Administration of human recombinant insulin-like growth factor-I to patients following major gastrointestinal surgery

OBJECTIVE: The aim was to study the pharmacokinetic parameters and biological activity of a single dose of human recombinant IGF-I (rhIGF-I) administered to patients following major gastrointestinal surgery. DESIGN: A double blind placebo controlled externally randomized study of 30 patients; the study commencing 24 hours after major colonic or gastric surgery. MEASUREMENTS: After a baseline blood sampling day, IGF-I (40 micrograms/kg by single subcutaneous dose, n = 20) or placebo (n = 10) was administered and serum and urine samples collected over the ensuing 72 hours. Serum IGF-I, IGF-II, IGF binding proteins (IGFBP-1, IGFBP-3), GH and insulin were measured by radioimmunoassay. Serum IGF bioactivity was assessed using a validated porcine cartilage bioassay. Serum and urinary electrolytes were measured by standard methodology. RESULTS: Serum immunoreactive IGF-I levels peaked at 4 hours following injection of IGF-I (1.09 +/- 0.12 U/ml mean +/- SEM), remained elevated for 15 hours and returned to basal levels by 24 hours after injection. IGF bioactivity was increased by 57% 6 hours after IGF-I injection. Mean levels of IGFBP-1 and IGFBP-3, IGF-II and GH were unaffected by IGF-I administration. Insulin levels were suppressed at 30 minutes following injection of IGF-I compared with the placebo group (16.9 +/- 3.0 mU/I vs 32.3 +/- 7.1, P = 0.02); thereafter, there were no differences in insulin levels. The mean change in serum creatinine following IGF-I (-6.3 +/- 3.0 mmol/l) was significantly different from that in the control group (+7.2 +/- 6.2, P = 0.03). Creatinine clearance rose from a mean of 71.6 +/- 7.5 ml/min to 83.2 +/- 7.6 ml/min after IGF-I treatment (P = 0.02). In the IGF treated patients, cholesterol levels consistently fell (-0.20 +/- 0.05 mmol/l); this was not observed in the placebo group (+0.20 +/- 0.14, P = 0.006). Basal serum potassium levels in the IGF treatment group (4.1 +/- 0.1 mmol/l) fell to 3.8 +/- 0.1 at 4 hours (P = 0.002) and 3.6 +/- 0.1 at 10 hours (P = 0.001) returning to a level of 4.0 +/- 0.1 (P = 0.293) at 24 hours after injection. There were no other observed differences in serum or urinary electrolytes or serum free fatty acids and triglycerides. Pharmacokinetic parameters derived from baseline adjusted IGF-I measurements revealed a slow absorption of the administered dose with a Tmax of 5.0 +/- 0.43 hours and an elimination half-life of 10.8 +/- 1.2 hours. The computed volume of distribution was 0.33 +/- 0.05 I/kg and the clearance on average 25 ml/min. CONCLUSION: A single subcutaneous dose of IGF-I normalized circulating IGF-I levels in post-operative patients, was well tolerated and without side-effects. IGF bioactivity was increased and associated with a fall in serum cholesterol, potassium and creatinine levels and a rise in creatinine clearance. Further long-term studies are now required to assess the anabolic effects of rhIGF-I in this type of patient group.     

Recombinant human insulin-like growth factor-I (rhIGF-I) therapy in adults with type 1 diabetes mellitus: effects on IGFs, IGF-binding proteins, glucose levels and insulin treatment

OBJECTIVE: Insulin-like growth factor-I (IGF-I) has both insulin-like and anabolic actions but unlike insulin, IGF-I circulates bound to a number of specific binding proteins that regulate its availability and activity. Patients with type 1 diabetes mellitus have low levels of circulating IGF-I despite increased growth hormone (GH) secretion, and are a group that may benefit from rhIGF-I therapy. Understanding the relationship between IGF-I and its binding proteins is necessary to appreciate the actions of exogenously administered rhIGF-I. Therefore, we examined the effects of 19 days' subcutaneous administration of rhIGF-I (50 micrograms/kg BID) on the levels of IGF-I, IGF-II and the IGF-binding proteins (IGFBPs), as well as the daily dose of insulin necessary to maintain glycaemic control in patients with type 1 diabetes mellitus. DESIGN AND PATIENTS: This was an open study, and the patients were studied initially while resident (days 1-5) in the hospital and thereafter (days 6-24) as outpatients. Serum was collected at baseline and at intervals throughout the study for the measurement of total IGF-I, IGF-II, IGFBP-1, -2, -3, free insulin and growth hormone (GH). Daily insulin doses and glucometer readings were recorded throughout the study. The changes in each of these variables were examined. The subjects were six adults (35.3 +/- 4.0 years, mean +/- SE), with type 1 diabetes, and all had reasonable glycaemic control (HbA1c 7.2 +/- 0.5%). RESULTS: rhIGF-I administration increased circulating total IGF-I over two-fold (15.3 +/- 1.9 vs. 33.7 +/- 5.4 nmol/l, mean +/- SEM, P < 0.01, day 1 vs. day 20) and decreased plasma IGF-II concentration (85.0 +/- 4.7 vs. 50.6 +/- 4.7 nmol/l, P < 0.01, day 1 vs. day 20). The dose of insulin required for adequate glycaemic control decreased significantly during rhIGF-I therapy (46 +/- 7 vs. 31 +/- 8 U/day, P < 0.05, day -1 vs. day 19), as did the fasting free insulin concentration (8.4 +/- 1.5 vs. 5.0 +/- 0.8 mU/l, P < 0.05, baseline vs. day 5). IGFBP-2 concentration increased (388 +/- 115 vs. 758 +/- 219 micrograms/l, P < 0.05, day 1 vs. day 20), but IGFBP-1 and IGFBP-3 were unchanged during rhIGF-I treatment. Mean nocturnal GH concentration decreased (12.7 +/- 3.3 vs. 3.8 +/- 0.9 mU/l, P = 0.05) after 4 days' rhIGF-I therapy. CONCLUSION: Twice daily rhIGF-I therapy in adults with type 1 diabetes resulted in an increase in circulating IGF-I with a reciprocal decrease in IGF-II, and a marked elevation of IGFBP-2 concentration. The levels of IGFBP-1 and -3 were not dramatically changed despite a reduction in the concentration of serum free insulin, and a large decrease in the requirement for insulin. The mechanisms behind these changes remains unclear but alterations in circulating levels of of IGFBPs may alter IGF-I bioactivity. If rhIGF-I is to have an application in the management of adults with type 1 diabetes, further work is necessary to determine the metabolic consequences of the alterations seen in the IGFs and their binding proteins following rhIGF-I administration.     

