Insulin-like growth factors and insulin: comparative aspects

A high linear growth is associated with an increased risk of childhood diabetes mellitus

Insulin release and growth are intimately connected. The aim of the present study was to investigate height and weight in diabetic children from birth to onset of Type 1 (insulin-dependent) diabetes mellitus compared to that in referent children. Data on height and weight were collected from mailed questionnaires and from growth records obtained from the child health clinics and schools in 337 recent-onset diabetic children, 0-14 years old, and from 517 age-, sex-, and geographically matched referent children. A total of 9002 paired height and weight observations were collected. The anthropometric development of the children was expressed as standard deviation scores using the National Center for Health Statistics/Centers for Disease Control (NCHS/CDC) growth reference material. On the average, the diabetic children were consistently taller than the referent children, a finding more pronounced among the boys. The diabetic boys were significantly taller from 7 to 1 years before the clinical onset of the disease, regardless of age at onset. A similar tendency was found for the girls. When mean height from 5 to 1 years before onset was used as a possible risk factor for diabetes, a linearly increasing trend in the odds ratio was found for diabetes in boys (odds ratio = 1.0; 1.57; 2.46 for height standard deviation score values less than 0; 0-1 and greater than 1, respectively; p = 0.002 for trend). A similar, but statistically not significant, tendency was found for girls (odds ratio = 1.0; 1.44; 1.43). As regards height increment from birth similar trends in odds ratios were found.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of coho salmon growth by insulin-like growth factor I

The effect of insulin-like growth factor I on growth rate of coho salmon (Oncorhynchus kisutch) was examined. Juvenile coho salmon received implants of osmotic minipumps containing recombinant bovine insulin-like growth factor I (rbIGF-I) or saline for a period of 3 to 4 weeks. High doses of rbIGF-I (greater than 0.13 microgram.g-1.d-1) resulted in hypoglycemia and death. In 2-year-old coho salmon, 0.09 microgram.g-1.d-1 rbIGF-I administered for 25 days doubled linear growth rate and increased growth rate in weight by 40%. In rapidly growing, 1-year-old coho salmon, growth rate was not altered by rbIGF-I at 0.01 or 0.05 micrograms.g-1.d-1 for 31 days. In ration-limited fish exhibiting slow growth in the control group, rbIGF-I (0.02 microgram.g-1.d-1) increased linear growth rate by up to threefold and growth rate in weight by up to fourfold. The results indicate that exogenous treatment with mammalian IGF-I can stimulate coho salmon growth under some conditions, and that endogenous IGF-I may be an important factor in regulating growth of teleosts.

Modulation of glomerular proteoglycans by insulin-like growth factor-1

Effect of insulin-like growth factor-1 (IGF) on the synthesis of glomerular proteoglycans (PGs) in an ex vivo recirculating organ perfusion system was investigated. Kidneys were perfused with a medium (approximately 80 ml) containing [35S]-sulfate (250 microCi/ml) and IGF (62.5 to 625 ng/ml). After radiolabeling, a small cortical piece was saved for tissue autoradiography, and the remaining kidney and the perfusion medium were utilized for biochemical studies. The glomeruli were isolated; their PGs extracted and characterized. A two- to threefold increase of the total radioactivities in tissue and media fractions was observed with the exposure to IGF. By Sepharose CL-6B chromatography, the tissue PGs eluted as two peaks (A and B) with Kav = 0.24 and 0.48, and the majority of the radioactivity was confined to peak A. This peak contained intact PGs while peak B included glycosaminoglycan (GAG) chains. Elution profiles of the glomerular PGs were similar in the control and IGF groups. However, there was a disproportionate increase of chondroitin/dermatan sulfate in the IGF group. The media fractions also had two peaks, and most of the radioactivity was associated with peak B containing GAG chains. A remarkable accentuation of peak B along with significant increase in the chondroitin/dermatan sulfate were observed in the IGF group. By DEAE-Sephacel chromatography, the PGs/GAGs of IGF group eluted at a relatively lower salt concentration as compared to the control. Autoradiography revealed a relatively high concentration of radioactivity over the mesangium as compared to the other cell types of the glomerulus. [35S]-methionine studies revealed a generalized increase of protein synthesis in the IGF group, but comparatively much less than that of PGs/GAGs. These results indicate that IGF enhances the biosynthesis of PGs/GAGs by various cell types of the renal glomerulus, especially that of the mesangial cell, as reflected by the selective increase of chondroitin/dermatan sulfate.

