Insulin-infusion-pump treatment of diabetes: influence of improved metabolic control on plasma somatomedin levels

Serum IGF-1 to IGFBP-3 Molar Ratio: A Promising Diagnostic Tool for Growth Hormone Deficiency in Children

BACKGROUND

The serum insulin-like growth factor-1 (IGF-1)/insulin-like growth factor binding protein-3 (IGFBP-3) ratio has various potential applications in growth hormone-related disorders. This study aimed to investigate the performance of the IGF-1/IGFBP-3 ratio, independently and in combination with serum IGF-1 and IGFBP-3, in the diagnosis of growth hormone deficiency (GHD) in children with short stature (SS).

METHODS

A 7-year cross-sectional observational study was conducted on 235 children with SS. Participants with known disorders that may affect IGF-1 other than GHD were excluded. Participants were classified into GHD (n = 64) and non-GHD (n = 171) groups. GHD was defined as a slow growth rate (<25th percentile over 1 year) and suboptimal growth hormone (GH) response to 2 GH stimulation tests (peak GH < 6.25 ng/mL using the DiaSorin Liaison assay). The sensitivity and specificity of serum IGF-1, IGFBP-3, and IGF-1/IGFBP-3 molar ratio, independently and in various combinations, were determined.

RESULTS

GHD was diagnosed in 27.2% of participants. Among all studied variables, a low serum IGF-1/IGFBP-3 ratio demonstrated the greatest sensitivity for GHD (87.5%), with a comparable specificity (83.0%). The combination of low serum IGF-1, IGFBP-3, and IGF-1/IGFBP-3 ratio demonstrated the greatest specificity for GHD (97.7%), whereas the combination of normal serum IGF-1, IGFBP-3, and IGF-1/IGFBP-3 ratio demonstrated the greatest specificity for a non-GHD cause of SS (100.0%).

CONCLUSION

Our data suggest that the serum IGF-1/IGFBP-3 ratio is a useful marker for the diagnosis of GHD in children who do not have other disorders that may affect serum IGF-1 levels. Further large studies are needed to confirm the diagnostic utility of the serum IGF-1/IGFBP-3 ratio.

Use of the Growth Hormone Stimulation Test Result in the Management of Patients With a Short Stature

Introduction A proportionate short stature (SS) assessment involves the documentation of normal growth hormone secretion via a growth hormone (GH) stimulation test. All available GH stimulation tests have some disadvantages. The decision to initiate GH therapy is dependent on multiple factors, including the GH stimulation test result. However, many patients receive GH therapy, even if they have a normal GH stimulation test result, with the indication of a presumed idiopathic SS. Objective In this study, we investigated the use of the GH stimulation test result in initiating GH therapy. Method A cross-sectional study was conducted with patients diagnosed with proportionate SS. Age, gender, insulin-like growth factor 1 (IGF-1) level, and GH stimulation test results were collected retrospectively from the electronic medical records. The main outcome variable was the decision related to prescribing GH therapy. Results A total of 286 patient charts were reviewed, and the majority (n = 201, 64.6%) were male. For just less than half (n = 136, 47.6%), the result of the GH stimulation test was ≥ 10 ng/mL, in a small proportion (n = 53, 18.5%) the result was < 5 ng/mL, and for the rest of the cohort, the result was 5.0 - 9.9 ng/mL. The majority (n = 219, 70.4%) received GH therapy, irrespective of the GH stimulation test result. The odds ratio (OR) for GH treatment was 3.9 (CI: 1.79 - 8.49) and 3.0 (CI: 1.21 - 7.42) for patients with a result < 5 ng/mL and 5.0 - 9.9 ng/mL, respectively, compared to the group with a result of ≥ 10 ng/mL. Conclusion GH therapy is frequently prescribed for patients with SS, irrespective of the GH stimulation test result. However, the group with SS with a result of < 9.9 ng/mL was more likely to receive GH therapy. The question of whether a GH stimulation test is required, in the context of SS, is debatable.

Biomarkers of GH action in children and adults

Growth hormone (GH) and IGF-I levels in serum are used as biomarkers in the diagnosis and management of GH-related disorders but have not been subject to structured validation. Auxological parameters in children and changes in body composition in adults, as well as metabolic parameters and patient related outcomes are used as clinical and surrogate endpoints. New treatment options, such as long acting GH and GH antagonists, require reevaluation of the currently used biochemical biomarkers. This article will review biomarkers, surrogate endpoints and clinical endpoints related to GH treatment in children and adults as well as in acromegaly.

Impact of insulin resistance on insulin-like growth factor-1/insulin like growth factor-binding protein-3 axis and on early weight gain in small for gestational age infants

OBJECTIVE

To assess insulin-like growth factor-1 (IGF-1)/IGF-binding protein-3 (IGFBP-3) axis and insulin resistance (IR) and the relationship of these parameters with growth in appropriate for gestational age (AGA) and small for gestational age (SGA) infants at birth and in early infancy.

METHODS

Postnatal blood samples for measurement of glucose, insulin, IGF-1, and IGFBP-3 were taken from 60 infants (30 AGA and 30 SGA) at birth and at one, three, and six months of age. Both SGA and AGA infants were divided into two groups: growing well and not growing well. Blood glucose, insulin, IGF-1, and IGFBP-3 values were assessed in all infants.

RESULTS

Homeostasis model assessment-IR (HOMA-IR) values in well-growing SGA infants in the third and sixth months were found to be higher than in not well-growing SGA infants (3.9±0.8 vs. 1.0±0.3 at 3 months and 3.3±0.9 vs. 2.4±0.9 at 6 months, p<0.05). IGF-1 levels in well-growing SGA infants at 3 and 6 months were found to be higher than those in not well-growing SGA infants (83.80±44.50 vs. 73.50±17.60 ng/mL at 3 months and 95.12±50.74 vs. 87.67±22.91 ng/mL at 6 months, p<0.05). The IGF-1 values were significantly lower in well-growing SGA infants than in well-growing AGA infants (83.80±44.50 vs. 103.31±30.81 ng/mL at 3 months and 95.12±50.74 vs. 110.87±26.44 ng/mL at 6 months, p<0.05).

CONCLUSIONS

This study demonstrates the effects of accelerated early infant growth on IGF-1/IGFBP-3 axis in SGA-born infants.

Parathormone--25(OH)-vitamin D axis and bone status in children and adolescents with type 1 diabetes mellitus

BACKGROUND

Skeletal involvement in patients with type 1 diabetes mellitus (T1DM) has complex pathogenesis and despite numerous researches on this problem, many questions remain unanswered.

OBJECTIVE

This study aimed to assess bone status by measurement parathormone (PTH), 25-hydroxy vitamin D [25(OH)D] serum levels in children and adolescents with T1DM and its relation to insulin-like growth factor-1 (IGF-1), disease duration, puberty stage, and metabolic control.

PATIENTS AND METHODS

This study included 36 children and adolescents with T1DM and 15 apparently healthy controls. Serum levels of 25(OH)D, PTH, IGF-1 measured using enzyme-linked immunosorbent assay (ELISA), while glycosylated hemoglobin (HbA1c), calcium (Ca), inorganic phosphorus (PO(4) ) using autoanalyzer. Bone quality assessed using dual energy X-ray absorptiometry (DEXA).

RESULTS

Diabetic patients showed significant increase in PO(4) and PTH levels, while significant decrease in Ca, IGF-1, and 25(OH)D serum levels. As much as 52.8% of patients showed reduced 25(OH)D, and 30.65% showed elevated PTH serum levels. In diabetic patients, abnormal bone status (osteopenia-osteoporosis) found mostly in total body (94.40%) then lumber-spine (88.90%), ribs (88.90%), pelvis (86.10%), thoracic-spine (80.60%), arms (80.60%) and legs (77.80%), while head bones showed no abnormalities. Long diabetic duration had negative; meanwhile PTH, onset age, and puberty age had positive impact on bone status.