Effect of thyroxine administration on the IGF/IGF binding protein system in neonatal and adult thyroidectomized rats

The effects of different doses of thyroxine (T(4)) delivered by injection or s.c. pellet implantation on alterations of the IGF/IGF binding protein (IGFBP) system were studied in neonatal and adult thyroidectomized (Tx) rats. Body weight, blood glucose, plasma insulin, TSH and GH and pituitary GH content, as well as serum IGF-I, IGF-II, IGFBP-1, -2 and -3 and their liver mRNA expression were assayed. Pellet implantation with the smaller dose of T(4) (1.5 microg/100 g body weight (b.w.) per day) in Tx neonatal rats decreased serum IGF-I, -II and the 30 kDa complex of IGFBPs (IGFBP-1 and -2), and increased serum IGFBP-3. Only the larger dose of T(4) (3 microg/100 g b.w. per day) recovered liver mRNA expression of IGF-I and ensured euthyroid status as shown by the normalized levels of plasma TSH. The rapid increase of body weight and serum GH after T(4) administration indicated a high sensitivity to T(4) during the neonatal period. Serum and liver mRNA expression of IGFs and plasma insulin and GH recovered in adult Tx rats after pellet implantation of 1.75 microg/100 g b.w. per day throughout 10 days. The continuous replacement of T(4) by pellet seems to be the most suitable method for thyroid rehabilitation. A very good correlation was found between insulin and IGF-II in Tx neonates treated with T(4) but not between insulin and IGF-I in Tx adults. IGFBP-2 seems to be up-regulated by T(4) deprivation in neonatal and adult rats. Finally, a good correlation as well as a partial correlation were found between IGFs and thyroid hormones in both neonatal and adult Tx populations, suggesting a direct effect in vivo of T(4) on the hepatic secretion of IGFs, as previously suggested in vitro.     

Effects of recombinant human insulin-like growth factor-I (rhIGF-I) on total and free IGF-I concentrations, IGF-binding proteins, and glycemic response in humans.

To examine the effects of repeated administration of recombinant human insulin-like growth factor-I (rhIGF-I) on IGF-I levels, free IGF-I pharmacokinetics, glycemic response, and IGF-binding proteins (IGFBP), we administered rhIGF-I (0.03 mg/kg iv bolus) to 12 healthy males each morning for 5 consecutive days. Serum was collected over 24 h on days 1 and 5 for measurement of total and free IGF-I, glucose, insulin, and IGFBP. Total IGF-I was measured by RIA after acid/ethanol extraction. Free IGF-I was separated from binding protein-complexed IGF-I using size exclusion high performance liquid chromatography before measurement by RIA. IGFBP were quantitated by optical densitometry of Western ligand blots. Total IGF-I increased significantly from 0-24 h after administration on day 1 (mean +/- SD, micrograms/L: 120 +/- 44 to 166 +/- 51, P = 0.0002) but did not increase significantly from 24 h on day 1 to 0 h on day 5 (166 +/- 51 to 178 +/- 62) or from 0-24 h on day 5 (178 +/- 62 to 209 +/- 89). The area under the total IGF-I concentration curve was greater on day 5 than day 1 (311 +/- 99 min.g/L vs. 249 +/- 77, P = 0.0001). There were no significant differences in free IGF-I concentration or pharmacokinetic parameters or in the degree or timing of hypoglycemia between days 1 and 5. Plasma insulin levels decreased significantly following rhIGF-I administration (day 1 baseline: 53 +/- 11 pmol/L, nadir: 18 +/- 6 pmol/L at 30 min, P = 0.003); day 5 baseline: 47 +/- 15 pmol/L, nadir: 16 +/- 8 pmol/L at 30 min, P = 0.0003. Western ligand blotting revealed the transient appearance of a 30-kilodalton band which migrates in a manner similar to IGFBP-1. This band was undetectable at baseline, peaked between 150 and 210 min after rhIGF-I administration, and diminished by 480-600 min. The response was similar on days 1 and 5. There were no substantial changes in the serum levels of any other IGFBP. In summary, repeated iv bolus administration of rhIGF-I increased the level of total circulating IGF-I without changing free IGF-I disposition or glycemic response. A 30-kilodalton IGFBP band, most likely IGFBP-1, appeared transiently following rhIGF-I administration, probably as a result of suppression of insulin levels. IGFBP-2, -3, and -4 were unaffected.     

