Systemic and renal growth hormone-IGF1 axis involvement in a mouse model of type 2 diabetes

AIMS/HYPOTHESIS

In previous studies we have shown a significant involvement of the growth hormone (GH)-IGF axis in animal models of type 1 diabetes mellitus, but the role of this endocrine system in type 2 diabetes mellitus is less well characterised. We therefore examined the endocrine and renal GH-IGF axis changes in db/db mice, a model of type 2 diabetes mellitus and nephropathy.

MATERIALS AND METHODS

Obese and lean animals were followed, beginning at hyperglycaemia onset, for 4 weeks. Albuminuria and creatinine clearance, as well as kidney and glomerular morphology were assessed. Tissue protein levels were determined by western blotting and mRNA levels by RT-PCR.

RESULTS

Serum GH and IGF1 levels immediately prior to killing were decreased and liver mRNA levels of insulin-like growth factor binding protein 1 (Igfbp1) were increased in obese animals. Kidney weight was increased in obese animals, associated with hyperfiltration, albuminuria and glomerular hypertrophy. Administration of a somatostatin analogue (PTR-313) did not improve any of these parameters of diabetic renal involvement. Renal Igf1 mRNA was decreased and renal Igfbp1 mRNA and protein were significantly increased in obese animals. Renal insulin-driven levels of phosphorylated forkhead box O1 (FOXO1) were decreased in obese animals.

CONCLUSIONS/INTERPRETATION

Diabetic db/db mice show significant renal changes (and IGFBP1 renal accumulation), similar to the findings in models of type 1 diabetes mellitus. A decreased signalling through the insulin receptor and decreased FOXO1 phosphorylation may allow Igfbp1 gene transcription. These renal changes are associated with low circulating IGF1 and GH levels and unchanged hepatic growth hormone receptor expression, unlike the condition in type 1 diabetes mellitus. This suggests that further GH inhibition to modulate renal complications in type 2 diabetes mellitus is not indicated.

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

Sex hormones may influence longitudinal growth, either indirectly, by affecting the growth-hormone-insulin-like growth factor I (IGF-I) axis, or directly, by affecting changes within the epiphyseal growth plate (EGP). The aim of the present study was to investigate the effects of letrozole, an aromatase inhibitor, on longitudinal growth and changes in the EGP in vivo. Eighteen peripubertal male mice were divided into three groups. The first group was killed at baseline, the second was injected with letrozole (Femara) s.c., 2 mg/kg body weight/day, for 10 days, and the third was injected with the vehicle alone. Serum testosterone levels were found to be significantly higher in the treated group than in the controls. Letrozole induced a significant increase in body weight, tail length and serum growth hormone level, but had no significant effect on the level of serum IGF-I. On histomorphometric study, there was a significant increase (12%) in EGP height in the treated animals compared with controls. Immunohistochemistry showed a 3.4-fold letrozole-induced increase in the proliferation of the EGP chondrocytes, as estimated by the number of proliferation cell nuclear antigen-stained cells, and a decrease in the differentiation of the EGP chondrocytes, as estimated by type X collagen staining. Letrozole did not interfere with type II collagen levels. The study group also showed a twofold increase in the number of IGF-I receptor-positive cells compared with controls. In conclusion, the aromatase inhibitor, letrozole, appears to increase the linear growth potential of the EGP in mice.

Leptin reverses the inhibitory effect of caloric restriction on longitudinal growth

Caloric imbalance, particularly in critical periods of growth and development, is often the underlying cause of growth abnormalities. Serum levels of leptin are elevated in obesity and are low in malnutrition and malabsorption. The aim of the present study was to determine whether leptin integrates energy levels and growth in vivo, as shown previously in our ex vivo experiments, even in the presence of caloric restriction. In the first part of the study, mice were divided into three groups. Two groups were fed ad libitum and received leptin or vehicle only, and the third group was pair-fed with the group injected with leptin to dissociate leptin's effect on growth from its effect on food consumption. Mice given leptin had a significantly greater tibial length than untreated pair-fed animals and a similar tibial length as control mice fed ad libitum despite their lower weight. In addition, leptin significantly increased the overall size of the epiphyseal growth plate by 11%. On immunohistochemistry and in situ hybridization studies, leptin stimulated both the proliferation and differentiation of tibial growth plate chondrocytes without affecting the overall organization of the plate. There was also a marked increase in the expression and level of IGF-IR. In the second part of the study, two groups of mice were fed only 60% of their normal chow; one was injected with leptin, and the other was injected with vehicle alone. Caloric deprivation by itself reduced serum levels of IGF-I by 70% and the length of the tibia by 5%. Leptin treatment corrected the fasting-induced growth deficiency, but further reduced the level of serum IGF-I. These results indicate that leptin stimulates growth even in the presence of caloric restriction independently of peripheral IGF-I.