CONCLUSIONS

Children and adolescent with T1DM have abnormal bone status mostly in axial skeleton which may be contributed to impairment of formation of 25(OH)D and IGF-1. Physical activity, calcium and vitamin D supplement seem important in T1DM. Elevated serum PTH level in diabetic patients is not uncommon and its positive correlation with bone status needs further investigations.

The glomerular podocyte as a target of growth hormone action: implications for the pathogenesis of diabetic nephropathy

Involvement of the growth hormone (GH) / insulin-like growth factor 1 (IGF-I) axis in the pathogenesis of diabetic nephropathy (DN) is strongly suggested by studies investigating the impact of GH excess and deficiency on renal structure and function. GH excess in both the human (acromegaly) and in transgenic animal models is characterized by significant structural and functional changes in the kidney. In the human a direct relationship has been noted between the activity of the GH/IGF-1 axis and renal hypertrophy, microalbuminuria, and glomerulosclerosis. Conversely, states of GH deficiency or deficiency or inhibition of GH receptor (GHR) activity confer a protective effect against DN. The glomerular podocyte plays a central and critical role in the structural and functional integrity of the glomerular filtration barrier and maintenance of normal renal function. Recent studies have revealed that the glomerular podocyte is a target of GH action and that GH's actions on the podocyte could be detrimental to the structure and function of the podocyte. These results provide a novel mechanism for GH's role in the pathogenesis of DN and offer the possibility of targeting the GH/IGF-1 axis for the prevention and treatment of DN.

Are IGF-I and IGF-BP3 useful for diagnosing growth hormone deficiency in children of short stature?

BACKGROUND

The diagnosis of growth hormone deficiency (GHD) is based on clinical and auxological characteristics combined with the results of growth hormone provocation tests.

AIM

To evaluate the utility of IGF-I and IGF-BP3 serum levels in the diagnosis of GHD among children of short stature.

SUBJECTS/METHODS

We recruited 207 short pre-pubertal children and divided them into two groups. One group consisted of 70 children (mean age 7.93 +/- 2.35 SD) with a growth hormone (GH) response on two provocative tests of < or = 8 ng/ml, while the other group contained 137 children (mean age 7.92 +/- 2.11 SD) with a peak GH value of > 8 ng/ml. Serum IGF-1 and IGF-BP3 levels were determined in the two groups.

RESULTS

The difference in serum IGF-I between the two groups was not significant (p= 0.26), while the difference in IGF-BP3 between the two groups was statistically significant (p= 0.004). The performance of serum IGF-1 and IGF-BP3 as a diagnostic tool, expressed as AUC by ROC analyses, was quite low.

CONCLUSION

Neither IGF-I nor IGF-BP3 are an adequate substitute for the stimulus test in the diagnosis of growth hormone deficiency among children of short stature.

Continuous subcutaneous insulin infusion (CSII) versus multiple insulin injections for type 1 diabetes mellitus

BACKGROUND

Type 1 diabetes is a metabolic disorder resulting from a defect in insulin secretion. Onset of type 1 diabetes mellitus may occur at any age and it is one of the most common chronic diseases of childhood and adolescence. Since there are no interventions known to prevent onset, it is vital that effective treatment regimes are available. Glycaemic control is maintained by replacement of insulin and may be in the form of 'conventional' insulin therapy (multiple injections per day) or continuous subcutaneous insulin infusion (CSII).

OBJECTIVES

To assess the effects of CSII compared to multiple insulin injections (MI) in people with type 1 diabetes mellitus.

SEARCH STRATEGY

Studies were obtained from electronic searches of The Cochrane Library, MEDLINE, EMBASE and CINAHL.

SELECTION CRITERIA

Studies were included if they were randomised controlled trials comparing CSII with three or more insulin injections per day (MI) in people with type 1 diabetes mellitus.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed risk of bias and extracted characteristics of included studies. Authors contacted study investigators to obtain missing information. Generic inverse variance meta-analyses using a random-effects model were performed.

MAIN RESULTS

Twenty three studies randomised 976 participants with type 1 diabetes to either intervention. There was a statistically significant difference in glycosylated haemoglobin A1c (HbA1c) favouring CSII (weighted mean difference -0.3% (95% confidence interval -0.1 to -0.4). There were no obvious differences between the interventions for non-severe hypoglycaemia, but severe hypoglycaemia appeared to be reduced in those using CSII. Quality of life measures suggest that CSII is preferred over MI. No significant difference was found for weight. Adverse events were not well reported, no information is available on mortality, morbidity and costs.

AUTHORS' CONCLUSIONS

There is some evidence to suggest that CSII may be better than MI for glycaemic control in people with type 1 diabetes. Non-severe hypoglycaemic events do not appear to be reduced with CSII. There is insufficient evidence regarding adverse events, mortality, morbidity and costs.

Acute phase modulation of systemic insulin-like growth factor-1 and its binding proteins after major burn injuries

OBJECTIVES

To provide a detailed, sequential analysis of insulin-like growth factor-1 and its binding proteins in adults during the acute phase after a major burn injury.

DESIGN

Descriptive, repeated measurements for quantitation and characterization of insulin-like growth factor-1 and its binding proteins in adult burn survivors.

SETTING

Burn center in a university hospital.

PATIENTS

A total of 17 severely burned (>15% total body-surface area burned) adult patients.

INTERVENTIONS

Venous blood was collected twice a day for 10 days and centrifuged, and the sera were stored at -80 degrees C until analysis. A series of 340 serum samples were analyzed by radioimmunoassay to determine the circulating concentration of insulin-like growth factor-1 and its major binding proteins (insulin-like growth factor-binding protein), by Western ligand blotting. To better understand the changes seen in systemic insulin-like growth factor-binding protein-3 levels by Western ligand blotting, a proteolysis assay was performed.

MEASUREMENTS AND MAIN RESULTS

Insulin-like growth factor-1 levels were reduced from day 0 and correlated with insulin-like growth factor-binding protein-1 and -2 (p <.01), but not insulin-like growth factor-binding protein-3 and -4. Insulin-like growth factor-binding protein-3 was decreased relative to normal on day 0, declined further until day 3, and began recovering by day 6, but returned to only 35% of normal by day 10. Insulin-like growth factor-binding protein-1 and -2 were increased relative to normal and remained increased throughout the 10-day period. Insulin-like growth factor-binding protein-4 concentrations, however, were similar to normal at day 1 but gradually increased over time. Burn serum incubated with recombinant human glycosylated iodine-125 insulin-like growth factor-binding protein-3 did not demonstrate any proteolysis, although proteolysis of nonglycosylated iodine-125 insulin-like growth factor-binding protein-3 reached levels of approximately 40%.

CONCLUSIONS

Insulin-like growth factor-binding protein-3 proteolysis does not seem to be the mechanism by which systemic insulin-like growth factor-1 levels are reduced in major burn survivors. In vitro proteolysis of recombinant human glycosylated and nonglycosylated iodine-125 insulin-like growth factor-binding protein-3 does not reflect the in vivo situation in major burn survivors.