Effects of a 7-day continuous infusion of octreotide on circulating levels of growth factors and binding proteins in growth hormone (GH)-treated GH-deficient patients

In patients with acromegaly, clinical improvement has been reported after octreotide (OCT) treatment, even in cases of only a moderate suppression of growth hormone (GH) levels. In rats, OCT suppresses IGF-I mRNA expression and generation of serum and tissue IGF-I levels. A direct effect of OCT on the IGF system could have therapeutical implications in diabetes mellitus, cardiovascular disease, and certain malignancies in which IGF-I might be involved. The aim of this study was to examine possible GH-independent effects of OCT on IGF components in humans. Six GH-deficient (GHD) patients were studied for 24 h after each of the following treatment regimens (each of 1 weeks duration): (a) daily s.c. GH injection (2 IU/m(2)); (b) as (a) + continuous s.c. infusion of OCT (200 microg/24 h) by means of a portable pump (Nordic Infuser); (c) no treatment. Serum GH binding protein (GHBP) levels tended to be lower after GH and OCT than after GH alone (P =0.10). OCT reduced the GH induced increase in serum IGF-I levels (P<0.05, ANOVA). Mean integrated levels (microg/l) were 359.1+/-49.6 (GH), and 301.6+/-58.9 (GH+OCT). OCT did not significantly reduce serum IGFBP-3 levels (microg/l) [3460+/-270 (GH), and 3112+/-435 (GH+/-OCT);P =0.14]. Serum levels of free IGF-I (P =0.39), IGF-II (P =0.54), and of the acid-labile subunit (ALS) of the ternary complex (P =0.50) were similar during GH+/-OCT as compared with GH alone. After 1 week off GH treatment, significantly lower levels of IGF-I, IGF-II, IGFBP-3, and ALS were recorded (P<0.001). Serum IGFBP-1 levels were significantly higher after GH+OCT than after GH alone (P<0.0001), and levels were even higher without GH. Serum insulin levels (pmol/l) were significantly higher after GH alone as compared with no GH (P<0.05, ANOVA), whereas OCT partly suppressed the insulinotropic effect of GH (P<0. 05) [mean: 114.5+/-33.0 (GH), 91.3+/-29.6 (GH+OCT), 65.9+/-22.5 (no GH)]. This was also reflected in higher blood glucose levels during GH+OCT. Finally, GH+OCT reduced glucagon levels significantly as compared with GH alone (P =0.02). In conclusion, 7 days' administration of OCT to GH-treated GHD patients slightly attenuated serum IGF-I generation, and tended to decrease levels of the other components of the 150 kDa ternary complex. Whether these effects are mediated directly by OCT or indirectly via the accompanying changes in insulin levels remains to be investigated.     

Effects of recombinant human insulin-like growth factor I (IGF-I) therapy on the growth hormone-IGF system of a patient with a partial IGF-I gene deletion.

We have previously reported a 17.2-yr-old boy with severe growth retardation and undetectable serum levels of insulin-like growth factor I (IGF-I) due to a partial deletion of the IGF-I gene. The aim of this study was to investigate the effects of recombinant human IGF-I (rhIGF-I) therapy on the GH-IGF system of this patient to gain further insights into its growth-promoting and metabolic actions. To assess the changes in GH, IGFs, IGF-binding proteins (IGFBPs), acid-labile subunit (ALS), and insulin levels, blood samples were obtained before therapy and during the first year of treatment. Hormones were analyzed by specific RIAs. Overnight GH profiles were performed before and at 1, 6, and 12 months of therapy. Fasting ALS, IGF-II, IGFBP-3, IGFBP-2, IGFBP-1, and insulin levels before rhIGF-I treatment were 46.3 mg/L, 1044 microg/L, 5.8 mg/L, 73 ng/mL, 4.7 ng/mL, and 27.3 mU/L, respectively. IGF-II, ALS, and insulin levels were elevated, whereas IGFBP-1 and IGFBP-2 levels were decreased compared to reference values. Twenty-four hours after a single s.c. injection of rhIGF-I (40 microg/kg), the concentrations were 46 mg/L, 888 microg/L, 6.9 mg/L, 112 ng/mL, 5.0 ng/mL, and 21.0 mU/L, respectively. After a single s.c. injection of rhIGF-I of 40 or 80 microg/kg x day and modelling the data using a two-compartment model, the half-lives of elimination were 15.7 and 14.3 h, with a maximum increase in IGF-I levels to 341 and 794 microg/L around 7 h, respectively. An increase in IGFBP-3 levels was observed with both doses of rhIGF-I, with a peak values of 9 mg/L. GH profiles showed a decrease in peak amplitude from 342 to 84 mU/L at 1 month, to 67 mU/L at 6 months, and to 40 mU/L at 1 yr of therapy, with no significant changes in peak number. A significant increase in IGFBP-1 levels was observed during treatment with 80 microg/kg x day IGF-I, reflecting the inhibitory effect of rhIGF-I on insulin secretion. The clinical response to rhIGF-I therapy was an increased height velocity from 3.8 cm/yr before treatment to 6.6 cm/yr. Increased lean body mass correlated with changes in the doses of rhIGF-I and, in turn, with the biochemical changes in the GH-IGF axis. Similar to healthy individuals, this patient had normal IGFBP-3 and ALS levels, which are the major regulators of the pharmacokinetics of rhIGF-I. In summary, rhIGF-I treatment has improved linear growth and insulin sensitivity in this patient by restoring IGF-I levels and by normalizing circulating GH, IGFBP, and insulin levels.     