Hormonal control of sulfate uptake by branchial cartilage of coho salmon: role of IGF-I

The direct hormonal control of sulfate uptake by cartilage matrix of coho salmon was examined by exposing branchial cartilage to 1 microCi.ml-1 35SO4 for 48 hours at 15 degrees C in a defined medium. Sulfate uptake occurred primarily in cartilage (rather than bone) and the amount of specific uptake was similar in epibranchial and ceratobranchial cartilages. Intact and hypophysectomized coho salmon starved for 22 days had equivalent in vitro sulfate uptake, which in both cases were 30% of the uptake seen in branchial cartilage of fed, intact controls. In branchial cartilage from starved coho salmon, in vitro exposure to recombinant bovine insulin-like growth factor I (rbIGF-I) at 1, 10, 100, and 1,000 ng.ml-1 caused a dose-dependent increase in sulfate uptake, with a maximum 3-fold increase over control at 1,000 ng.ml-1 rbIGF-I. Coho salmon insulin (1, 10, 100, and 1,000 ng.ml-1) resulted in a maximum 30% increase in sulfate uptake at the highest dose. Growth hormone and triiodo-L-thyronine had no direct effect on in vitro sulfate uptake. The results indicate that IGF-I has direct effects on coho salmon cartilage and may be an important regulator of growth in salmon and other teleosts.

Purification and sequencing of molluscan insulin-related peptide I (MIP I) from the neuroendocrine light green cells of Lymnaea stagnalis

The body growth controlling cerebral neuroendocrine light green cells of the freshwater snail, Lymnaea stagnalis, express various members of a gene family encoding different though related prepromolluscan insulin-related peptides. In the present study, molluscan insulin-related peptide I (MIP I) together with the corresponding connecting peptide, C alpha peptide, have been isolated and structurally identified. MIP I is a heterodimer of A and B chains bonded by disulphide bridges. Two isoforms of MIP I could be discerned. Mass spectrometry revealed that of one form both the A and B chains have N-terminal pyroglutamyl residues, whereas of the other form only the B chain has such residues. After removal of the pyroglutamyl residues with pyroglutamate aminopeptidase, followed by disulphide bond cleavage and pyridylethylation of cysteine residues, the sequences of MIP I have been determined using Edman degradation as: A chain: (p)QGTTNIVCECCMKPCTLSELRQYCP; B chain: pQPSACNINDRPHRRGVCGSALADLVDPACSSSNGPA. The C alpha peptide has also been isolated and its sequence was determined as NAETDLDDPLRNIKLSSESALTYLY. These sequences are in agreement with those predicted by a cDNA sequence encoding preproMIP I, with the exception that the two C-terminal amino acids of the B chain are posttranslationally removed.

Isolation and chemical characterization of a novel insulin-related neuropeptide from the freshwater snail, Lymnaea stagnalis

A novel molluscan insulin-related peptide (MIP) III, has been isolated from alcohol extracts of the neurohaemal area of the cerebral neuroendocrine light-green neurones of Lymnaea stagnalis. MIP III was purified by sequential high-performance gel-permeation chromatography followed by reverse-phase HPLC. MIP III is a heterodimer connected by disulphide bonds. Edman degradation analysis and subsequent alignment with the A and B chains of the previously identified MIP I and II showed that the 24-amino-acid peptide with the sequence pQSRPSIVC(E)CCFNQCTVQ(E)LLAYC represents the MIP III A chain, and the 37-amino-acid peptide sequence TTQHTCSILSRPHPRGLCGSTLANMVQWLCSTYTTSS the B chain. The overall amino acid sequence of MIP III shows about 50% similarity with those of MIP I and II, and only 20-40% similarity with other peptides of the insulin superfamily. Important structural features, e.g. disulphide bridges and the hydrophobic core, are conserved in MIP III.

Insulin-like growth factor-1 stimulates growth of mouse preimplantation embryos in vitro

Because recent studies have particularly implicated the insulin growth factor family in early development, the effects of insulin-like growth factor (IGF-1) on the development of mouse embryos in vitro were investigated in detail. When added to the medium for culture of two-cell embryos, IGF-1 stimulated the number of cells in the resultant blastocysts after 54 hr, entirely by increasing the number of cells in the inner cell mass (ICM) (16.0 +/- 0.5 vs. 12.6 +/- 0.5 cells/ICM). This stimulation was also achieved when ICMs were isolated from blastocysts prior to culture for 24 hr with IGF-1 (22.3 +/- 1.0 vs. 17.5 +/- 0.8 cells/ICM). There was no effect on IGF-1 on trophectoderm (TE) cell proliferation. In morphology studies, IGF-1 also increased the proportion of blastocysts (62% +/- 3% vs. 49% +/- 4%) while decreasing the number of embryos remaining as morulae (32% +/- 3% vs. 38% +/- 2%) or in the early cleavage stages (7% +/- 3% vs. 13% +/- 3%) after 54 hr culture from the two-cell stage. All these effects were achieved with EC50s of approximately 60 pM IGF-1, which is in the range for IGF-1 receptor mediation; however, cross reaction with insulin, IGF-2, or other unknown receptors is not excluded. Nonetheless, the results show that physiological concentrations of IGF-1 (17-170 pM, 0.1-1 ng/ml), which have been observed in the reproductive tract, affect the early embryo, suggesting a normal role for this factor in the regulation of growth of the developing conceptus before implantation.