Evaluation of total IGF-I assay methods using samples from Type I and Type II diabetic patients

Measurements of circulating insulin-like growth factor-I (IGF-I) levels are an important part of many studies on growth and development. Circulating IGF-I levels are growth hormone (GH) dependent and are also impacted by age, gender, nutritional status and disease. Moreover, IGF-I is the main pharmacodynamic marker of GH activity. The majority of circulating IGF-I is associated with high affinity insulin-like growth factor-binding proteins (IGFBPs), making accurate and precise measurements of total IGF-I concentrations in biological matrices technically challenging. Many total IGF-I assay methods combine an immunoassay with a sample preparation method aimed at removing IGFBPs. However, not all sample preparation methods efficiently remove all IGFBPs or BP fragments (BPFs), and there is currently no reference method for IGF-I measurement against which these IGF-I assays can be calibrated. We have evaluated a number of IGF-I immunoassays and sample preparation methods using plasma samples from normal donors and from donors with Type I and Type II diabetes mellitus. In order to eliminate the variability between assays due to differences in assay standardization, we used the same preparation of highly pure, fully characterized IGF-I as the standard for all assays. We found that the data produced by many of the IGF-I assay methods showed good agreement when IGF-I levels in samples from normal individuals were measured. However, we found that these agreements were quite poor when IGF-I levels in samples from diabetics were measured. This was true of methods that claimed to physically separate IGFBPs from IGF-I either by acid/ethanol extraction or by acid chromatography. Several methods have recently been developed that physically separate IGF-I from IGFBPs followed by a chemical displacer to displace any residual BPs or BPFs from IGF-I. We found that the data generated by these displacement methods showed good agreement when assaying samples from diabetic as well as normal donors. There is considerable discussion in the literature as to whether individuals with diabetes have normal circulating levels of IGF-I. Many of the published studies are based on assays that may not accurately measure IGF-I levels due to problems with assay standardization and/or with assay methodology. Displacement methods may enable us to more accurately measure IGF-I levels in diabetes.

Is there a medical need to explore the clinical use of insulin-like growth factor I?

Cloning of the insulin-like growth factor I (IGF-I) gene led to the development in 1987 of recombinant IGF-I available for clinical use. Trials were started targeting endocrine, metabolic and neurological disorders, and beneficial results have been demonstrated in IGF-I deficiency states caused by IGF-I gene deletion and growth hormone (GH) receptor deficiency, type 1 and type 2 diabetes mellitus, and severe insulin resistance syndromes. Results of equivocal benefit have also been reported in osteoporosis and amyotrophic lateral sclerosis. Recent encouraging data using the IGF-I-IGF-binding protein 3 (IGFBP-3) complex in diabetes mellitus suggest that this preparation may eventually replace recombinant free IGF-I. The lack of an established therapeutic indication for IGF-I has resulted in its supplies being severely limited. It will probably be decided during the next decade whether use of IGF-I or the IGF-I-IGFBP-3 complex becomes firmly established as an accepted endocrine therapy.

Continuous subcutaneous insulin infusion therapy for children and adolescents: an option for routine diabetes care

OBJECTIVE

The purpose of this study was to determine the feasibility of continuous subcutaneous insulin infusion (CSII) (insulin pump) therapy in routine pediatric diabetes care by comparing the HbA(1c), body mass index (BMI), and hypoglycemic episodes before and after initiation of CSII therapy.

RESEARCH DESIGN AND METHODS

Data from 56 patients (7-23 years old) were collected during regularly scheduled visits at a frequency similar to non-CSII patients.

RESULTS

The data were analyzed for the entire cohort and 3 subgroups (decreased, stable, or increased HbA(1c)) stratified according to a >/=0.5% change in HbA(1c). The total cohort demonstrated a decrease in HbA(1c) from 8.5% to 8.3%. The decreased cohort (39.4% of the total cohort) demonstrated a significant decrease in HbA(1c) from 8.6% to 7.6%. The mean HbA(1c) of the stable cohort (41.0%) was 8.7%. The increased cohort (19.6%) had an increase in HbA(1c) from 7.8% to 8.8%. Thirty-six patients (64.3%) maintained or achieved a HbA(1c) <8.0% or achieved a HbA(1c) at least 1% lower than their pre-CSII level. Of concern, 6 patients (10.7%) demonstrated a clinically significant increase in HbA(1c) from 8.3% to 9.6%. For the entire cohort, the rate of severe hypoglycemia before and on CSII therapy was 12.3 and 9.5 events per 100 patient-years, respectively. A statistically significant proportion of patients reported a decrease in seizure frequency versus an increase (17.9% vs 1.8%) as well as a decrease in overall hypoglycemic frequency versus an increase (41.1% vs 17.9%). There was not a clinically significant increase in BMI, even in the decreased HbA(1c) cohort.

CONCLUSIONS

CSII therapy is an appropriate option for some children in routine pediatric diabetes care. It can effectively decrease the HbA(1c) and reduce hypoglycemic episodes, without producing an abnormal increase in BMI.

Insulin regulation of human hepatic growth hormone receptors: divergent effects on biosynthesis and surface translocation

Insulin modulates the biological actions of GH, but little is known about its effect on human hepatic GH receptors (GHRs). Using the human hepatoma cell line HuH7 as a model, we investigated insulin regulation of total, intracellular, and cell surface GHRs and receptor biosynthesis and turnover. Insulin up-regulated total and intracellular GHRs in a concentration-dependent manner. It increased surface GHRs in a biphasic manner, with a peak response at 10 nmol/L, and modulated GH-induced Janus kinase-2 phosphorylation in parallel with expression of surface GHRs. The abundance of GHR messenger ribonucleic acid and protein, as assessed by RT-PCR and Western analysis, respectively, markedly increased with insulin treatment. To examine whether insulin regulates GHRs at the posttranslational level, its effects on receptor surface translocation and internalization were investigated. Insulin suppressed surface translocation in a concentration-dependent manner, whereas internalization was unaffected. Moreover, insulin actions on total GHRs and surface translocation were inhibited by PD98059 and wortmannin, respectively. In conclusion, insulin regulates hepatic GHR biosynthesis and surface translocation in a reciprocal manner, with surface receptor availability the net result of the divergent effects. The divergent actions of insulin appear to be mediated by the mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways, respectively.

Insulin-like growth factor binding proteins (IGFBPs) in serum and urine and IGFBP-2 protease activity in patients with insulin-dependent diabetes mellitus

Diabetes mellitus and glucose dysregulation have significant effects on the circulating level of insulin-like growth factor-I (IGF-I) and IGF binding proteins (IGFBPs). In the present study, serum and urine IGFBP (IGFBP-1, -2, and -3) and serum IGF-I and -II levels were measured by radioimmunoassay (RIA) in 27 patients with type 1 diabetes aged 9 to 48 years compared with 9 healthy subjects aged 10 to 28 years. The patients were divided into 3 groups according to the amount of albumin excreted in 24 hours. The macroalbuminuria group (>500 mg/24 h) had elevated serum IGFBP-1 and -2 and decreased IGF-I levels (P < .01 v normal controls). Serum IGFBP-3 and IGF-II were not different among the patient groups and controls (P > .05). The mean urinary IGFBP-1 was decreased in all 3 patient groups compared with the controls (P < .05). Urinary IGFBP-2 and IGFBP-3 were increased in patients with macroalbuminuria. Immunoblot analysis showed increased low-molecular-weight fragments of urinary IGFBP-2 in the poorly controlled diabetics, and direct evidence for increased urinary IGFBP-2 proteolytic activity could be demonstrated in both the microalbuminuric and macroalbuminuric groups. Low-molecular-weight fragments of urinary IGFBP-3 were also increased in both the microalbuminuric and macroalbuminuric groups. In conclusion, alterations of IGFBPs in urine and serum are related to metabolic control in diabetic patients, and there is an increase of urinary IGFBP-2 protease activity in poorly controlled diabetics. The changes in serum IGFBP concentrations (eg, increases in IGFBP-1 and IGFBP-2) may lead to alterations in the availability of IGF-I to peripheral tissues.

Advanced glycosylation end products (AGEs), insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 (IGFBP-3) in patients with type 2 diabetes mellitus

BACKGROUND

Advanced glycosylation end product (AGE) formation is a major mechanism for the development of complications in diabetes, and the possible roles of insulin-like growth factor 1 (IGF-1) and IGF binding protein 3 (IGFBP-3) are not clearly established.