The effect of anorexia nervosa and refeeding on growth hormone-binding protein, the insulin-like growth factors (IGFs), and the IGF-binding proteins.

We studied the relationship of serum insulin-like growth factor-I (IGF-I), IGF-II, the IGF-binding proteins IGFBP-1, IGFBP-2, and IGFBP-3, and GH-binding protein (GHBP; which is postulated to be derived from the extracellular portion of the GH receptor) in normal volunteers and patients with anorexia nervosa before and after a refeeding program. Serum GHBP, IGF-I, and IGFBP-3 were all significantly decreased in low weight patients with anorexia nervosa and returned to nearly normal levels with refeeding. Fasting serum GH and serum IGFBP-1 and IGFBP-2 were significantly increased in low weight patients with anorexia nervosa and also returned to nearly normal levels with refeeding. Serum IGF-II was 27% lower in the low weight group than in normal subjects, but this difference was not statistically significant. Both serum IGF-I and IGF-II were positively correlated with serum IGFBP-3 and negatively correlated with serum IGFBP-1 and IGFBP-2. These data are consistent with the hypothesis that nutritional deprivation alters the GH-IGF axis by down-regulation of the GH receptor or its postreceptor mechanisms, and that this effect is reversible with refeeding.     

Short-term changes in serum insulin-like growth factors (IGF) and IGF binding protein 3 after different modes of intravenous growth hormone (GH) exposure in GH-deficient patients.

Virtually all circulating insulin-like growth factors I and II (IGF-I and IGF-II) are bound to specific binding proteins (IGFBP), of which IGFBP-3 is the quantitatively most important. The mechanisms regulating the close coordination between serum levels of IGFs and IGFBP-3 is poorly understood. We therefore evaluated the temporal association of serum IGF-I, IGF-II, and IGFBP-3 measured by RIAs after well defined short-term GH exposure in GH-deficient patients. Six patients (mean +/- SE age: 20.5 +/- 1.1 yr) each underwent three GH study protocols in random order. Each study was preceded by 4 weeks without GH therapy. Two units of GH were administered iv as either: 1) two boluses, 2) eight boluses, or 3) a constant infusion. The duration of each study was 44 h including at least 16 h after termination of GH administration. Increments in serum IGF-I occurred 4-6 h after initiated GH exposure in all studies. In the two-bolus study the IGF-I increase was modest with mean +/- SE peak values of 12.4 +/- 2.1 nmol x L-1 after GH administration. In the eight bolus and constant infusion studies significantly higher IGF-I levels were generated: 17.0 +/- 2.2 nmol x L-1 (8 bolus) and 18.8 +/- 1.1 h nmol x L-1 (infusion). In contrast the time course change in serum IGF-II did not differ in the three studies, and it was characterised by a sluggish increase of approximately 30% evidenced after 16-20 h. The changes in IGFBP-3 were almost identical in the three studies. After a lag phase of approximately 18-20 h a gradual increase of approximately 40%, which had not ceased at the end of the study period, was observed. The molar ratio of serum IGF-I plus IGF-II:serum IGFBP-3 remained constant with values between 0.8-0.9 except in the constant infusion experiment, in which the ratio increased significantly with time reaching a mean peak value, which exceeded 1.0, after 24 h. Our data suggest that a pulsatile GH pattern is not superior to constant GH levels as regards generation of IGFs and IGFBP. The earlier increase in serum IGF-I compared to IGF-II and IGFBP-3 suggests that IGF-I may be the main regulator of IGFBP-3 production. Accordingly, the slow increase in serum IGF-II, which paralleled that of IGFBP-3, could indicate that serum IGF-II levels mainly depend on the concentration or binding site availability of IGFBP-3.     

Pharmacokinetic studies of recombinant human insulin-like growth factor I (rhIGF-I)/rhIGF-binding protein-3 complex administered to patients with growth hormone insensitivity syndrome

CONTEXT: GH insensitivity syndrome (GHIS), Laron syndrome, is characterized by severe short stature, high serum GH levels, and very low serum IGF-I and IGF-binding protein-3 (IGFBP-3) levels associated with a genetic defect of the GH receptor. Recombinant human (rh) IGF-I treatment at doses of 80-120 microg/kg given sc twice daily is effective in promoting growth in these patients. We have investigated a newly developed drug, rhIGF-I/rhIGFBP-3, a 1:1 molar complex of rhIGF-I and rhIGFBP-3. OBJECTIVES: The objectives of the study were to determine IGF-I pharmacokinetics after the administration of rhIGF-I/rhIGFBP-3 in adolescents with GHIS and to evaluate its safety and tolerability. DESIGN: This was an open-label clinical study. SETTING: The study was conducted in a general pediatric ward of a university teaching hospital. PARTICIPANTS: Four patients (one female and three males; mean age, 14.9 yr; mean height sd score, -4.9) with confirmed molecular diagnosis of GHIS agreed to participate in the study. INTERVENTION: rhIGF-I/rhIGFBP-3 was administered in a single sc injection at 0.5 and 1.0 mg/kg.dose (equivalent to 100 and 200 microg/kg rhIGF-I) after breakfast with a 2-d interval between doses. RESULTS: IGF-I levels reached a maximum between 19 +/- 8.3 and 15 +/- 6.2 h for the low and high doses, respectively. The circulating IGF-I levels obtained with the low and high doses were similar, although a discrete dose-dependent increase in circulating IGF-I levels was observed. The IGF-I half-life in four subjects after a dose of 0.5 mg/kg rhIGF-I/rhIGFBP-3 was estimated to be 21+/- 4 h. There were no acute adverse events reported, and all blood glucose measurements were normal. CONCLUSION: These data demonstrated that the rhIGF-I/rhIGFBP-3 complex was effective in increasing levels of circulating total and free IGF-I into the normal range for a 24-h period after a single sc administration in patients with GHIS, and that administration of rhIGF-I/rhIGFBP-3 was safe and well tolerated.     