Modulation of Brain Insulin-Like Growth Factor I (IGF-I) Binding Sites and Hypothalamic GHRH and Somatostatin Levels by Exogenous Growth Hormone and IGF-I in Juvenile Rats

The effect of exogenous growth hormone (GH) and insulin-like growth factor I (IGF-I) on brain IGF-I binding sites (IGF-IR), and on the levels of growth hormone-releasing hormone (GHRH) and somatostatin was studied in hypophysectomized and intact juvenile male rats. Animals were injected subcutaneously twice daily (n = 5 each) with recombinant GH (rGH) (2.5 U/kg per day) or rIGF-I (500 microg/kg per day). In the hypophysectomized rats, serum GH and IGF-I levels were markedly suppressed and IGF-I levels were partially restored by GH treatment. There was a significant increase in IGF-IR binding capacity in the IGF-I-treated hypophysectomized rats compared to the saline-treated hypophysectomized animals (150.61 +/- 45.66 vs 41.32 +/- 12.42 fmol/mg, p < 0.05) but no significant difference in IGF-IR mRNA levels. GHRH levels in the saline-treated hypophysectomized group were significantly lower than in the saline-treated intact rats (31.2 +/- 11.2 vs 140.6 +/- 48.1 pg/mg tissue, respectively, p < 0.01); no effect was induced by GH or IGF-I (37.5 +/- 26.8 and 53.8 +/- 22.5 pg/mg tissue, respectively). However, in the intact rats, GH and IGF-I injection led to a decrease in GHRH content, which was significant in the GH-treated compared to the saline-treated animals (33.1 +/- 16.2 vs 140.6 +/- 48.1 pg/mg tissue, p < 0.01). No difference was found in somatostatin levels between intact and hypophysectomized rats (631.2 +/- 81.2 and 625.0 +/- 62.5 pg/mg tissue, respectively). However, in the hypophysectomized animals, GH and IGF-I treatment induced a significant increase in somatostatin levels (1300 +/- 193.7 pg/mg tissue, p < 0.01, and 912.5 +/- 81.2 pg/mg tissue, p < 0.05, respectively). Our findings suggest that the bioavailability of exogenous IGF-I is greater than that of GH-stimulated endogenous IGF-I. Because IGF-I is a potent neurotrophic agent, this effect may have important implications for states of neurodegenerative diseases.

Effect of dehydroepiandrosterone and its sulfate metabolite on neuronal cell viability in culture

BACKGROUND

The neurosteroids dehydroepiandrosterone (DHEA) and its sulfated metabolite (DHEAS) have been reported to possess neuroprotective as well as anti-tumoral activity in vitro and in vivo.

OBJECTIVES

To compare the effect of the two neurohormones on cell viability in primary whole-brain fetal mouse culture and isolated neuronal culture, as well as in a human neuroblastoma cell line (SK-N-SH).

METHODS

Cell viability and cell proliferation were determined with the neutral red and 3H-thymidine uptake methods. Apoptosis in propidium iodide-stained neuroblastoma cells was determined using flow cytometry.

RESULTS

DHEA (1 nM-10 microM) decreased the viability of selected primary neuronal cells (33-95% after 24 and 72 hours) but not of whole-brain cultured cells (neuron + glia). DHEAS did not significantly modify cell viability in either primary culture. In a human neuroblastoma cell line, DHEA (1 nM-1 microM) decreased 3H-thymidine uptake (30-60%) and cell viability (23-52%) after 24 hours. DHEAS did not significantly modify, or only slightly stimulated, cell viability and uptake of 3H-thymidine (132% of controls). The combination of DHEA and DHEAS neutralized the toxic effect of DHEA in both primary neuronal culture and neuroblastoma cell line. Flow cytometric analysis of DNA fragmentation in neuroblastoma cells treated with 100 nM DHEA/DHEAS for 24 hours showed an increase in apoptotic events (31.9% and 26.3%, respectively, vs. control 2.54%).

CONCLUSIONS

Our results do not confirm a neuroprotective role for DHEA and suggest that DHEA and DHEAS have a differential role; DHEA possesses a neurotoxic (expressed only in isolated neurons) and anti-proliferative effect; DHEAS demonstrates only a slight neuroprotective effect.

Insights from animal models for growing intestinal neomucosa with serosal patching--a still untapped technique for the treatment of short bowel syndrome

The aim of surgical treatment of short bowel syndrome is to increase the intestinal absorptive capacity by increasing the area of absorption or by slowing intestinal transit. The use of serosal patching to grow new intestinal mucosa is a technique for enlarging the intestinal surface. The regenerated intestine develops by lateral ingrowth from the neighbouring mucosa and is functionally similar to normal intestinal mucosa. The present review summarizes the main contributions of the rabbit, the rat and the canine models used to date for growing neomucosa using the serosal patch technique, as well as examining the influence of some growth factors on the development of neomucosa.