METHODS

We examined the associations of AGEs, free IGF-I and IGFBP-3 in Type 2 diabetes mellitus (DM) patients under diverse conditions. In a cross-sectional design we studied 110 subjects (67 women and 43 men): non-diabetic controls in group 1, (n = 15) and diabetes patients as follows: group 2, without complications (n = 25); group 3, with chronic complications (n = 25); group 4, with acute or chronic infections (n = 24); group 5, hospitalized for reasons unrelated to diabetes (n = 9); group 6, with end-stage renal disease (ESRD) (n = 12). AGEs were determined by a spectrofluorometric method (HPLC). Insulin and IGFBP-3 were measured by RIA and free IGF-1 with an IRMA method.

RESULTS

AGEs were 13-fold higher in patients with ESRD (p<0.001), and lower in healthy individuals. Free IGF-1 was lower in the patients with complications (p = 0.017), with infections (p = 0.006) and hospitalized (p = 0.04). IGFBP-3 was higher in hospitalized patients (p=0.017). AGEs were associated with free IGF-1 (r = 0.41, p = 0.04) in the group with complications, and with HbA(1c) (r = -0.90, p = 0.002) in hospitalized patients. In the total group, free IGF-1 (r = -0.25, p = 0.008), and IGFBP-3 (r = -0.22, p = 0.021) were associated with HbA(1c).

CONCLUSION

We concluded that AGEs were markedly increased in diabetic patients with ESRD, IGF-1 was decreased in patients with infections and hospitalized, and was negatively associated with HbA(1c). IGFBP-3 was increased in hospitalized patients, with higher levels in patients with long bone fractures. A complex interaction of humoral factors may participate in the acceleration of complications of diabetes.

Regulation of growth hormone receptor gene expression

Pituitary growth hormone (GH) is essential for postnatal growth in animals. GH exerts its actions by direct effect on target organs and by stimulating the production of insulin-like growth factor I (IGF-I). At the tissue level, the pleiotropic actions of GH result from the interaction of GH with a specific cell surface receptor, the GH receptor (GHR). The GHR belongs to the hematopoietic receptor superfamily. The human GHR is the product of a single gene located on chromosome 5p13.1-p12 and spans at least 87 kb. Transcripts from this gene are characterized by the presence of disparate 5' untranslated exons. In the liver at least eight different GHR 5' untranslated regions (UTRs) have been described. This heterogeneity in the 5' UTR most likely results from the splicing of the various exon 1 fragments to a common splice site located 11 bp upstream of the initiating ATG. Heterogeneity in the 5' UTR sequences of the GHR transcripts indicates that transcriptional control of the locus is complex. GHR gene expression is minimal to absent in the fetus, with the postnatal increase in expression in the liver being maximal during pregnancy. GHR gene expression is also regulated by factors such as nutritional intake, GH, steroid hormones, and diabetes mellitus. Available information about the molecular mechanisms regulating expression of the GHR gene is discussed. Thus the GHR gene presents a picture of multiple 5' untranslated exons under the control of multiple promoters. The use of alternate promoters for initiation of transcription in conjunction with differential splicing allows for exquisite regulation of gene expression. This schema is appropriate for a protein that is essential to many of the physiological processes that are crucial for the survival and well-being of the organism.

Effects of octreotide on glycaemic control, glucose disposal, hepatic glucose production and counterregulatory hormones secretion in type 1 and type 2 insulin treated diabetic patients

We studied the effects of continuous subcutaneous infusion of octreotide (100 micrograms/day for 5 days) on glycaemic values, counterregulatory hormones secretion, hepatic glucose production (HGP) and glucose disposal during an euglycaemic clamp in 7 C-peptide-negative type 1 diabetic patients and 7 C-peptide positive insulin-treated type 2 diabetic patients. In type 1, but not type 2 diabetic patients, octreotide significantly reduced glycaemic values (P < 0.005) and also diminished HGP during an euglycaemic clamp (P < 0.05). However, insulin stimulated global glucose uptake remained unchanged. GH, glucagon, IGF-I, IGFBP-3 levels, were significantly lowered by octreotide in both type 1 and type 2 diabetic patients whereas cortisol and epinephrine remained unmodified. Moreover in type 2 diabetic patients both basal (P < 0.05) and after-meal (P < 0.01) C-peptide secretion was reduced by octreotide. These data point to different metabolic effects of octreotide in type 1 versus type 2 diabetic patients with the drug only being able to reduce glycaemic values and HGP in the former but not in the latter subjects. The failure of octreotide to diminish glycaemic values and HGP in type 2 diabetic patients in spite of its ability to lower GH and glucagon may probably depend on temporary blockage of residual endogenous insulin secretion induced by octreotide administration.

Vascular reactivity and platelet aggregability during the first five years of insulin-dependent diabetes in children

Skin microvascular reactivity and platelet aggregation in response to collagen and adenosine diphosphate (ADP) was studied prospectively in a population-based cohort of children with newly acquired type 1 diabetes mellitus (IDDM), who have now been followed up longitudinally for 5 years. The skin microvascular vasodilation in response to ischaemia was recorded by means of transcutaneous oximetry at 37 degrees C and compared with that in a control group of 58 healthy children. Platelet aggregation was compared with 42 healthy control children. Sixty months after diagnosis, the same degree of impairment of vasodilatory capacity was noted as previously recorded at 24 months and on admission, on all these occasions being significantly lower than the control value and the results from the 12-month follow-up. A sex difference was noted, diabetic girls both during and after puberty exhibiting a greater impairment of vasodilator capacity as compared with diabetic boys. The same degree of platelet aggregation in response to collagen was noted 60 months after diagnosis as had been recorded previously at 24 and 12 months, all significantly increased as compared with the results from admission, but not different from those in controls. By contrast, the aggregation in response to ADP was now lower than that observed on admission. No statistically significant gender difference was noted. The implication of the impaired skin microvascular vasodilation and of the changing pattern of platelet aggregation for later diabetic angiopathy needs to be evaluated in the coming decade.

[Growth of children with insulin-dependent diabetes. Study of 104 cases]

BACKGROUND

Results of studies of growth in children with diabetes mellitus are still conflicting. In a cross-sectional and longitudinal study, statural growth was analysed in a sample of diabetic children in order to specify its characteristics and relationship with various factors.

POPULATION AND METHODS

One hundred and four children (53 girls and 51 boys) with insulin-dependent diabetes for more than 3 years have been studied (age at onset and duration of diabetes, respectively, 6.4 +/- 4.1 and 8.5 +/- 4.8 in girls; 6.1 +/- 3.9 and 7.9 +/- 3.9 in boys; m +/- SD). A control group included 51 boys (age: 8.9 +/- 2.9) and 49 girls (age: 9.3 +/- 2.7). Data were collected every three months. Hemoglobin A1c was measured using high performance liquid chromatography (normal range: 5.0 +/- 1.0%; m +/- 2 DS).

RESULTS

At diagnosis, height (evaluated in SD) did not differ between diabetic children and controls. Three years before the onset of diabetes, boys were taller compared to controls (1.02 +/- 0.20 vs 0.41 +/- 0.17; P < 0.05; m +/- SEM). Children five years after the onset of disease were overweight compared to controls (girls: 0.96 +/- 0.16 vs 0.00 +/- 0.20; boys: 0.59 +/- 0.16 vs -0.04 +/- 0.15; P < 0.01; m +/- SEM). Longitudinal study showed a progressive decrease of mean growth velocity starting at least 2 years before the onset of diabetes and proceeding until the end of growth. From diagnosis to the end of height development, there was a growth loss of 0.66 SD in girls (p < 0.01) and 0.69 SD in boys (p < 0.05). This alteration of growth affected more clearly children who became diabetic before the onset of puberty, especially those with early-onset diabetes and bad metabolic control. Growth changes for the first 5 years of diabetes were significantly and negatively correlated with mean hemoglobin A1c levels (r = -0.57). Growth changes from the onset of diabetes to the end of growth were correlated with age at diagnosis, (boys: r = 0.73; girls: r = 0.37). During puberty, girls exhibited a reduced growth spurt, especially when they were overweight and received too low doses of insulin.