Effect of chronic thyroxine treatment on IGF-I, IGF-II and IGF-binding protein expression in mammary gland and liver during pregnancy and early lactation in rats

OBJECTIVE: Hyperthyroidism in rats produces organ hypertrophy and increases in circulating IGF-I and IGF-binding protein (IGFBP)-3. Chronic treatment with thyroxine (T(4)) during pregnancy advances parturition, blocks lactation and changes several hormone receptors in mammary gland and liver. Since IGFs are implicated in mammary and liver growth and in differentiation, we studied the effects of hyperthyroidism, induced by daily injections of T(4) (0.25 mg/kg). DESIGN AND METHODS: Using quantitative RT-PCR and in situ hybridization, the gene expression of IGF-I, IGF-II and the IGFBPs was determined in mammary gland and liver of rats at estrus and days 7, 14 and 21 of pregnancy (G7, G14, G21), day 1 postpartum (L1) and 3 days after removing the litter (L4). Circulating levels of IGF-I, tri-iodothyronine (T(3)), PRL and GH were measured. RESULTS: T(4) treatment (HT) increased circulating T(3) save on G21, did not change serum IGF-I, increased PRL on G21 and decreased GH on L1. PRL decreased on L1 because of the absence of lactation. Hepatic IGF-I mRNA was low during pregnancy and increased on L4. HT advanced this increase to L1. In controls, liver IGFBP-3 mRNA levels decreased from G14 to G21, whereas IGFBP-4 showed an inverse pattern. HT lowered IGFBP-3 mRNA and increased IGFBP-4. Increases in mammary concentrations of IGF-I, IGFBP-3 and IGFBP-4 mRNAs were seen on G21. HT delayed these peaks to L1. Mammary IGF-II and IGFBP-2 mRNA levels were high on G7 and G14, and fell afterwards, with HT having no effects. IGFBP-5 mRNA decreased during pregnancy and increased on L1. HT increased IGFBP-5 levels in early pregnancy and on L1. IGF-I mRNA localized to connective and epithelial mammary tissue, while IGFBP-2 and IGFBP-5 mRNA was only in epithelial cells. CONCLUSION: These results imply a role for IGF-I, IGFBP-3 and IGFBP-4 in terminal mammary development, while IGF-II and IGFBP-2 may be implicated in early growth. IGFBP-5 has been implicated in mammary apoptosis, and the HT-induced increase may play a role in the premature mammary involution of the HT rats.     

Dose-dependent effects of recombinant human insulin-like growth factor (IGF)-I/IGF binding protein-3 complex on overnight growth hormone secretion and insulin sensitivity in type 1 diabetes

GH hypersecretion in type 1 diabetes has been implicated in the pathogenesis of insulin resistance, and microangiopathic complications, and may result from reduced circulating IGF levels. We examined the effects of recombinant human (rh)IGF-I [complexed in equimolar ratio with rhIGF binding protein (BP)-3 (rhIGF-I/IGFBP-3)] replacement on overnight GH levels and insulin sensitivity in type 1 diabetes. Fifteen subjects, 13-24 yr old (10 male), were given rhIGF-I/IGFBP-3 or placebo as a daily sc injection for 2 d. After the second injection overnight, insulin requirements for euglycemia were determined (0400-0800 h), followed by a 4-h, two-step (insulin, 0.6 and 1.5 mU/kg.min) hyperinsulinemic euglycemic [90 mg/dl (5 mmol/liter)] clamp. In each subject, the protocol was repeated on three occasions in random order. Seven subjects received placebo and rhIGF-I/IGFBP-3 (0.1 mg/kg.d and 0.4 mg/kg.d), and eight subjects received placebo and rhIGF-I/IGFBP-3 (0.2 mg/kg.d and 0.8 mg/kg.d). We found dose-dependent increases in circulating IGF-I and IGFBP-3 concentrations after rhIGF-I/IGFBP-3. These were paralleled by significant reductions in mean overnight GH levels and GH pulse amplitude. We also observed dose-dependent effects of rhIGF-I/IGFBP-3 on overnight insulin requirements for euglycemia, with reductions of up to 41%. Insulin sensitivity, defined by M-values, was improved with rhIGF-I/IGFBP-3 (0.4 and 0.8 mg/kg.d). Thus, restoration of circulating IGF-I and IGFBP-3 levels with rhIGF-I/IGFBP-3 suppresses GH secretion in adolescents with type 1 diabetes, leading to reduced insulin requirements and improvements in insulin sensitivity.     

