenteric arteries

Binding of IGF-I to plasma membranes from bovine mesenteric arteries was studied. The maximal specific binding of IGF-I was found to be 7.4 +/- 1.7% of total 125I-IGF-I added to the incubation medium. Unlabelled IGF-I displaced 125I-IGF-I with an IC50 value of 0.5 nmol/l and a maximal displacement of 64.2 +/- 2.8% of total binding. The potency of insulin to displace 125I-IGF-I was 100-1000-fold lower. Cross-linking of 125I-IGF-I to the receptor with disuccinimidyl suberate, followed by SDS-polyacrylamide gel electrophoresis under reducing conditions showed an IGF-I binding protein with a molecular weight of 146,000 Dalton. In summary, we have shown the presence of receptors for IGF-I in plasma membranes isolated from macrovessels. The binding characteristics and the size of the binding unit were found to be similar to those of the IGF-I receptor found in cultured vascular smooth muscle cells. Furthermore, insulin at high concentrations was found to interact with the IGF-I receptor.     

Insulin, insulin-like growth factors and neoplasia

Over the past decade, dozens of epidemiological studies and laboratory experiments have provided evidence for relationships between insulin-like growth factor (IGF) physiology and neoplasia. Population studies provide evidence for a modestly increased risk of a subsequent cancer diagnosis in subjects with IGF-I levels at the high end of the broad normal range, as compared to those at the low end of the normal range. At the cellular level, IGF-I receptor signalling has been shown to play an important role in facilitating the transforming action of a variety of oncogenes. Reducing receptor function with anti-receptor antibodies or specific tyrosine kinase inhibitors reduces the proliferation of many cancers in vitro and in vivo. At present, clinical relevance of the relationship between circulating IGF-I level and cancer risk is limited, but in terms of experimental therapeutics, many clinical trials have been initiated to investigate the possibility that the paradigm of hormonal treatment of cancer may be extended from targeting gonadal steroids to targeting the growth hormone-IGF-I axis.     

Receptors for insulin and insulin-like growth factor in cultured arterial smooth muscle cells depend on their growth state

The binding of 125I-labelled insulin and 125I-labelled insulin-like growth factor (IGF) to cultured arterial smooth muscle cells from rats was studied during various growth states of the cells. The level of binding of 125I-labelled insulin to the cells was low in growing cells and high in stationary cells. The level of 125I-labelled IGF binding to the cells was high in growing cells and low in stationary cells. In addition, the effect of unlabelled IGF and insulin on the binding of both 125I-labelled hormones to the cells was examined during various growth states. In growing cells insulin displaced 125I-labelled insulin from its binding sites; IGF competed weakly with 125I-labelled insulin for the binding sites. In parallel, IGF displaced 125I-labelled IGF binding whereas insulin competed weakly with 125I-labelled IGF for the binding sites. In stationary cells both hormones displaced 125I-labelled IGF binding. Insulin-like growth factor also displaced 125I-labelled insulin binding whereas insulin could not significantly displace 125I-labelled insulin from the binding sites. Insulin only competed with 125I-labelled insulin for the binding sites after removal of the fetal calf serum from the culture medium.     

Inhibition of insulin degradation by insulin-like growth factors

The effect of insulin-like growth factors (IGF 1 and IGF 2) on insulin degradation was studied with the use of a preparation of insulin protease from rat skeletal muscle. Insulin, IGF 1 and IGF 2 inhibited 125I-insulin degradation by this enzyme. IGF 2 was the most potent inhibitor and IGF 1 was the least potent. These results are similar to what has been reported previously for the insulin-degrading activity in the serum of a diabetic patient who was resistant to sc and im insulin. Insulin protease also degraded 125I-iodo IGF 1 and 125I-iodo IGF 2. 125I-iodo IGF 2 was degraded more rapidly than was 125I-iodo IGF 1. 125I-iodoinsulin was degraded more rapidly than 125I-iodo IGF 2. With all three peptides, immunoprecipitation was a more sensitive measure of degradation than was trichloroacetic acid precipitation. The results suggest that insulin protease may be responsible for the degradation of insulin-like growth factors as well as of insulin.     

Therapeutic applications of the insulin-like growth factors.