CONCLUSIONS

On the whole, diabetic children were growing in normal range. Growth was adversely and mainly affected by early-onset diabetes, a long duration of disease, many years of poor metabolic control and, especially in adolescent girls, low doses of insulin and weight excess.

Insulin and insulin-like growth factor-I: their role as risk factors in the development of diabetic cardiovascular disease

Experimental data support a role for insulin and insulin-like growth factor-I (IGF-I) in the pathophysiology of vascular complications in diabetes. Clinical data for both hormones are less convincing, mainly because the various studies vary in methodologies, sample sizes, and populations. So far, by epidemiological means, insulin's vascular toxicity has been shown only in middle-aged non-diabetic men. Furthermore, serious methodological problems hamper the clear understanding of IGF-I's significance in this context. Definitive determination of the role of insulin, IGFs and other growth factors in the development of diabetic vascular complications needs considerably more work. In any case, hyperinsulinemia is associated with a cluster of other accepted risk factors for cardiovascular disease which altogether resemble the entire insulin-resistance syndrome.

Natural course of growth hormone hypersecretion in insulin-dependent diabetes mellitus

High growth hormone levels in patients with insulin-dependent diabetes were recognised 25 years ago. For many years this has been explained as an epiphenomenon of poor metabolic control. The natural course of the disease is characterised by gradual loss of residual beta-cell function and parallel elevations of plasma growth hormone and can be divided into three consecutive phases. It appears that the hormonal changes observed are determined by the IGF-1 generating capacity of the liver which, in turn, is dependent on the synergistic stimulating action of growth hormone and portal insulin. The first (initial) phase of insulin-dependent diabetes mellitus is characterised by the absence of insulin, high growth hormone levels and low plasma IGF-1. The pituitary growth hormone response to exercise and other stimuli is pathological. The second phase of disease ('C-peptide positive phase') is characterised by the return of some residual beta-cell insulin secretion, increased levels of growth hormone compared to non-diabetic subjects, physiological IGF-1 levels and near normal pituitary growth hormone responses to different agents. The third phase of the disease is characterised by complete loss of endogenous insulin secretion, very high plasma growth hormone levels, low normal plasma IGF-1 but impaired hepatic IGF-1 generating capacity. The control mechanisms of pituitary growth hormone secretion (long loop negative feedback and auto-feedback), are disturbed.

The 'dawn phenomenon' in adolescents with insulin dependent diabetes mellitus: possible contribution of insulin-like growth factor binding protein-1

OBJECTIVE

Insulin resistance increases during adolescence, and is exaggerated in patients with insulin dependent diabetes mellitus (IDDM). A relative deficiency of insulin-like growth factor-I (IGF-I) may contribute to this increased insulin requirement. Two mechanisms have been proposed: (a) increased GH secretion, caused by failure of IGF feedback control, leading to increased insulin resistance and (b) lack of insulin-like action of the IGFs which is reinforced by high plasma levels of IGFBP-1, an inhibitor of IGF action. The contribution of these two mechanisms to the 'dawn phenomenon' is assessed.

DESIGN

The two possible mechanisms were studied during the dawn rise of glucose in pubertal adolescent patients with IDDM. Two overnight studies were performed in each subject. Patients remained on the same insulin regimen throughout.

SUBJECTS

Twenty-two diabetic adolescent subjects, aged (mean +/- SEM) 14.0 +/- 0.4 years, duration of IDDM 7.9 +/- 0.8 years, were recruited. Pubertal status was: group 1 (breast stage 1-2; testicular volume < 4-8 ml) 3 male and 4 female, group 2 (breast stage 3; testicular volume 10-12 ml) 0 male 4 female, group 3 (breast stage 4-5; testicular volume 15-25 ml) 4 male and 7 female. Height standard deviation score (mean +/- SD) (-0.02 +/- 0.99) and daily insulin dose (50.4 +/- 3.1 U/day) did not change between studies. There were no differences in HbA1 (study A 11.26 +/- 0.45%, study B 11.09 +/- 0.42%).

METHODS

The subjects were admitted for the two studies 0.3 +/- 0.03 years apart. Blood samples were taken via an indwelling cannula every 20 minutes between 1900 and 0700 h.

MEASUREMENTS

GH was assayed every 20 minutes, IGFBP-1, glucose and free insulin every hour and IGF-I at 0700 h. GH, IGFBP-1, IGF-I and free insulin were measured by radioimmunoassay. IGFBPs were also analysed by Western ligand blotting techniques. GH profiles were analysed by Pulsar and results compared by paired Student's t-test. The relations between the dawn rise in glucose and the changes in IGFBP-1, GH and free insulin were examined by multiple linear regression analysis.

RESULTS

Serum IGFBP-1 levels rose overnight in the two studies (study A, from 9 +/- 1 at 2200 to 59 +/- 9 micrograms/l at 0700 h; study B, from 10 +/- 1 at 2100 to 64 +/- 14 micrograms/l at 0700 h) whilst insulin levels fell from 47 +/- 5 at 2200 to 16 +/- 2 mU/l at 0700 h (study A) and from 45 +/- 5 at 2000 to 14 +/- 2 mU/l at 0700 h (study B). Glucose levels fell from 16.0 +/- 1.0 to 9.3 +/- 0.9 mmol/l at 0400 h, and then rose to 11.9 +/- 1.1 mmol/l at 0700 h during study A, and from 13.4 +/- 1.3 to 10.1 +/- 1.1 mmol/l at 0400 h and then rose to 13.5 +/- 1.0 mmol/l at 0700 h during study B. There were no differences in GH secretion between studies (mean GH levels (mean +/- SD) (study A, 15.7 +/- 6.6 mU/l; study B, 16.2 +/- 7.1 mU/l; correlation within subjects between studies r = 0.77, P < 0.001), sum of GH peaks (study A, 189.9 +/- 90.3 mU/l; study B, 185.8 +/- 100.2 mU/l; r = 0.57, P = 0.006)). Mean GH levels varied with pubertal stage (group 1, 12.1 +/- 1.5 mU/l; group 2, 23.3 +/- 2.1 mU/l; group 3, 15.3 +/- 1.2 mU/l). Serum IGF-I levels were not different (study A, 203 +/- 12 micrograms/l; study B, 218 +/- 13 micrograms/l). REGRESSION ANALYSIS: The change in plasma glucose between 0200 and 0700 h in both studies related to free insulin, IGFBP-1 and the sum of the GH levels over the preceding hour (log glucose = 7.87 + 5.32 log IGFBP-1 (P = 0.0001) - 5.05 log free insulin (P = 0.0001) - 1.44 log GH (P = 0.004); R2 = 72%). Mean overnight GH levels did not predict the morning rise in plasma glucose.

CONCLUSION

The morning rise of IGFBP-1 and plasma glucose appear to be related in this group of subjects with IDDM and this was a consistent finding in the two studies. This relation was additive to the effect of insulin deficiency.

Does glycemic control affect growth velocity in children with insulin-dependent diabetes mellitus

To determine the effect of glycemic control on linear growth in children with insulin-dependent diabetes mellitus type 1, we studied 82 patients (40 male, 42 female) over a 6-year period. The mean +/-SD for age of onset and duration of IDDM were 7.3 +/- 3.9 years and 4.8 +/- 3.5 years, respectively. At each clinic visit, glycemic control was assessed by measuring glycosylated hemoglobin (GHb). For a total of 751 clinic visits, the mean +/- SD for chronologic age and GHb were 11.5 +/- 3.8 years and 10.2% +/- 2.3%, respectively. Good glycemic control was correlated with more frequent clinic visits (r= 0.219, P < 0.05). Growth was assessed by determining both weight and height, which were normalized for age and sex by calculating Z scores for weight and height and GHb. Moreover, regression analysis revealed no significant correlation between GHb levels and delta Z for either weight or height. While a significant correlation was observed between delta Z for weight and height (r = 0.30, P < 0.01), the relationship was not affected by glycemic control. Therefore, these data demonstrate that weight gain and growth rate do not seem to be significantly affected by glycemic control. This study also confirms that linear growth velocity is dependent on weight gain and suggests that in type 1 children, weight gain and level of growth-producing hormones such as insulin-like growth factor-1 (IGF-1) are more important regulators of linear growth than glycemic control.