The effect of recombinant IGF-I on anterior pituitary function in healthy volunteers

OBJECTIVE Insulin-like growth factor-I is the mediator of many of the actions of GH and is a potent metabolic regulator. Recombinant IGF-I (rhIGF-I) is of potential value in the treatment of syndromes associated with either GH or insulin resistance. This study was designed to assess the effects of subcutaneous (s.c.) rhIGF-I on anterior pituitary function. DESIGN Double-blind, placebo controlled, randomized cross-over study. The interval between investigations was 2 weeks. SUBJECTS Twelve normal volunteers received on one occasion a single S.C. dose of 40 μg/kg rhIGF-I and on the other, placebo. MEASUREMENTS Circulating levels were measured, over 24 hours, of GH, LH, FSH, PRL, TSH, cortisol, ACTH, glucose, IGF-I, IGF-II, Insulin, C-peptide; IGF binding proteins by Western ligand blotting; total IGF bioactivity using FRTL-5 thyroid cells; and glucose by the glucose oxidase method. RESULTS Recombinant IGF-I Increased AUC for plasma IGF-I, measured by radioimmunoassay (rhIGF-I mean 7065 ± SEM 33 vs 3895 ± 204 μg/l, P < 0·0001) and IGF bioactivity (22·5 ± 3·4 vs 14·2 ± 1·8 U/ml, P < 0·001) but plasma IGF-II fell (9308 ± 403 vs 11052 ± 451 μg/l, P < 0·0001). There was no biochemical or clinical evidence of hypoglycaemia and no difference in mean glucose levels. No difference existed in AUC for GH, LH, FSH, ACTH and cortisol between rhIGF-I and placebo; additionally, pulse number and amplitude for GH and LH were unaffected. TSH fell following rhIGF-I (33·0 ± 3·36 vs 42·5 ± 5·98 mU h/l, P= 0·01). Both mean plasma C-peptlde (0·73 ± 0 06 vs 0·91 ± 0±05 nmol/l, P= 0·03), and insulin (10·81 ± 1·02 vs 15·36 ± 1·18 mU/l, P= 0·03) were lower following rhIGF-I. There was no change In IGFBPs. CONCLUSION A single injection of 40 μg/kg of subcutaneous rhIGF-I does not cause hypoglycaemia. IGF bioactivity was increased without inhibition of GH secretion. The only change observed in anterior pituitary function was a fall in plasma TSH.     

Effects of combined recombinant insulin-like growth factor (IGF)-I and IGF binding protein-3 in type 2 diabetic patients on glycemic control and distribution of IGF-I and IGF-II among serum binding protein complexes

CONTEXT: Administration of recombinant human IGF-I (rhIGF-I)/recombinant human IGF binding protein-3 (rhIGFBP-3) to patients with type 2 diabetes improves blood glucose and enhances insulin sensitivity. The changes in various components of the IGF system that occur in response to rhIGF-I/rhIGFBP-3 as well as the minimum effective dose have not been determined. OBJECTIVES: The aim was to determine the dose of rhIGF-I/rh-IGFBP-3 necessary to achieve a significant decrease in glucose and to determine the changes that occur in the IGF-II and acid labile subunit in response to treatment. DESIGN: A total of 39 insulin-requiring type 2 diabetics were randomized to placebo or one of six groups that received different dosages of rhIGF-I/rhIGFBP-3. After 3 d in which insulin doses were adjusted to improve glucose control, a variable insulin dosage regimen was continued, and either placebo or one of six dosages (0.125-2.0 mg/kg.d) of rhIGF-I/rhIGFBP-3 was administered for 7 d. All subjects were hospitalized, and dietary intake as well as insulin dosage were controlled with instructions to treat to normal range targets. RESULTS: Fasting glucose was reduced in the groups that received either 1 (32 +/- 5% reduction) or 2 mg/kg.d (40 +/- 6% reduction) of the complex. Mean daily glucose (four determinations) was reduced by 26 +/- 4% in the 1 mg/kg group and by 33 +/- 5% in the 2 mg/kg group compared with 18 +/- 4% in the placebo group. Total serum IGF-I increased between 2.0 +/- 0.3- and 5.7 +/- 1.3-fold by d 8. IGFBP-3 concentrations increased significantly only in the 2 mg/kg group. IGF-II concentrations declined to values that were between 27 +/- 4% and 64 +/- 7% below baseline. Acid labile subunit concentrations declined significantly in the three highest dose groups. The sum of the IGF-I + IGF-II concentrations was significantly increased at the two highest dosages. There were very few drug-associated adverse events reported in this study with the exception of hypoglycemia, which occurred in 15 subjects who had received rhIGF-I/rhIGFBP-3 treatment. CONCLUSIONS: Administration of rhIGF-I/rhIGFBP-3 resulted in a redistribution of the amount of IGF-I and IGF-II that bound to IGFBP-3. Fasting and mean daily blood glucose were reduced significantly in the two highest dosage groups. The results suggest that both the total concentration of IGF-I as well as its distribution in blood may determine the extent to which insulin sensitivity is enhanced.     

The effect of 3,5,3'-triiodothyronine or thyrotropin-releasing hormone on pituitary hormone responses to arginine infusions in hypothyroid patients

Serum PRL and GH responses to a control arginine infusion were determined in seven hypothyroid patients. During the infusion, basal TSH levels fell slightly but significantly. On a following day, a second arginine infusion was performed, 5 min after iv injection of 500 micrograms TRH. The mean peak PRL response was enhanced 6-fold and occurred earlier, while the mean peak GH response remained unaffected. Mean peak TSH levels were only 128% above baseline after TRH. On a third day, a third arginine infusion was performed 4 h after oral administration of 100 micrograms T3; mean serum T3 levels were increased from 57 to a peak of 481 ng/dl 5 h after T3. The mean GH response was significantly reduced by 71% at 90 min, with an overall reduction of the GH output of 47%, while the PRL response remained unaffected. Thus, acute elevation of serum T3 levels in hypothyroidism appear to inhibit the mean GH response to arginine.     