Decreased insulin-like growth factor-I receptor sites on circulating mononuclear cells from children with acute leukemia

Insulin-like growth factor-I (IGF-I) is a known mitogen for various cell types, including those of the hematopoietic cell system. To study the role of IGF-I in the neoplastic process of leukemia in children, the authors have determined the number of IGF-I binding sites on circulating mononuclear cells of children with acute leukemia as compared to normal children, using binding assays. The IGF-I binding sites per cell on peripheral mononuclear cells of children with leukemia decreased compared to those of the control group (411 +/- 73 and 1334 +/- 227, respectively, p < .001), while their affinity increased (Kd = 0.14 +/- 0.04 and 0.43 +/- 0.16, respectively, p = .05). Furthermore, in the patients, the number of the IGF-I binding sites was significantly lower in the subgroup of the peripheral mononuclear cells, which included lymphocytes and monocytes, as compared to their number in the peripheral blast cells (254 +/- 43.6 and 536 +/- 98.6, respectively, p = .02). A significant reduction was found in serum GHBP levels in the patients as compared to the controls (28.21 +/- 1.93 and 35.83 +/- 2.90, respectively, p = .02), while serum IGF-I and growth hormone levels were similar in patient and control groups. These results suggest a possible involvement of IGF-I in childhood acute leukemia, but further studies are needed to establish whether IGF-I plays a role in this disease.

Changes in the growth hormone-IGF-I axis in non-obese diabetic mice

We investigated the changes in GH-IGF-I axis in non-obese diabetic (NOD)-mice, a model of insulin-dependent diabetes mellitus. Diabetic female NOD mice and their age- and sex-matched controls were sacrificed at 4, 14, 21 and 30 days (30d DM) after the onset of glycosuria. Serum GH levels increased and serum IGF-I levels decreased in the 30d DM group (182 +/- 32% and 45 +/- 24% of age-matched controls respectively, p < 0.05). Another group (30d DM + I) was given SC insulin, and its serum IGF-I levels remained decreased. Liver GH receptor (GHR) and GH binding protein (GHBP) mRNA levels, as well as liver membrane GH binding assays were deeply decreased in the 30d DM group in comparison to controls. GHR message and binding capacity remained decreased in the 30d DM + I group. Renal GHR mRNA was decreased at 21d DM but not at 14d DM, whereas GHBP mRNA remained unchanged throughout the experiment. In conclusion, increased serum GH levels are documented in NOD diabetic mice, similarly to the changes described in humans. The decrease in GHR levels and decreased serum IGF-I in spite of increased circulating GH suggest a state of GH resistance.

Development of hyperandrogenism during treatment with insulin-like growth factor-I (IGF-I) in female patients with Laron syndrome

OBJECTIVE

Patients with Laron syndrome (LS) can now be treated with recombinant IGF-I. We describe the development of androgenization during IGF-I treatment of female LS patients.

PATIENTS

Six female patients with LS--two clinically prepubertal (11.6 and 13.8 years of age) and four young adults (30 to 39 years old)--underwent long-term replacement treatment with recombinant IGF-I. The daily doses were 150 micrograms/kg/day by subcutaneous (s.c.) injection in the girls and 120 micrograms/kg/day in the adult women.

METHODS

Testosterone, delta 4-androstenedione, LH, FSH, insulin and IGF-I were determined by radioimmunoassay. Blood samples were obtained after an overnight fast before the IGF-I injection. Serum IGF-I was also determined 4 hours after the s.c. injections.

RESULTS

During IGF-I treatment, four out of the six patients (two girls and two adults) developed progressive clinical symptoms and signs of hyperandrogenism (oligo/amenorrhoea and acne). Laboratory determinations showed a significant elevation in serum testosterone, delta 4-androstenedione and LH/FSH ratio. The hyperandrogenism occurred concomitantly with an increase in IGF-I serum and a decrease in serum insulin concentrations. Reduction in IGF-I dose or interruption in IGF-I treatment restored androgen levels to normal values. At the same time, the acne and oligomenorrhoea resolved.

CONCLUSIONS

Overdosage of IGF-I can lead to androgenization, a previously undescribed undesirable effect of IGF-I. Long-term IGF-I treatment necessitates progressive adjustment of the IGF-I dose to avoid overtreatment.

Increased number of IGF-I receptors on erythrocytes of women with polycystic ovarian syndrome

OBJECTIVE

To test the hypothesis that insulin acts though ovarian IGF-I receptors to produce excessive amounts of androgens in polycystic ovarian syndrome (PCOS), by measuring the binding capacity of IGF-I receptors on erythrocytes and relating the findings to the degree of hyperandrogenism and hyperinsulinaemia.

DESIGN

A case-control study of IGF-I receptors on erythrocytes of women with PCOS and age- and weight-matched controls.