Effect of recombinant human growth hormone treatment on insulin-like growth factor (IGF-I) levels in insulin-dependent diabetic patients

Basal and recombinant human growth hormone (rhGH)-stimulated insulin-like growth factor (IGF-I) levels were studied in 19 insulin-dependent diabetic patients and 4 healthy subjects. Diabetic patients were divided according to glucagon test result into CpN (10 patients without residual beta cell activity) and CpP (9 patients with preserved beta-cell activity) and CpP (9 patients with preserved beta-cell activity) groups, and according to age into three groups (A = 21-30 years; B = 31-40 years; C = 41-50 years). All control subjects belonged to group B. Blood glucose and growth hormone were measured at hourly intervals and IGF-I every 6 h during 24 h before and after 7 days treatment with 4 IU of rhGH given subcutaneously at 8 p.m. The age-related decrease in basal IGF-I levels was evident in both CpN and CpP groups of diabetic patients. IGF-I net increase with rhGH treatment was variable and insignificant in comparison with basal value without age-related differences in CpN diabetics. Progressively larger, age-related increases in IGF-I concentrations were observed in CpP diabetic patients. This study indicates impairment of hepatic IGF-I generation capacity in diabetic patients without residual beta-cell activity and the importance of simultaneous actions of portal insulin and GH on hepatic IGF-I production.

Effects of cholinergic modulation on serum insulin-like growth factor-I and its binding proteins in normal and diabetic subjects

OBJECTIVE

We wished to study alterations in serum insulin-like growth factor-I (IGF-I) and its binding proteins in subjects with insulin dependent diabetes mellitus (IDDM) and possible relations with metabolic and GH secretory status, before and after cholinergic modulation. In addition, we have investigated whether cholinergic modulation exerts any effects on IGF-I secretion, independently of any actions on GH secretory status.

DESIGN

All subjects received GH releasing hormone (GHRH) 1-44; 80 micrograms i.v.) alone and 60 minutes following 120 mg of pyridostigmine orally or 200 mg of pierenzepine orally. The three tests were carried out in random order at least one week apart. Blood was sampled at 15-minute intervals over 120 minutes.

PATIENTS

Twelve male subjects with IDDM and no clinical evidence of complications were selected on the basis of HbA1 levels to provide a wide range of metabolic control. Six normal male subjects were also studied.

MEASUREMENTS

Serum IGF-I, IGF-binding protein 1 (IGFBP-1) and IGFBP-3 were measured at regular intervals throughout the study. Fasting plasma glucose and HbA1 were measured before each study to provide measures of metabolic control.

RESULTS

Serum IGF-I and IGFBP-3 levels were significantly lower while serum IGFBP-I levels were significantly higher in the diabetic subjects. Pirenzepine had no effect on serum IGF-I, IGFBP-1 or IGFBP-3 in diabetic subjects but caused a significant increase in serum IGF-I and IGFBP-3 levels in normal subjects. Pyridostigmine had no effect on IGF-I, IGFBP-1 or IGFBP-3 in either diabetic or normal subjects. IGFBP-1 levels were significantly correlated with fasting plasma glucose but no correlation was demonstrated between measures of diabetic control and serum IGF-I or IGFBP-3 levels in diabetic subjects, nor was there any correlation between GH responses to GHRH alone or after pirenzepine or pyridostigmine pretreatment and serum levels of IGF-I, IGFBP-1 or IGFBP-3.

CONCLUSION

These data confirm that subjects with IDDM have reduced serum IGF-I and IGFBP-3 and increased IGFBP-1 levels, the latter being directly related to the fasting plasma glucose concentrations. The absence of any relation between changes in the IGF-I system and altered GH neuroregulation after cholinergic modulation suggests that changes in IGF-I are not the sole contributors to the altered GH neuroregulation which occurs in IDDM. We have also shown an acute stimulatory effect of pirenzepine on serum IGF-I and IGFBP-3 in normal subjects which is not present in IDDM although the underlying mechanisms is unknown.

Regulation of insulin-like growth factor binding protein-1 (IGFBP-1) in insulin-dependent diabetes mellitus. Effects of hyperglycaemia and insulin

The aim of the present study was to characterize the effect of 44 h of hyperglycaemia on diurnal levels of insulin-like growth factor binding protein-1 (IGFBP-1), insulin-like growth factor-1 (IGF-1), growth hormone (GH) and glucagon in 7 well-controlled subjects with insulin-dependent diabetes mellitus (IDDM). Hyperglycaemia (approximately 15 mmol/l) was induced by a glucose infusion, while the degree of insulinisation was similar to that of a corresponding period with near normoglycaemia (approximately 6.9 mmol/l). Hyperglycaemia for 44 h did not alter the normal diurnal IGFBP-1 levels when the degree of insulinisation was unchanged. The diurnal secretion pattern of IGFBP-1 was preserved in both genders and without any difference between the control and hyperglycaemic periods. However, the IGFBP-1 levels were increased in these IDDM subjects despite a peripheral hyperinsulinemia. An inverse correlation was found between IGFBP-1 and peripheral insulin levels both during periods of rapid changes in IGFBP-1 and insulin concentrations (i.e. morning hours) as well as during the total 24-h sampling period. Total IGF-1 levels were low, but no further decrease was seen after 24 h of hyperglycaemia in the presence of unchanged insulin levels. In conclusion, the present study clearly shows that the increased IGFBP-1 level seen during poor metabolic control in IDDM is not caused by hyperglycaemia. Glucose levels per se do not influence either total IGF-1 or IGFBP-1 concentrations in well-insulinised diabetic patients.

Insulin-like growth factors and binding proteins in patients with recent-onset type 1 (insulin-dependent) diabetes mellitus: influence of diabetes control and intraportal insulin infusion

Type 1 diabetes mellitus is associated with decreased insulin-like growth factor-1 (IGF-1) levels, enhanced values of growth hormone (GH) and IGF-binding protein 1 (IGFBP-1). Since the liver is the major source of IGF and IGFBP production, we have therefore examined whether levels of IGFs (IGF-1 and IGF-11) and IGFBPs (IGFBP-1 and IGFBP-3) differ when insulin is infused into the portal or peripheral vascular system. IGF, IGFBP, and GH levels were determined within 1-3 weeks of diagnosis in 36 patients (ranging in age from 18 to 22 years) with Type 1 diabetes mellitus. IGF-1 levels were low before insulin therapy administration (0.49 +/- 0.05 vs. 1.11 +/- 0.04 U/ml in controls, P < 0.01). With insulin treatment, IGF-1 levels rose to the normal range and IGF-1 normalisation depended on diabetes control and the route of insulin infusion. Diabetic patients with conventional insulin therapy (CIT; n = 12) had low IGF-1 (0.57 +/- 0.07 U/ml) compared with patients with continuous subcutaneous insulin infusion (CSII; n = 12; 0.75 +/- 0.08 U/ml; P < 0.05) and intraportal insulin infusion (IPII; n = 12; 1.07 +/- 10.05 U/ml; P < 0.05). Significant correlations were found between IGF-1 and parameters of glycemic control: HbA1c (r = -0.64; P < 0.01) and glycemia (r = -0.56; P < 0.05). The pattern of changes in IGF-11 levels was not significantly different from that of controls and was not altered by insulin therapy (0.98 +/- 0.08 and 1.01 +/- 0.04 U/ml in controls). Measured fasting 08:00 h IGFBP-1 levels were elevated 3-fold and IGFGP-3 levels were 2-fold lower in diabetic patients than in controls. Elevated IGFBP-1 levels were significantly correlated with metabolic control (glycemia, r = 0.64, P < 0.01; HbA1c, r = 0.71, P < 0.01). The mean elevated GH level before insulin administration (13.4 +/- 0.9 mg/l) was decreased by intensified insulin therapy (CSII, 8.8 +/- 0.6, P < 0.05; IPII, 5.6 +/- 0.9 mg/l, P < 0.001). There was a negative correlation between GH and IGF-1 (r = -0.72, P < 0.01). These results show the role of glycemic control and the route of insulin administration in the normalisation of IGF-1, IGFBP-1 and GH up to non-diabetic controls in patients with recent-onset Type 1 diabetes mellitus.