The potential therapeutic applications of the insulin-like growth factors (IGFs) are broad. This review focuses on treatment of humans with recombinant human IGF-I (rhIGF-I), and with a rhIGF-I/IGF binding protein-3 (IGFBP-3) complex. Several groups of patients have been treated effectively, including individuals with growth hormone insensitivity syndrome (GHIS) secondary to GH receptor deficiency, to IGF-I gene deletion, or to defects in GH signal transduction pathways, patients with type 1 and type 2 diabetes mellitus, or individuals with severe insulin resistance syndromes. In each of these conditions rhIGF-I therapy has been demonstrated to be of clear clinical benefit. Other conditions, which may potential targets for therapy with rhIGF-I or rhIGF-I/IGFBP-3, include chronic inflammatory or nutritional disorders such as Crohn's disease, juvenile chronic arthritis, or cystic fibrosis. Therapy with IGFs has not been attempted in these disorders yet, in part because of lack of adequate supplies. Recently, the newly developed rhIGF-I/IGFBP-3 complex has been used in early clinical studies. Pharmacokinetic analyses in patients with diabetes mellitus and GHIS have suggested that a more physiological profile of serum IGF-I results. Improved glycaemic control has been reported in type 1 and type 2 diabetes in adults. A therapeutic trial in na?ve children with GHIS is currently under way.     

Diurnal rhythm of growth hormone-independent binding protein for insulin-like growth factors in human plasma

An antibody raised against the major insulin-like growth factor (IGF)-binding protein in amniotic fluid (BP-28) was used to measure the levels of a cross-reacting protein in human plasma by RIA. Plasma BP-28 immunoreactivity had an apparent mol wt of 35,000 by high performance permeation chromatography. Sampled hourly for 12- or 24-h periods in 15 children with a wide range of GH secretory activity, plasma BP-28 levels showed a marked diurnal cycle, rising 10- to 20-fold between 2400 and 0600 h to a peak of 50-500 micrograms/L, then falling to basal levels (0-40 micrograms/L) by 1200 h. Plasma GH levels were measured at 20-min intervals in the same subjects. Neither peak nor basal BP-28 levels were significantly associated with chronological age, bone age, mean or peak nocturnal GH secretion, relative height, or relative growth velocity in tall, normal, short, or GH-deficient children. Plasma proteins measured in a RIA for 53,000 mol wt GH-dependent IGF-binding protein (BP-53) did not vary diurnally. The IGF-binding activity of plasma BP-28, measured by incubating plasma with IGF tracer and precipitating the BP-28-IGF complex with anti-BP-28 antiserum, closely paralleled the morning rise in BP-28 immunoreactivity. Immunoprecipitable BP-28 bound both IGF-I and IGF-II tracers, with a clear preference for IGF-I, and unlabeled IGF-I was more effective than IGF-II in displacing either tracer IGF. We conclude that plasma BP-28 levels in children have a marked diurnal rhythm which is unrelated to GH secretory activity.     

The effects of insulin-like growth factors on tumorigenesis and neoplastic growth

Several decades of basic and clinical research have demonstrated that there is an association between the insulin-like growth factors (IGFs) and neoplasia. We begin with a brief discussion of the function and regulation of expression of the IGFs, their receptors and the IGF-binding proteins (IGFBPs). A number of investigational interventional strategies targeting the GH or IGFs are then reviewed. Finally, we have assembled the available scientific knowledge about this relationship for each of the major tumor types. The tumors have been grouped together by organ system and for each of the major tumors, various key elements of the relationship between IGFs and tumor growth are discussed. Specifically these include the presence or absence of autocrine IGF-I and IGF-II production; presence or absence of IGF-I and IGF-II receptor expression; the expression and functions of the IGFBPs; in vitro and in vivo experiments involving therapeutic interventions; and available results from clinical trials evaluating the effect of GH/IGF axis down-regulation in various malignancies.     