The ratio between serum levels of insulin-like growth factor (IGF)-I and the IGF binding proteins (IGFBP-1, 2 and 3) decreases with age in healthy adults and is increased in acromegalic patients

OBJECTIVE Several in-vitro studies have suggested that the biological actions of IGF-I can be modified by the presence of specific IGF binding proteins. In man, the 24-hour serum levels of IGF-I and IGFBP-3 remain constant, but short-term changes in the IGF-l/IGFBP-3 ratio have been described following GH administration. Serum levels of IGF-I and IGFBP-3 decrease with age in normal adults and are elevated In active acromegaly due to excessive GH secretion. However, the Individual ratios between serum levels of IGF-I and IGFBP-3 in acromegalic and healthy adults have not been described previously. METHODS AND MATERIALS We studied this ratio In 198 healthy adults and In 56 acromegalic patients, grouped according to their serum GH levels (group I GH < 2mLU/l II GH 2–10mLU/l; III GH > 10mLU/l). In all subjects a single blood sample was drawn for IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3 and GH measurements by specific RIAs. In 38 of the patients a 24-hour urinary collection was performed for GH determination. RESULTS In healthy adults serum levels of IGF-I and IGFBP-3 decreased with Increasing age (r =?0.52 and r=?0.34, respectively, P< 0.0001). In addition, the molar IGF-l/IGFBP-3 ratio declined with increasing age (r =?0.44, P – 0.0001). In patients with acromegaly and high serum GH levels (group III), circulating IGF-I was increased 7–97 standard deviations (SDS) and IGFBP-3 was increased 4.20 SOS (P < 0.0001). Serum levels of IGF-II were normal in all three groups (588 ± 240μ/l) whereas IGFBP-1 and IGFBP-2 levels were low and IGFBP-2 levels decreased significantly with increasing serum GH levels (P < 0.0001). The molar IGF-l/IGFBP-3 ratio in the acromegalic patients was significantly higher than in the controls (P < 0.0001) and correlated significantly with urinary GH excretion (r = 0.67, P < 0.0001) as well as with serum GH levels (r = 0.73, P < 0.0001). CONCLUSION We demonstrated a decreasing molar IGF-l/IGFBP-3 ratio with increasing age in healthy adults and an increased ratio between serum IGF-I and IGFBP-3 levels in acromegalic patients. As IGF-II is normal and IGFBP-1 and IGFBP-2 are inversely correlated to the serum GH levels In the acromegalic patients, we speculate that the molar ratio between IGF-I and IGFBP-3 reflects free (biologically active) IGF-I and Is dependent on GH levels.     

Normal growth despite GH, IGF-I and IGF-II deficiency.

A 6.5-year-old male with normal linear growth, despite septo-optic dysplasia, panhypopituitarism and a deficient GH/IGF axis, is presented. In addition to measuring IGF-I, IGF-II and IGFBP-3, serum IGFBP-1, -2, -4 and -5 were measured. A human osteosarcoma cell line was used to assess growth-promoting activity in the patient's serum. The role of leptin in linear growth in this case was investigated. There was no evidence for hyperinsulinism or hyperandrogenism. GH was undetectable upon multiple stimulation. GHBP was elevated. Serum IGF-I (25 microg/l), IGF-II (194 microg/l), IGFBP-3 (0.4 mg/l), and IGFBP-5 (87 microg/l) levels were low compared to age-matched prepubertal children. Serum IGFBP-4 level was normal. Molecular size of IGF-II in the patient's serum was normal, suggesting normal IGF-II bioavailability. Human osteosarcoma cell proliferation in response to the patient's serum was similar to sera from age-matched normal controls. Leptin levels were markedly elevated. Osteoblast cell proliferation was not stimulated by leptin. The data demonstrate that normal growth and osteoblast cell proliferation in this patient is not mediated by GH, total IGFs, insulin, or leptin, and suggest the presence of a yet unidentified growth factor or mechanism. The case offers a detailed picture of binding proteins in a case of growth without GH. It introduces osteoblast cell proliferation as a method of assessing serum growth-promoting activity in such cases. It adds IGF-II and leptin to the list of excluded growth-promoting candidates in GH-independent growth, and further demonstrates our incomplete understanding of the phenomenon of growth.     

Effects of recombinant human insulin-like growth factor I administration on spontaneous and growth hormone (GH)-releasing hormone-stimulated GH secretion in anorexia nervosa

Exaggerated GH and reduced insulin-like growth factor I (IGF-I) levels are common features in anorexia nervosa (AN). A reduction of the negative IGF-I feedback could account, in part, for GH hypersecretion. To ascertain this, we studied the effects of recombinant human (rh)IGF-I on spontaneous and GH-releasing hormone (GHRH)-stimulated GH secretion in nine women with AN [body mass index, 14.1 +/- 0.6 kg/m2] and in weight matched controls (normal weight). Mean basal GH concentrations (mGHc) and GHRH (2.0 microg/kg, iv) stimulation were significantly higher in AN. rhIGF-I administration (20 microg/kg, sc) significantly reduced mGHc in AN (P < 0.01), but not normal weight, and inhibited peak GH response to GHRH in both groups; mGHc and peak GH, however, persisted at a significantly higher level in AN. Insulin, glucose, and IGFBP-1 basal levels were similar in both groups. rhIGF-I inhibited insulin in AN, whereas glucose remained unaffected in both groups. IGFBP-1 increased in both groups (P < 0.05), with significantly higher levels in AN. IGFBP-3 was under basal conditions at a lower level in AN (P < 0.05) and remained unaffected by rhIGF-I. This study demonstrates that a low rhIGF-I dose inhibits, but does not normalize, spontaneous and GHRH-stimulated GH secretion in AN, pointing also to the existence of a defective hypothalamic control of GH release. Moreover, the increased IGFBP-1 levels might curtail the negative IGF-I feedback in AN.     