Urinary growth hormone measurements as a marker of renal tubular function in diabetes mellitus

Urinary growth hormone (UGH) excretion was assessed in 44 adult subjects (10 control, 21 insulin dependent diabetics (Group I), 13 diabetics in poor glycaemic control (Group II)). UGH was markedly elevated in the diabetic population. The UGH excretion in (1) control subjects ranged from undetectable levels to 0.7 microU/h, mean 0.4, (2) Group I 73-422 microU/h, mean 250 and (3) Group II 10-5,283 microU/h, mean 705. There was a significant correlation between UGH excretion and albumin excretion rate (AER) (r = 0.38, P < 0.05) in the subjects studied although only 50% of patients had an AER of > 20 micrograms/min. A stronger correlation was observed between beta 2-microglobulin and UGH excretion (r = 0.7, P < 0.01). There was no significant change in the 6-h serum GH levels following treatment in the patients in Group II. However a 23-79% decline in UGH excretion was observed following improvement of glycaemic control, although UGH levels failed to revert to normal. We conclude that the major factor responsible for increased UGH excretion in DM appears to be reduced tubular reabsorption of the hormone. This test may therefore prove useful as an additional marker for screening for diabetic nephropathy and may help in the understanding of the contribution of renal tubular abnormalities to the nephropathic process.

Insulin-like growth factor I acts as an angiogenic agent in rabbit cornea and retina: comparative studies with basic fibroblast growth factor

The release of growth factors from ischaemic retina has been hypothesized as the central stimulus for retinal neovascularization in proliferative diabetic retinopathy. Two of the growth factors implicated are insulin-like growth factor-I and basic fibroblast growth factor. We examined the effect of insulin-like growth factor-I on in vivo neovascularization using the established angiogenic model of the rabbit cornea (n = 30), and also compared the effects of insulin-like growth factor-I and basic fibroblast growth factor using two new in vivo systems. Either supraphysiologic concentrations of each growth factor (600 micrograms) were injected intravitreally into pigmented rabbits (n = 21) or porous polyfluorotetraethylene chambers filled with an emulsion containing collagen and growth factor (500 ng) were placed on the retina surface (n = 8). Our results demonstrate that when insulin-like growth factor-I was implanted together with a slow release carrier into the pocket of the normally avascular cornea, insulin-like growth factor-I (10 micrograms/pellet) induced angiogenesis in all rabbits. This degree of angiogenesis was comparable to that previously shown for basic fibroblast growth factor. For the intravitreal studies, the fibrotic component was greater in the basic fibroblast growth factor injected eyes, whereas the vascular component was accentuated in the eyes injected with insulin-like growth factor-I. Light and electron microscopy demonstrated areas of vascular proliferation in both groups. Porous polyfluorotetraethylene chamber studies with insulin-like growth factor-I and basic fibroblast growth factor demonstrated vascular proliferation in the vicinity of the chamber similar to the intravitreal injected eyes, but to a lesser degree than the injected eyes. Our experiments overall support the angiogenic potential of both insulin-like growth factor-I and basic fibroblast growth factor and support distinct but complimentary roles for each growth factor in the pathogenesis of proliferative diabetic retinopathy.

Changes in growth hormone concentrations during puberty in adolescents with insulin dependent diabetes

OBJECTIVE

To document the changes in pulsatile growth hormone secretion in diabetic adolescents during puberty, and to investigate their relationship to both metabolic control and stature.

DESIGN

Auxological parameters, overnight growth hormone secretion, fasting IGF-I, hourly glucose and metabolic control were assessed in a group of adolescents with diabetes.

PATIENTS

Fifty-two diabetic adolescents (28 males and 24 females) at different pubertal stages and with varying degrees of metabolic control were studied. Ten of those with poor diabetic control were studied on two occasions.

MEASUREMENTS

Height and weight measurements, pubertal staging, growth velocity data and bone age estimation were obtained on all the patients. Overnight growth hormone profiles (Pulsar program analysis), glycosylated haemoglobin and fasting IGF-I were performed on all the subjects. Hourly overnight glucose measurements were also obtained on the ten subjects who had two overnight growth hormone studies.

RESULTS

For the whole diabetic growth, GH area under curve (AUC) was maximal in late puberty (pubertal stage 4), and was paralleled by maximal GH peak amplitude. No relationship between GH-AUC and metabolic control was demonstrated. No difference in GH parameters was demonstrated between the male and female subgroups. The relationship between growth hormone secretory parameters and stature was not significant. However, GH-AUC was significantly correlated with growth velocity in the males but not the females.

CONCLUSIONS

The pattern of GH secretion in adolescents with diabetes parallels that seen in normal adolescents during puberty, with increases in GH concentration associated with increased GH pulse amplitude. The degree of metabolic control had no effect on this pattern and there was no relationship between GH secretory parameters and stature.

No effect of growth hormone treatment on axonal transport of slow component a in diabetic and nondiabetic rats

A decreased axonal transport of slow component a (SCa), i.e., neurofilaments, is an early event in experimental diabetes as well as hypothyroidism, and common to these metabolic derangements are decreased levels of serum insulin-like growth factor I (IGF-I). To evaluate the possible connection between these facts, we investigated the effect of growth hormone (GH), which stimulates IGF-I production, on axonal transport of SCa in diabetic and nondiabetic rats. Serum concentrations of IGF-I fell from about 1500 micrograms/L in controls to about 600 micrograms/L in diabetics. GH treatment (100 mu/rat twice daily) normalized IGF-I for the first week of diabetes, after which the level decreased to the level of the untreated diabetics. The SCa transport velocity was found to be decreased in the diabetic nerves as previously reported [0.91 +/- 0.07 = mm/day, n = 9; (mean +/- SD) versus 1.01 +/- 0.09 mm/day, n = 8, in controls, 2 p less than 0.05). No changes were seen for the GH-treated groups (1.03 +/- 0.06 mm/day, (n = 11) in GH-treated controls). The lack of effect of GH treatment can be due to blockage of IGF-I synthesis or the decreased level of thyroid hormone, triiodothyronine (T3), in the diabetic rats.

Effects of ambient glycaemic state on growth hormone responsiveness in insulin-dependent diabetes

OBJECTIVE

We wished to examine the effects of ambient glycaemia on hypothalamic somatostatinergic tone in insulin-dependent diabetes mellitus.

DESIGN

After 6-hour periods of either euglycaemia (5 mmol/l) or hyperglycaemia (15 mmol/l), exercise-induced GH secretion was measured.

PATIENTS

Seven insulin dependent diabetics with no evidence of complications were recruited.

RESULTS

There was no significant difference between basal GH levels during euglycaemia and hyperglycaemia (5.50 vs 5.53 mU/l). Nor was there a significant difference when mean delta GH levels (33.9 vs 27.4 mU/l) or mean area under GH curve (2331 vs 4038 mU min/l) during euglycaemia or hyperglycaemia were compared.