Production of insulin-like growth factors by ovarian granulosa cells

Evidence for ovarian secretion of somatomedins or insulin-like growth factors (IGF's) was generated by two approaches. First, porcine granulosa cells were shown to produce IGF's and an IGF-binding protein under serum-free conditions in vitro. The ovarian IGF's were recognized in two competitive binding assays specific for IGF's, a RIA using antibodies to human IGF-I and a radioreceptor assay using rat liver plasma membranes. IGF secretion was maintained for at least 10 days in culture. Second, ovarian production of IGF's in vivo was suggested by studies which showed that IGF levels in follicular fluid from preovulatory follicles were significantly greater than those in either serum or immature follicles. In contrast, similar low levels of insulin were observed in the follicles and serum. In conjunction with previous evidence of IGF action on granulosa cells, the present studies suggest the possibility of an autocrine role of IGF's in regulating follicular growth and development.     

Effects of insulin-like growth factors on chick embryo hepatocytes

Biological effects of insulin-like growth factors (IGF) I and II on primary cultures of chick embryo liver cells have been investigated and compared 1) with the biological effect of insulin and 2) with competitive binding of the three hormones to their respective binding sites. IGF I and II stimulate the incorporation of D[U-14C]-glucose into liver cell glycogen in a time- and dose-dependent manner, but with a 5-10-fold lower potency than insulin. Both IGFs also lead to enhanced incorporation of 5-[3H]uridine and L[U-14C]valine into trichloroacetic acid (TCA) insoluble material and to activation of ornithine decarboxylase activity. Their potency in stimulating RNA synthesis and ornithine decarboxylase activity is comparable to that of insulin. Protein synthesis is maximally stimulated at 3 nM by all three hormones. In the competitive binding studies, IGF I and II are 10-fold less potent than insulin in competing for [125I]insulin binding, but 100-fold more potent than insulin in competing for [125I]IGF I or II binding. These studies show that IGF I and II stimulate the same metabolic indices as insulin in the chick embryo liver. By comparing these biological effects with competitive binding data it appears that IGFs act on glucose metabolism in the chick embryo liver via the insulin receptor, whereas stimulation of growth indices by IGFs and insulin appears to be mediated by their own specific receptors.     

Associations of insulin-like growth factors, insulin-like growth factor binding proteins and acid-labile subunit with coronary heart disease

OBJECTIVE: IGFs and their binding proteins (IGFBPs) are produced both systemically and locally by cells of the cardiovascular system. As growth promoters, they may play a role in atherosclerosis. DESIGN: Case-control, cross-sectional. PATIENTS: A total of 95 nondiabetic male patients with coronary heart disease (CHD) and 92 probands from the Prospective Cardiovascular Munster (PROCAM) who were below the age of 60 years and matched by age, body mass index (BMI) and smoking habits. MEASUREMENTS: We analysed the strength and independence of associations of angiographically assessed presence of CHD with BMI, systolic and diastolic blood pressure, total, high-density lipoprotein (HDL) and LDL cholesterol, triglycerides, lipoprotein(a), apolipoproteins A-I and B, total and free IGF-I, IGF-II, IGFBP-1, IGFBP-3, IGFBP-5, acid-labile subunit (ALS), insulin, C-peptide, testosterone, DHEAS and sex hormone binding globulin. RESULTS: Using multivariate statistical analysis, the presence of CHD had significant positive associations with total IGF-I, IGFBP-5, ALS and IGFBP-3. These associations were independent of each other as well as of traditional risk factors, insulin and sex hormones. CONCLUSION: These observations may indicate a pathogenetic role of the GH/IGF axis in coronary atherosclerosis.     

重型病毒性肝炎患者生长激素-胰岛素样生长因子轴的临床研究

目的研究重型病毒性肝炎患者GH-IGF轴的变化及其临床意义。方法重型病毒性肝炎患者18例,其中急性重型2例,亚急性重型5例,慢性重型11例;正常对照20例。ELISA法测定血清GH、IGF-1、IGFBP1及IGFBP3,全自动生物化学分析仪常规方法测定肝脏生物化学指标。结果重型肝炎患者血清IGF-1、IGFBP3水平明显降低［(5.5±6.2)μg/ml对(17.6±7.0)μg/ml,(2.4±1.3)μg/ml对(9.4±1.7),P＜0.001］。GH、IGFBP1水平增高［(9.1±12.4)ng/ml对(1.6±2.4)ng/ml,P＜0.05;(67.9±50.2)ng/ml对(45.8±33.1)ng/ml,P＜0.01)］。血清IGF-1与IGFBP3呈正相关(r＝0.91,P＜0.001);IGF-1降低与重型肝炎患者预后密切相关(P＜0.001)。IGF-1＜10μg/ml,预测死亡的符合率为90%;IGF-1＞10μg/ml,预测存活的符合率为89.5%。结论重型病毒性肝炎患者GH-IGF轴发生显著异常变化,GH增高与IGF-1水平降低相矛盾,提示重型病毒性肝炎患者存在生长激素抵抗。血清IGF-1水平可作为预测重型肝炎患者预后的指标。     