PATIENTS AND METHODS

IGF-I receptors on erythrocytes, serum levels of androgens, IGF-I, GH, basal insulin and insulin response during oral glucose tolerance test (oGTT) were measured after induced or spontaneous withdrawal bleeding in 10 women with PCOS and eight normo-ovulatory women.

RESULTS

An increased number of IGF-I receptors was found on erythrocytes of patients with PCOS compared with the controls (P < 0.01), irrespective of their body mass index. Serum IGF-I levels were similar in both groups. The degree of hyperinsulinaemia, provoked by oGTT, correlated positively with basal insulin (r = 0.69; P = 0.003), but not with the number of IGF-I receptors. However, the number of IGF-I receptors correlated positively with androstenedione (r = 0.54, P = 0.0018).

CONCLUSIONS

The findings in the present study that the number of IGF-I receptors and not the insulin levels correlate with serum androstenedione support the theory that the hyperandrogenism in PCOS is not a direct effect of the hyperinsulinaemia, but IGF-I mediated.

Lack of effect of methylphenidate on serum growth hormone (GH), GH-binding protein, and insulin-like growth factor I

The aim of this study was to assess the growth hormone (GH) axis in methylphenidate (MPH)-treated and untreated boys with attention-deficit and hyperactivity disorder (ADHD), by evaluating serum GH, GH-binding protein (GHBP) activity, and insulin-like growth factor I (IGF-I) levels as compared to age-matched normal controls. Blood samples were taken from 42 boys (aged 6-16 years) diagnosed as having ADHD according to DSM-III-R criteria and confirmed by using the Schedule for Affective Disorder and Schizophrenia for school-age children (K[Kiddle]-SADS). A total of 21 patients were treated with MPH (5-20 mg/day; 0.15-0.77 mg/kg/day), on a drug holiday protocol, for 1-36 months, and 21 were drug naive. A total of 46 age-matched normal boys at height and weight within normal range served as controls. No significant differences were detected between the MPH-treated ADHD children, the untreated ADHD children, and the control children on fasting serum GH levels, GHBP activity, or IGF-I levels. Active treatment with MPH, in ADHD children on a drug holiday protocol, does not cause changes in GH axis as manifested by normal values of GH, GHBP, and IGF-I.

Intronic mutation in the growth hormone (GH) receptor gene from a girl with Laron syndrome and extremely high serum GH binding protein: extended phenotypic study in a very large pedigree

Laron syndrome (LS) is a hereditary form of GH resistance due to molecular defects in the GH receptor (GHR). Most of the identified mutations are located in the extracellular domain of the receptor, resulting in a lack of serum GHBP in the majority of LS patients. We present an LS patient with supranormal levels of serum GHBP, in addition to 35 of her relatives. The proband is a 3.5 year-old Druse girl with severe short stature (height SDS -5.1), high GH (250 micrograms/l), low IGF-I (2.7 nmol/l) and IGFBP-3 (410 micrograms/l), both unresponsive to exogenous GH. The binding capacity of the serum GHBP was 22 nM (adult reference serum, 0.7 nM), with an affinity constant Ka = 1.9 x 10(9) M-1 comparable to that of normal sera (Ka = 1.7-2.1 x 10(9) M-1). The apparent MW of the GHBP was approximately 60-80 kDa, similar to that of control sera. In the proband's sister, parents, grandparents and uncles, extremely high GHBP values were observed (43.0 +/- 4.8 RSB, n = 10) compared with normal adults (0.81 +/- 0.06 RSB) (p << 0.001). The remaining subjects had normal or moderately elevated GHBP levels. Serum GH in adults with high GHBP was significantly elevated above control values (6.0 +/- 0.9 micrograms/l vs 0.76 +/- 0.13 microgram/l, p < 0.001). Serum IGF-I and IGFBP-3 levels were normal in all the subjects, with the exception of an aunt (IGF-I 3.9 nmol/l) and the proband's sister (IGFBP-3 460 micrograms/l). All the subjects' heights were within the normal range. Analysis of the GHR gene performed in the proband revealed an as yet undescribed homozygous intronic point mutation. It consists of a G-->T substitution at nucleotide 785-1 preceding exon 8, a sequence that encodes the transmembrane domain. This mutation, which destroys the invariant dinucleotide of the splice acceptor site, is expected to alter GHR mRNA splicing and to be responsible for skipping exon 8. The resulting truncated protein that retains GH binding activity is probably no longer anchored in the cell membrane, affecting signal transmission in the homozygous patient and causing high GHBP levels in the heterozygous relatives.