Growth hormone (GH) replacement in GH-deficient adults: a crossover trial comparing the effect on metabolic control, well-being and compliance of three injections per week versus daily injections

Growth hormone (GH) replacement therapy regimens in adults using daily subcutaneous (sc) injections may not be optimal with respect to carbohydrate and lipid metabolism. The aim of this study was to compare the efficacy of three times weekly injections with daily sc GH injections in terms of serum IGF-I, IGFBPs, lipoprotein levels, serum bone markers, glucose metabolism, body composition, compliance and well-being.Twenty hypopituitary men, 46–76 years, on a course of stable conventional GH replacement therapy for more than 12 months, were included in a 16-week crossover trial. During the first 8 weeks GH was administered three times per week followed by 8 weeks with daily sc injections with the same weekly dose of GH. Fasting serum samples were collected at baseline and on two consecutive days at the end of each 8-week period.Serum IGF-I and IGFBP-3 concentrations were lower both the first and second morning after the last injection during the period with three injections per week. The second morning after the last GH injection in this period the IGF-I/BP-3 ratio, plasma insulin and FFA were lower whereas IGFBP-1 was increased as compared with values obtained during the period with daily injections. Serum Lp(a) levels, body composition, fat distribution, well-being and compliance were not differently affected by the two treatment regimens.These results suggest that the same weekly dose of GH given as three injections per week reduces serum IGF-I and IGFBP-3 levels without affecting Lp(a) levels. The day-to-day variation in glucose metabolism and FFA serum levels differs considerably between the two modes of GH administration.     

Free and total insulin-like growth factor (IGF)-I, -II,and IGF binding protein-1, -2, and -3 serum levels in patients with active thyroid eye disease

To determine whether serum levels of total (T) and free (F) IGF-I and -II and IGF binding protein (IGFBP),-1, -2, and -3 are normal in euthyroid patients with Graves' disease and active thyroid ophthalmopathy, we investigated the above-mentioned parameters in 21 patients (11 male, 10 female) aged 50.8 +/- 11.8 yr (range 35-70) and 19 healthy individuals matched for age, gender, and body mass index. All patients had active thyroid eye disease (TED) with clinical activity scores > or = 4 and positive orbital octreoscan in both eyes. Serum T and F IGF-I and IGF-II were determined using noncompetitive time-resolved monoclonal immunofluorometric assays, IGFBP-1 was determined by an in-house RIA, IGFBP-2 by a novel in-house time-resolved immunofluorometric assay, whereas IGFBP-3 by an immunoradiometric assay. All data are expressed as mean +/- SD. Our results show that T and F IGF-I, -II, and IGFBP-1, -2, and -3 levels in patients were similar to controls and did not show any significant difference. Specifically, mean T IGF-I for patients group was 131 (61), F IGF-I was 0.47 (0.16), T IGF-II was 1056 (300), F IGF-II was 1.45 (0.54), IGFBP-1 was 33 (14), IGFBP-2 was 848 (377), and finally IGFBP-3 was 3953 (1422). For controls, mean T IGF-I was 146 (51), F IGF-I was 0.85 (0.43), T IGF-II was 939 (197), F IGF-II was 1.53 (0.53), IGFBP-1 was 44 (24), IGFBP-2 was 764 (316) and finally IGFBP-3 was 3721 (1017). Furthermore, no statistically differences emerged in the ratio between molar weights of T IGF-I/IGFBP-3 and T IGF-II/IGFBP-3, as well as to the F/T IGF-I and F/T IGF-II. Finally, no relationship was found between the levels of the above-mentioned parameters and clinical activity scores, octreoscan scores, and thyroid hormones. Our data demonstrate for the first time that serum levels of IGFs (including free fractions) and IGFBPs are not increased in euthyroid Graves' patients with active TED. The increased IGF levels in retrobulbar tissues previously described, appear to be independent of serum IGFs concentration and probably represent autocrine and/or paracrine activity.     

Long-term effects of insulin-like growth factor (IGF)-I treatment on serum IGFs and IGF binding proteins in adolescent patients with growth hormone receptor deficiency

OBJECTIVE The aim of this investigation was to study the effect of relatively high dose IGF-I therapy given for several months, on serum levels of IGF-I, IGF-II and IGFBP-3, and on IGF-I pharmacokinetics In patients with growth hormone insensitivity due to GH receptor dysfunction. DESIGN AND PATIENTS Two adolescent subjects from Ecuador were treated with recombinant IGF-I at a dosage of 120μg/kg s.c. twice dally, in combination with a GnRH analogue for 8 months. MEASUREMENTS Serum was sampled at baseline and at 3–8 months, for determination of IGF-I, IGF-II and IGFBP-3 by radioimmunoassay, and for evaluation of IGFBPs and IGFBP-3 protease activity by Western ligand blot and protease assay, respectively. RESULTS Peak serum IGF-I levels ranged from 272 to 492μg/l. Mean serum IGF-II levels were decreased concurrently with the increase in IGF-I. Serum IGFBP-3 levels failed to rise with prolonged IGF-I treatment. There was no apparent change In the half-life of IGF-I during the treatment period. CONCLUSIONS IGF-I administration does not increase serum levels of IGFBP-3 or significantly alter IGF-I pharmacokinetics.