Small stature and insulin-like growth factors: prolonged treatment of mini-poodles with recombinant human insulin-like growth factor I

The short stature of mini-poodles is associated with low serum levels of IGF-I. Standard poodles are taller and have considerably higher serum levels of IGF-I. Low IGF-I serum levels may be a symptom or the cause of small stature. We, therefore, undertook a study in which serum IGF-I levels of mini-poodles were elevated over a prolonged period of time by a constant infusion of rhIGF-I and the growth rate of the mini-poodles was followed. We infused four mini-poodles from day 91 to day 221 of age with 6 mg/day of recombinant human insulin-like growth factor I (rhIGF-I). Serum levels of IGF-I rose from about 160 to about 500 micrograms/l. Blood glucose remained within normal limits. Stimulation tests with clonidine and with GHRH revealed suppression of endogenous GH secretion during the IGF-I infusion. Serum levels of IGF-II and of creatinine were lower in the IGF-I-infused animals. Radial length and body weight did not increase to a greater extent in the IGF-I infused dogs than in controls. However, 'adapted body mass index' (aBMI = gram body weight/(mm radial length)2) decreased in each of the IGF-I infused animals, whereas it increased in each of the control dogs (p less than 0.05). We conclude that long-term infusion of IGF-I does not stimulate growth in young mini-poodles, but may change body composition.     

An autocrine/paracrine role for insulin-like growth factors in the regulation of human placental growth

Tissue derived from preterm (9-19 weeks gestation) and term (38-41 weeks gestation) human placentae were examined for their ability to synthesize and secrete insulin-like growth factors (IGFs) in organ culture. IGF-I was measured by a specific RIA, and IGF-II by a rat placental membrane radioreceptor assay. First, explants of placental tissue were maintained in organ culture. These explants secreted immunoreactive IGF-I (IR-IGF-I). There were no differences in the IR-IGF-I content of media conditioned by term and preterm placentae under these conditions. The similarity of this material to authentic human IGF-I was supported by parallel displacement in a specific RIA and coelution during Sephadex G-50 gel filtration. Second, monolayer cultures of fibroblasts from normal human preterm placentae (15-19 weeks gestation) were established. Confluent monolayers of these fibroblasts secreted IR-IGF-I (3-10 pg/10(5) cells X 40 h). IR-IGF-I secretion was reversibly inhibited by 5.3 microM cycloheximide, suggesting that the IR-IGF-I was the result of de novo protein synthesis. IR-IGF-I secretion was stimulated 5-fold by platelet-derived growth factor (0.6 U/ml). The response of monolayers of placental fibroblasts to IGF-I also was tested. IGF-I stimulated alpha-[3H]aminoisobutyric acid transport in these fibroblasts, with half-maximal stimulation occurring at 2-3 ng/ml. Stimulation of alpha-[3H]aminoisobutyric acid uptake by IGF-I correlated with specific binding of [125I]iodo-IGF-I. Half-maximal inhibition of [125I]iodo-IGF-I binding occurred at 2-3 ng/ml IGF-I. Placental tissue also secreted IGF-II-like activity, as measured by radioreceptor assay. Media conditioned by placental explants contained 15-20 ng/mg protein X 48 h, and media conditioned by placental fibroblasts contained 3-7 ng/10(5) cells X 40 h IGF-II determined by radioreceptor assay. These data support the hypothesis that the human placenta produces IGFs (IGF-II and/or IGF-I) that act locally to regulate placental growth.     