GH and GHBP activity and not IGF-1 and its receptor activity express growth velocity reduction during treatment of central precocious puberty by a superactive GNRH analogue

We studied six patients with central precocious puberty (CPP) (five girls and one boy, aged 9-14.4 years) before and after 5 and 12 months of treatment with GnRH-A (D-TRP-6-LHRH-depo, DECAPEPTYL Ferring, Sweden), and 14 age-matched prepubertal children serving as controls. GnRH suppressed gonadal sex hormone secretion and arrested the gonadarche development. Growth velocity decreased from 9.8 +/- 1.6 (mean +/- SD) to 4.6 +/- 1.0 cm/year after 1 year of treatment. Basal serum IGF-1 levels of the CPP patients were 35.4 +/- 2.8 nmol/l, which was significantly higher than that of the controls (18.8 +/- 1.9, P = 0.00007). After GnRH-A there was a slight but significant increase in serum IGF-1 levels from 35.4 +/- 2.8 (mean +/- SE) to 40.3 +/- 2.1 nmol/l after 5 months (mean difference of 4.9 +/- 1.7, P = 0.02), reversing to 35.6 +/- 2.8 nmol/l after 12 months. The number of high affinity IGF-1 binding sites on erythrocytes (RBC) in the controls was 3.3 +/- 0.3 sites/cell, similar to that found in the patients before treatment. Following therapy, the number of the binding sites decreased from 4.0 +/- 0.8 (mean +/- SE) to 2.5 +/- 0.6 sites/cell after 5 months (mean difference of -1.4 +/- 0.5, P = 0.01), to 2.7 +/- 0.7 sites/cell after 12 months. Basal levels of plasma GH in the CPP patients were 7.1 +/- 1.3 ng/ml, significantly higher than those of the controls (1.2 +/- 0.2, P = 0.00001). Treatment decreased plasma GH in patients from 7.1 +/- 1.3 to 1.3 +/- 0.3 ng/ml after 5 months (mean difference of -5.8 +/- 1.3, P = 0.003) and to 2.7 +/- 1.5 ng/ml after 12 months. The GH binding protein (GHBP) activity in the controls was 76.2 +/- 6.2% relative specific binding, similar to that of the patients before therapy. The mean basal GHBP activity of the patients increased from 75.5 +/- 7.3 to 101 +/- 6.4% (mean difference of 25.5 +/- 9.7, P = 0.01) after 5 months and to 90.1 +/- 5.6% after 12 months of treatment. In conclusion, plasma GH and its receptor activity are a better indicator of the GnRH-A effect on growth than IGF-1 and its receptor activity.

Growth hormone (GH) stimulates insulin-like growth factor-I (IGF-I) and IGF-binding protein (IGFBP)-2 gene expression in spleens of juvenile rats

Growth and development of the spleen involves the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. To evaluate the molecular mechanism of these effects we studied the effect of hypophysectomy (Hx) and GH replacement therapy on the expression of IGF-I, the IGF-I receptor and IGF-binding protein-2 (IGFBP-2) in juvenile rats. Hx resulted in a 30% reduction in body weight. GH replacement therapy for seven days partially prevented these effects. IGF-I mRNA levels were reduced 30% by Hx, IGFBP-2 mRNA levels fell 50% whereas IGF-I receptor mRNA levels were unaffected. GH therapy prevented the reduction in IGF-I and IGFBP-2 mRNA levels. These results suggest that the GH effect on splenic growth and development is via local (paracrine) IGF-I expression, in addition to any effect by circulating (endocrine) IGF-I.

Serum growth hormone-binding protein (GHBP) activity is decreased by administration of insulin-like growth factor I in three Laron syndrome siblings with normal GHBP

Three Laron Syndrome (LS) siblings with a post growth hormone (GH) receptor defect for insulin-like growth factor-I (IGF-I) synthesis were found to have serum GH-binding protein (GHBP) levels normal for age. Treatment with recombinant IGF-I (150 micrograms/kg/day) decreased serum GHBP activity to 62% of the basal value (P < 0.001) in two of the sibs in 1 week and in the third sib after 3 months of therapy. Scatchard analysis of the binding of [125I]human GH (hGH) to GHBP in patients' sera before and during therapy revealed affinity constants Ka = 1.55-1.80 x 10(9) M-1, similar to that of sera from healthy subjects. Variations in binding are due to changes in the binding capacity. IGF-I may be a regulatory factor for serum GHBP activity in man.

Laron syndrome due to a post-receptor defect: response to IGF-I treatment

Three siblings with Laron syndrome (LS) and normal serum growth hormone binding protein (GHBP) are described. Basal serum levels of hGH were high and IGF-1 low, and in contradistinction to the classical form of the disease serum GHBP and IGFBP-3 were normal in these patients. After 7 days of human growth hormone administration serum IGFBP-3 levels as well as the number of red blood cell IGF receptor sites increased. After short- and long-term IGF-1 administration the IGF-1 receptor binding capacity as well as the number of IGF receptor sites decreased to levels found in control subjects. One year treatment with IGF-1 increased the growth velocity by 47-96% in the two older children. It is concluded that the findings described are compatible with a normal GH receptor and normal signal transmission for IGFBP-3 synthesis but a defect exists in the post-GH receptor mechanism for the generation of IGF-1. This is the first description of this type of defect leading to a variant of Laron syndrome.