Metabolic actions of insulin-like growth factor II in cultured adult rat hepatocytes are not mediated through the insulin-like growth factor II receptor

Short- and long-term regulation of hepatic carbohydrate metabolism by insulin-like growth factor II was studied in primary cultures of adult rat hepatocytes and compared to the metabolic potency of insulin. Insulin-like growth factor II stimulated glycogen synthesis from [14C]glucose, uptake of [3H]aminoisobutyric acid and [14C]lactate formation from [14C]glucose up to three-fold. Basal glycogenolysis was inhibited to about 10%, and glucagon-activated glycogenolysis was blocked completely. The enzymatic activity of glucokinase and pyruvate kinase was induced two-fold, the glucagon-dependent induction of phosphoenolpyruvate carboxykinase was antagonized. Compared to insulin, half-maximal responses required up to 50 times higher insulin-like growth factor II concentrations ranging from 10-20 nmol/l. A similar difference was observed for binding affinity of insulin-like growth factor II to the insulin receptor. The interaction with the insulin-like growth factor II/mannose 6-phosphate (IGF-II/Man-6-P) receptor was examined by studying 125I-insulin-like growth factor II binding and uptake of lysosomal enzymes. The affinity of insulin-like growth factor II to the IGF-II/Man-6-P receptor was considerably higher than for the insulin receptor. Antibodies against the IGF-II/Man-6-P receptor did not affect metabolic responses to insulin-like growth factor II, while binding to its receptor and the receptor-mediated endocytosis of arylsulphatase A were strongly inhibited. Thus, in adult rat liver insulin-like growth factor II appeared to exert metabolic actions not via interaction with its own receptor but through low affinity binding to hepatic insulin receptors.

Growth and subsequent lactation in primigravid Holstein heifers after prepartum bovine somatotropin treatment

Thirty-seven primigravid Holstein heifers (600.7 +/- 9.4 kg) were used to determine the effect of recombinant bST, administered during the last trimester of gestation, on growth and subsequent 270-d milk yield. Treatments consisted of daily subcutaneous injections of saline or of 20 or 40 mg of recombinant bST. Four weeks before expected date of parturition, 8 heifers (3 receiving saline, 3 receiving 20 mg of bST, and 2 receiving 40 mg of bST) were fitted with jugular catheters, and blood plasma bST and insulin-like growth factor-I concentrations were determined in samples collected during a 9-h period. Feed efficiency (DMI/gain) was improved in heifers treated with 20 mg of bST, but DMI was not affected by treatment. Average daily gain was increased in heifers treated with 20 mg of bST, but not in those treated with 40 mg of bST. Fat-uncorrected milk yield following prepartum bST treatment was 19% higher in heifers treated with 20 mg of bST, but the 40-mg dose of bST did not increase milk yield. Percentage of milk fat was lower in heifers treated with 20 mg of bST prepartum, but daily milk fat yields did not differ among groups. Solids-not-fat yield was highest in the group treated previously with 20 mg of bST. The higher milk yield of these heifers became significant (P less than .05) only after 90 d of lactation. Plasma bST and insulin-like growth factor-I concentrations were both elevated in bST-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptides related to insulin-like growth factor 1 in the gastro-entero-pancreatic system of bony and cartilaginous fish

Evidence for the presence of peptides, related to insulin-like growth factor 1 (IGF-1) has been obtained in serum and various organs of representatives of osteichthyes and chondrichthyes, i.e., the bony fish Myoxocephalus (Cottus) scorpius and the cartilaginous fish Raja clavata. The peptides were identified by means of gel chromatography and an IGF-1 radioimmunoassay. IGF-1-like immunoreactivity was detected in three different apparent molecular mass forms, i.e., 17 kDa, 6 kDa and 4 kDa, the occurrence of which seemed to depend on the species. When the same antiserum was used immunohistochemically, IGF-1-like immunoreactivity was observed in endocrine cells of the open type in the intestinal mucosal epithelium. These cells exhibited distinct and species-specific distribution patterns. Endocrine cells of the pancreas as well as epithelial cells of the pancreatic duct also showed IGF-1-like immunoreactivity. Occasionally, IGF-1-like immunoreactivity was observed also in interstitial cells. The distribution patterns and densities of the IGF-like immunoreactive cells correlated with the results obtained by radioimmunoassay of the crude extracts. Absorption studies indicated that the IGF-1-like peptides observed differ from mammalian and submammalian insulins as well as from mammalian IGF-1.