Receptors for insulin-like growth factor II in the rat uterus: characterization and variation throughout the estrus cycle

This study was undertaken to identify uterine insulin-like growth factor II receptors and examine the regulation of these receptor levels throughout the estrus cycle. We have demonstrated IGF-II receptors in crude uterine membranes by binding and cross-linking experiments. IGF-II binding to the rat uterine membranes displayed time and temperature dependence and maximum binding was achieved by 2 h at 22 degrees C. Uterine IGF-II binding sites were specific for binding IGF-II peptide and demonstrated negligible binding affinity for IGF-I and no affinity for insulin. The specific anti-IGF-II receptor antibody, R-II-PAB1, blocked the specific [125I]IGF-II binding to uterine membranes in a dose-dependent manner. The characteristics of uterine IGF-II receptor are similar to those reported for other tissues, with a single class of high-affinity binding sites with an apparent dissociation constant of 1.2 +/- 0.5 nmol/l and Beta max of 2.65 +/- 0.41 pmol/mg protein. Affinity cross-linking experiments indicated that the specific binding of [125I]IGF-II in the uterus is associated with a single band of protein with a mol wt of 250 kD. In mature cycling rats, the proestrus uterus had the lowest level of [125I]IGF-II binding per mg membrane protein, without changes in receptor affinity. However, because of greater yield of protein from proestrus uteri, the total [125I]IGF-II binding capacity of the uterus was similar to the other stages of the estrus cycle. These studies demonstrate the presence of authentic IGF-II receptors in the rat uterus and illustrate variations in the concentration of these receptors in the uterus throughout the estrus cycle.     

The presence of cation-dependent proteases for insulin-like growth factor binding proteins does not alter the size distribution of insulin-like growth factors in pregnancy

OBJECTIVE: The aim was to investigate the sera of pregnant women for the presence of specific proteases for insulin-like growth factor binding proteins (IGFBPs) and to determine the effect of these on the distribution of IGFs in the circulation. DESIGN: The method used was the chromatographic and electrophoretic analysis of patients' serum. PATIENTS: Sera were examined from normal women during pregnancy: first trimester (n = 4), second trimester (n = 4) and third trimester (n = 10). Eight women with Type I diabetes in the third trimester were also studied along with sera from ten normal adult volunteers. MEASUREMENTS: Circulating IGF-I and IGF-II levels were measured by RIA and their distribution examined by gel filtration. The pattern and stability of the IGFBPs was investigated by Western ligand blotting. RESULTS: A marked reduction in the serum levels of IGFBP-2, IGFBP-3 and IGFBP-4 on Western ligand blotting, which was associated with the presence of three independent, cation-dependent proteases that were specific for different IGFBPs, was found in late pregnancy. Gel filtration of third trimester serum revealed most of the IGF-I to be present in a complex larger than 130 kDa, with a similar distribution to that found in serum of non-pregnant women. The enzymatic modification of the binding proteins made apparent by the decrease in binding protein bands on Western ligand blotting of preincubated samples had no effect on the distribution of IGF-I following size fractionation. CONCLUSIONS: There appear to be at least three independent enzymes that are induced or activated during pregnancy to modify IGFBP-2, IGFBP-3 and IGFBP-4 sufficiently to prevent their detection by ligand blotting. However, this enzymatic processing does not alter the distribution of IGFs, suggesting that the altered binding proteins are still able to carry IGFs but with reduced affinity. Such an alteration in the carrying mechanism of IGFs may have profound effects upon the bioavailability of the IGFs to the maternal tissues and contribute to the altered metabolic demands of pregnancy.     

Growth hormone, insulin-like growth factors, and the skeleton

GH and IGF-I are important regulators of bone homeostasis and are central to the achievement of normal longitudinal bone growth and bone mass. Although GH may act directly on skeletal cells, most of its effects are mediated by IGF-I, which is present in the systemic circulation and is synthesized by peripheral tissues. The availability of IGF-I is regulated by IGF binding proteins. IGF-I enhances the differentiated function of the osteoblast and bone formation. Adult GH deficiency causes low bone turnover osteoporosis with high risk of vertebral and nonvertebral fractures, and the low bone mass can be partially reversed by GH replacement. Acromegaly is characterized by high bone turnover, which can lead to bone loss and vertebral fractures, particularly in patients with coexistent hypogonadism. GH and IGF-I secretion are decreased in aging individuals, and abnormalities in the GH/IGF-I axis play a role in the pathogenesis of the osteoporosis of anorexia nervosa and after glucocorticoid exposure.