Modulation of IGF-I receptors by exogenous hGH treatment in constitutionally short children

OBJECTIVE

To study the in-vivo regulation of IGF-I binding sites on erythrocytes (RBC) following administration of growth hormone (hGH) to constitutionally short children. Recently, owing to biosynthetic techniques, treatment with hGH has been administered not only to children with GH deficiency but also to children with constitutional growth delay and with familial short stature.

PATIENTS AND DESIGN

Growth hormone (rhGH-Norditropin, Novo/Nordisk) was administered at a dose of 0.1 U/kg/day s.c. to 11 children with constitutional short stature. Before and at 1-2 months after initiation of treatment IGF-I binding sites and serum IGF-I were determined. Erythrocytes were separated from whole blood by centrifugation over Ficoll Hypaque and used to assess IGF-I binding sites.

RESULTS

Serum IGF-I levels increased from 14.93 +/- 1.50 nmol/l (mean +/- SEM) to 30.29 +/- 2.32 nmol/l, with a mean difference of 15.36 +/- 2.21 (P = 0.00001). Concomitantly, the number of binding sites per cell decreased from 5.77 +/- 0.81 sites per cell (m +/- SEM) to 2.10 +/- 0.36, with a mean difference of -3.67 +/- 0.76 (P = 0.0003). The dissociation constant (Kd) also decreased from 0.47 +/- 0.16 nM (m +/- SEM) to 0.10 +/- 0.02 with a mean difference of -0.37 +/- 0.16 (P = 0.02), indicating an increase in the affinity of the receptors.

CONCLUSION

Treatment of children with constitutional short stature with hGH raises the circulating IGF-I levels and down-regulates the IGF-I receptors. This study shows that IGF-I is capable of regulating its homologous receptor concentrations in vivo and it is suggested that the measurement of IGF-I binding sites on RBC may be used for the diagnosis of subtle states of resistance to IGF-I.

Modulation of insulin like growth factor I (IGF-I) binding sites on erythrocytes by IGF-I treatment in patients with Laron syndrome (LS)

The in vivo regulation of IGF-I binding sites was evaluated using erythrocytes (RBC) from 8 patients with Laron syndrome (LS), before and after IGF-I treatment (120-150 micrograms/kg/day s.c.). Basal fasting IGF-I averaged 20.48 +/- 2.06 nmol/l (mean +/- S.E.M.) in the control group as compared to 4.72 +/- 0.84 nmol/l in the 8 LS patients (P = 0.0001). After 1 week of IGF-I treatment serum IGF-I levels increased to 6.53 +/- 1.58 nmol/l (a mean difference of 1.81 +/- 0.95, P = 0.05) and after 1 month of treatment to 14.37 +/- 4.56 nmol/l (a mean difference of 9.37 +/- 4.42, P = 0.03). Concomitantly, we found a significant decrease in the number of high affinity IGF-I binding sites, from 5.74 +/- 0.86 sites/cell (mean +/- S.E.M.) in the non-treated state to 2.29 +/- 0.64 sites/cell and 2.17 +/- 0.53 sites/cell after 1 week and 1 month of treatment, respectively (a mean difference of -3.44 +/- 0.94, P = 0.004 and -3.58 +/- 0.79, P = 0.002, respectively), values similar to those found in the control group. These data demonstrate that replacement treatment of LS patients with IGF-I down regulates its specific receptors. We propose IGF-I binding to RBC as a test to determine the responsiveness of patients considered for long term IGF-I treatment.

Growth hormone (GH) stimulates insulin-like growth factor-I (IGF-I) and IGF-I-binding protein-3, but not GH receptor gene expression in livers of juvenile rats