CONCLUSIONS

We find no evidence therefore to support short-term effects of ambient glucose concentration on GH responsiveness, and by inference no direct effect of short-term changes in glycaemic control on hypothalamic release of somatostatin in the aetiology of GH hypersecretion in insulin-dependent diabetes mellitus.

Resistance to the growth-promoting and metabolic effects of growth hormone in children with chronic liver disease

Because growth failure is a frequent complication of chronic liver disease in childhood, we examined the growth hormone/insulin-like growth factor type I axis and its relationship to growth disturbances, nutritional status, and carbohydrate metabolism in nine children (2.1 to 18.6 years of age) with chronic cholestatic liver disease. Seven had cholestasis associated with splenomegaly and histologic findings of cirrhosis; two patients had Alagille syndrome. Stature was less than or equal to 15th percentile in all except the youngest subject and less than 5th percentile in five subjects. Ten-hour, nocturnal, integrated serum concentrations of growth hormone were considerably higher in patients with cholestasis than in control subjects (mean +/- SD) 9.7 +/- 3.8 vs 4.7 +/- 1.9 ng/ml; p less than 0.02). Serum concentrations of insulin-like growth hormone type I were less than 95th percentile confidence intervals for age- and sex-matched norms in five patients and at the lower limits of normal in the remaining four patients. Insulin sensitivity, determined with the minimal model intravenous glucose tolerance test, was not decreased in five patients despite elevated levels of circulating growth hormone. The estimated mean caloric and protein intake exceeded the recommended dietary allowance and the weight-for-height index was greater than 90% for six of nine patients. Triceps and subscapular skin-fold thicknesses, indicators of body fat stores, were greater than 25th percentile for five of nine and eight of nine patients, respectively, suggesting deficient lipolytic action of GH. We conclude that children with cholestatic liver disease have a resistance to the growth-promoting, diabetogenic, and lipolytic properties of growth hormone.

Growth hormone and the microvascular complications of diabetes

The basis for the hypothesis that growth hormone is a permissive factor in the pathogenesis of diabetic microvascular complications is a weak one. The best way forward in this research will be to devise a pharmacological method of suppressing growth hormone secretion in diabetic subjects.

The relationship between insulin-like growth factor-I, adiposity, and aging

Aging is associated with both a relative accumulation of body fat and a reduction in growth hormone (GH) secretion. This study was devised to investigate the relationship between plasma insulin-like growth factor-I (IGF-I), an index of GH secretion, and anthropometric indices of body fat in normal subjects of various ages. Somatic and biochemical indices of nutrition were assessed in 107 subjects between the ages of 17 and 83 years who attended an outpatient clinic for general health supervision. Plasma IGF-I correlated negatively with age in both males (r = -.44, P = .001) and females (r = -.40, P = .005). In addition, plasma IGF-I correlated negatively with body mass index (BMI) (r = .35, P = .006), percentage of standard triceps skinfold (TSF) (r = -.26, P = .05), and percentage of standard weight (r = -.35, P = .006) in males, but not in females. Multiple regression analysis indicated that in males, BMI and percentage of standard weight correlated with plasma IGF-I independent of the effect of age. We conclude that adiposity and aging are independently associated with decreased plasma IGF-I concentrations. The negative correlations between indices of adiposity and IGF-I were observed only in males, whereas the age-associated decline in IGF-I was present in both males and females. We speculate that sex differences in the gonadal steroid milieu, combined with declining GH secretion in both sexes, may contribute to the age-associated development of obesity in males.

Effects of improved blood glucose on insulin-induced hypoglycaemia, TRH, GnRH and exercise tests in insulin-dependent diabetes

In order to evaluate effects of metabolic control on pituitary function in insulin-dependent diabetes exercise, hypoglycaemia (insulin tolerance test), thyrotrophin releasing hormone and gonadotrophin releasing hormone, tests were performed on 25 patients before (Study 1) and after 2 weeks of improved metabolic control (Study 2). Patients were sub-divided into C-peptide negative (CpN, 10 patients with no residual C-peptide secretion) and C-peptide positive (CpP, 15 patients with residual beta-cell function) groups for analysis of results. Exercise induced higher growth hormone responses in CpN patients independent of metabolic control (P less than 0.001). Thyrotrophin releasing hormone induced higher growth hormone responses in CpN patients; this response was threefold greater after improved control (P less than 0.005). Growth hormone and cortisol response to hypoglycaemia and thyroid stimulating hormone and prolactin secretion in response to thyrotrophin releasing hormone were unaffected by residual beta-cell function or metabolic control. Luteinizing hormone response to gonadotrophin releasing hormone in CpN patients was impaired and lower after improved control (P less than 0.002). The results indicate an association between residual pancreatic insulin secretory and hypothalamic/pituitary function, possibly reflecting central neurosecretion of insulin.

The effects of improved blood glucose on growth hormone and cortisol secretion in insulin-dependent diabetes mellitus

Growth hormone and cortisol secretion were studied in 25 patients with insulin-dependent diabetes before (Study 1) and 2 weeks after improved glucoregulation (Study 2). Blood samples for serum growth hormone (GH) and blood glucose determination were collected at hourly intervals whilst blood samples for cortisol and C-peptide were collected every 6 h during the 24-h period in Study 1 and Study 2. Glycaemic control was significantly improved in Study 2 compared to that in Study 1 (8.5 vs 13.3 mmol/l; P less than 0.001). With improved control, growth hormone levels rose by 21% (5.7 vs 4.7 mU/l; P less than 0.05). Throughout both study periods growth hormone levels were higher in patients with no residual C-peptide secretion (10 CpN patients) compared with patients with residual beta-cell function (15 CpP patients) (7.1 vs 3.2 mU/l in Study 1; 8.9 vs 4.2 mU/l in Study 2; P less than 0.001). Characteristic shapes of the 24-h blood glucose profile curves during both study periods were significantly different between the CpN and CpP group. Plasma cortisol decreased in both groups with improved metabolic control (P less than 0.001) but the observed different diurnal pattern did not change. These results demonstrate the importance of residual endogenous insulin secretion in determining growth hormone secretion in insulin-dependent diabetes and have important implications for glycaemic control and risk of microvascular complications.

The effect of ovarian function on insulin-like growth factor I plasma levels and hepatic IGF-I mRNA levels in diabetic rats treated with insulin

When insulin was administered to streptozotocin-induced diabetic female rats, the percentage of glycohemoglobin, growth rate, ovulatory cycle, uterus to body weight ratio, and insulin-like growth factor (IGF-I) level returned to near normal. In untreated diabetic rats there were no normal estrous cycles, and hepatic IGF-I mRNA (7.94 +/- 1.02 O.D. units per micrograms total RNA) levels were significantly lower than the control or insulin-treated groups in proestrus (16.47 +/- 0.91 and 17.15 +/- 1.84, respectively). Insulin therapy restored the hypothalamic-pituitary-ovarian axis with the reinstitution of normal estrous cycles. Plasma IGF-I levels were highest in non-diabetic proestrous animals (277 +/- 36.9 ng/ml), significantly higher than IGF-I levels in insulin-treated diabetic rats in diestrus (174 +/- 23.1 ng/ml), non-diabetic diestrus rats (165 +/- 18.4 ng/ml) and untreated diabetic rats (135 +/- 19.7 ng/ml). Plasma IGF-I levels were elevated in insulin-treated diabetic rats in proestrus (221 +/- 78.3 ng/ml), however this was not significantly different from any other group. The increases observed in plasma IGF-I and hepatic IGF-I mRNA after insulin therapy correlate with the normalization of sex hormone secretion. Though this study does not prove a causal relationship between restoration of ovarian function and normalization of circulating IGF-I levels, a relationship has been established, as evidenced by higher levels of IGF-I in both the control and insulin-treated diabetic proestrous groups when compared to the diestrus groups.