In the adult rat, expression of the liver GH receptor, insulin-like growth factor-I (IGF-I), and IGF-I-binding protein-3 (IGFBP-3) genes has been shown to be under GH control. Additionally, hypophysectomy and GH treatment have a differential effect on the relative abundance of liver IGF-I mRNA variants in adult rats. To further elucidate the time of appearance and the extent of GH control of liver GH receptor, IGF-I, and IGFBP-3 gene expression, we studied the effect of hypophysectomy and GH and IGF-I treatment in juvenile rats. Male Wistar rats were hypophysectomized (Hx) on postnatal day 26 and received twice daily sc injections of saline, recombinant human GH (2.5 U/kg.day), or recombinant human IGF-I (500 micrograms/kg.day) for 7 days. Sham-operated rats received the same treatment. Hx animals also received T4 (20 micrograms/kg.day). In Hx animals, there was a significant reduction in body weight (69.8 +/- 6.6 vs. 100.4 +/- 5.4 g; P < 0.001). GH, but not IGF-I, treatment increased body weight (79.6 +/- 9.6 g after GH vs. 69.8 +/- 6.6 g before GH; P < 0.05). GH treatment partially maintained liver, kidney, and lung weights in Hx animals and increased them in intact animals, whereas IGF-I treatment did so only in the lungs of intact and Hx animals. Serum GH and IGF-I levels were markedly reduced in Hx animals compared with those in intact controls, and GH treatment maintained, albeit partially, circulating IGF-I levels compared with those in saline-treated Hx animals. IGF-I mRNA levels were markedly reduced in Hx liver (25.0 +/- 5.4%; P < 0.001 compared with intact controls). GH treatment for 7 days increased IGF-I mRNA levels by 4.8-fold over the levels in 9-day Hx animals and increased IGF-I mRNA levels by 2.2-fold in control rats. Hypophysectomy decreased exon 2-containing transcripts by 7.0-fold and exon 1-containing transcripts by 4.1-fold. GH treatment, however, affected both exon 1- and exon 2-containing transcripts similarly. Hepatic IGFBP-3 mRNA levels were reduced in Hx (53.2 +/- 1.8%; P < 0.01 compared with intact controls) and IGF-treated Hx animals, but were not decreased in Hx GH-treated animals (100.6 +/- 9.5). No changes in GH receptor or GH-binding protein mRNA levels were caused by Hx, GH, or IGF-I treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Up-regulation of insulin-like growth factor-I (IGF-I) receptor gene expression in patients with reduced serum IGF-I levels

We have analysed the expression of the IGF-I receptor gene in lymphocytes of patients with low levels of circulating IGF-I (four patients with isolated GH deficiency (IGHD) and one Laron-type dwarf (LTD)) in comparison with a control group exhibiting normal serum IGF-I levels and endocrine profiles. 125I-Labelled IGF-I binding assays were performed on erythrocytes to determine the number of IGF-I binding sites per cell and their dissociation constants. Erythrocytes from patients with IGHD or LTD contained significantly (P = 0.002) more receptors per cell (10.9 +/- 3.1 binding sites/cell), with a reduced affinity (Kd = 0.49 +/- 0.05 nM), than erythrocytes from controls (2.0 +/- 0.4 sites/cell; Kd = 0.14 nM). The levels of IGF-I receptor mRNA in circulating lymphocytes were determined by an RNA template-specific reverse transcription/polymerase chain reaction method. There was a statistically significant increase in IGF-I receptor mRNA levels in lymphocytes from patients with LTD or IGHD when compared with controls (3108.1 +/- 775.9 vs 576.0 +/- 465.7 arbitrary units, P = 0.006). The increased level of IGF-I binding due to increased IGF-I receptor gene expression may represent a compensatory up-regulation process activated in response to the low levels of IGF-I in the circulation of patients with LTD or IGHD.

The early postnatal development of the murine mandibular condyle is regulated by endogenous insulin-like growth factor-I

Skeletal growth during the early postnatal period is thought to be GH-independent, and is probably regulated by intrinsic growth factors. We studied the involvement of locally produced insulin like growth factor-I (IGF-I) in the growth of the neonatal mandibular condyle. Immunofluorescence studies revealed intense staining with antibodies to IGF-I in the mandibular condyle of 2-day-old ICR mice. We have also shown that these mandibular condyles contain specific high-affinity binding sites (Kd = 0.157 nmol/l) for IGF-I (427 fmol/mg). Autoradiographical studies of iodinated IGF-I revealed that the distribution of the receptors for IGF-I was parallel to that of IGF-I production, mainly in the younger zones of the condyle, namely the chondroprogenitor and the chondroblast cell layers. Immunoinhibition of IGF-I resulted in an almost complete inhibition (-91%) of thymidine incorporation into DNA, as well as in marked degenerative changes in the morphological appearance of the condyle. Our studies support the hypothesis that early postnatal growth is dependent on the paracrine activity of endogenous GH-independent IGF-I.

Erythrocytes from patients with low serum concentrations of IGF-I have an increase in receptor sites for IGF-I

The binding characteristics of insulin-like growth factor I on erythrocytes were studied in 11 patients with long-term IGF-I deprivation and low serum IGF-I levels. Six patients had Laron type dwarfism and 5 idiopathic isolated growth hormone deficiency, with a mean (+/- SEM) serum IGF-I level of 6.01 +/- 1.01 nmol/l as compared with that in 25 normal controls of 26.35 +/- 2.73 nmol/l (p = 0.00001). The mean (+/- SEM) [125I]IGF-I specific binding at a concentration of 4 x 10(12) cell/l was 12.11 +/- 1.29% for the patient group compared with 8.75 +/- 0.62% for the controls (p = 0.005). Scatchard analysis showed a curvilinear plot. Using a non-linear curve fit, the mean (+/- SEM) number of high-affinity receptor sites per cell was found to be 7.34 +/- 1.80 in the IGF-I-deprived patients and 2.84 +/- 0.29 in the controls (p = 0.0005). The mean +/- SEM dissociation constant was found to be 0.33 +/- 0.10 nmol/l for the patients and 0.26 +/- 0.08 nmol/l for the controls (NS). This study has demonstrated that the low serum concentration of IGF-I in Laron type dwarfism and isolated growth hormone deficiency is associated with an increase in receptor sites for IGF-I on the erythrocytes. The application of this property as a diagnostic acid remains to be established.

Some properties of the plasma hGH activity in patients with Laron-type dwarfism determined by a radioreceptor assay using human liver tissue

A radioreceptor assay for human growth hormone (hGH) using the 100,000-g pellet of human liver tissue homogenates obtained from a 13-year-old male donor of a kidney transplantation is described. The dilution curves of the plasma hGH of 6 patients with Laron-type dwarfism (LTD) as well as those of the plasma hGH from 1 normal child and 2 acromegalic patients were all found to be parallel to the standard curve, suggesting that in the LTD syndrome the circulating hGH is biologically active.

Direct visualization of binding, aggregation and internalization of human growth hormone in cultured human lymphocytes

The distribution of human growth hormone (hGH) receptor complexes on IM-9 cultured lymphocytes was studied using fluorescein and 125I-labelled hGH (F-hGH and [125I]hGH). The cells labelled with F-hGH were visualized with a sensitive video intensification microscopic system which permitted direct observation of the location of the fluorescent hormone on the surface of the living lymphocytes. At 4 degrees C F-hGH bound diffusely to the cell surface and remained dispersed but following incubation for 30 min at 37 degrees C the hormone receptor complexes aggregated into patches on the cell surface and formed a single cap on one pole of the cell. Progressive internalization into the cell was demonstrated at 37 degrees C with [125I]hGH. It is hypothesized that the aggregation and internalization of the hGH receptor complexes are associated with the action and degradation of the hormone and probably also with the mechanism of down-regulation of the receptors.

Defect of human growth hormone receptors in the liver of two patients with Laron-type dwarfism

Liver microsome pellets prepared from tissue obtained by elective open biopsy from two patients (aged 4 and 26 years) with Laron-type dwarfism (LTD) showed no specific binding of 125I-hGH (human growth hormone). In contrast, 31 assays of liver microsomes obtained immediately after clinical death from 6 healthy subjects (kidney transplantation donors with a mean age of 24 years) showed a mean specific binding of 14% (range 7.9 to 24%). We interpreted these findings as evidence that in patients with LTD there is a defect in the hGH receptors of the liver and a consequent lack of somatomedin generation. The fact that the liver microsomes from the two LTD patients showed active specific binding of 125I-insulin suggest that, in this syndrome, it is only the receptors for hGH that are defective.

Growth hormone resistance

Biological ineffectiveness of endogenous or exogenous growth hormone (GH) (i.e. a state or resistance) has been reported in several clinical conditions. The most typical form is Laron-type dwarfism, a hereditary disease which is clinically undistinguishable from isolated GH deficiency and which is characterized by high levels of plasma hGH but low somatomedin (SM). It is shown that the GH molecule binds normally to human liver receptors proving its normalcy. Thus the disease is due to an inability to generate active SM. States of resistance to exogenous GH by receptor occupancy exist when endogenous hormone is secreted in large amounts (newborns, acromegaly) or even normal amounts. Endorgan resistance to SM and GH such as in Pygmies represent an additional type. GH resistance is also induced by a rise in antibodies to GH by use of an impure or altered preparation or in a rare form of lack of immunotolerance to hGH, or by an enhancement of SM inhibitors as is seen in chronic renal failure or corticosteroid overdosage.

Heterogeneity of pituitary and endogenous plasma human growth hormone from fetuses, premature and full-term newborns

Fetal and adult human growth hormone (HGH) extract from human pituitaries as well as plasma from premature and full-term newborns and children were submitted to chromatography on Sephadex G-75 and the immunoreactive HGH (IRHGH) in the elution fractions was determined quantitatively by radioimmunoassay. Three fractions of IRHGH could be differentiated according to the elution pattern: 'big-big', 'big' and 'little' IRHGH. In fetal pituitary extract only 'big-big' and 'little' IRHGH were found, whereas in adult pituitary extract all three forms of IRHGH were present. In the plasma samples studied no 'big-big' form was found; only 'big' and 'little' IRHGH appeared. In addition, plasma samples of premature newborns had a smaller proportion of the 'big' IRHGH than did those of the full-term newborns and older children.