Growth hormone stimulates cortical bone formation in immature hypophysectomized rats

Daily subcutaneous injections of rat derived growth hormone to immature, hypophysectomized rats stimulated significant increases in body weight gain, serum osteocalcin, skeletal alkaline phosphatase and incorporation of radioactive thymidine and proline into the compact bone of femurs and tibiae. Equimolar doses of insulin-like growth factor-II did not produce similar biological effects. The data support the contention that growth hormone at equimolar concentration is a stronger osteogenic agent than is insulin-like growth factor-II in vivo.

The circulating molecular weight forms of infused recombinant insulin-like growth factor-I and effects on glucose and fat metabolism in lambs

We have investigated the relationship between the plasma distribution of infused recombinant insulin-like growth factor-I across the insulin-like growth factor binding proteins and the resultant effects on glucose and fat metabolism. The studies were performed in 24-h fasted ram lambs which received primed constant infusions of 3H labelled glucose tracer. When isotopic equilibrium had been reached, the animals received 90-min infusions of human insulin-like growth factor-I at various doses (2.5, 20, 40 and 120 micrograms.kg-1.h-1, n = 3 for each dose). Total plasma insulin-like growth factor-I was significantly elevated by infusion at a rate of 40 micrograms.kg-1.h-1 (from 185 +/- 14 micrograms/l to 442 +/- 41 micrograms/l, p less than 0.05) and 120 micrograms.kg-1.h-1 (from 181 +/- 2 micrograms/l to 953 +/- 39 micrograms/l, p less than 0.005). The plasma concentrations of insulin-like growth factor-I not associated with binding proteins remained undetectable (less than 15 micrograms/l) at the end of the 2.5 and 20 micrograms.kg-1.h-1 doses, but were significantly elevated at the end of the 40 and 120 micrograms.kg-1.h-1 infusions (to 71 +/- 14 micrograms/l, p less than 0.05 and 176 +/- 55 micrograms/l, p less than 0.01 respectively). The infused insulin-like growth factor-I associated primarily with 35-60 kilodalton binding proteins. Glucose kinetics were significantly altered only by the highest dose infusion, during which there was a fall in plasma glucose concentration from 3.5 +/- 0.2 mmol/l to 1.9 +/- 0.2 mmol/l (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant human insulin-like growth factor I (rhIGF I) reduces hyperglycaemia in patients with extreme insulin resistance

The syndrome of type A insulin resistance is encountered in young women and is characterized by glucose intolerance or frank diabetes mellitus, endogenous hyperinsulinism, insensitivity to insulin administration, acanthosis nigricans and virilization. The insulin resistance is due to reduced cellular insulin binding because of a lack of or defective binding sites and/or because the interaction with the tyrosine kinase of the beta-subunit is hindered. This study was undertaken to find out whether hyperglycaemia in these patients may be influenced by the administration of recombinant human insulin-like growth factor I which exerts insulin-like effects through the insulin receptor as well as the type 1 insulin-like growth factor I receptor. Recombinant human insulin-like growth factor I was intravenously administered in two subsequent doses of 100 micrograms/kg body weight to three women with type A insulin resistance. An immediate but slow fall of blood glucose was observed. The glucose disappearance rate was 28.0 mumol/min, i.e. considerably lower than that seen in healthy subjects. The markedly elevated insulin and C-peptide levels fell in a parallel manner to blood glucose but not to normal levels. The results show that recombinant human insulin-like growth factor I, presumably by reacting with the type 1 insulin-like growth factor receptor, can normalize serum glucose levels in patients with severe insulin resistance at least for several hours. We suggest that the potential or recombinant human insulin-like growth factor I to control hyperglycaemia in type A insulin resistant patients should be explored in more depth.

The effects of infusion of insulinlike growth factor (IGF) I, IGF-II, and insulin on glucose and protein metabolism in fasted lambs

In vivo effects of 300-min infusions of recombinant insulinlike growth factor I (IGF-I) and IGF-II on glucose and protein metabolism have been investigated in awake, fasted lambs. Two doses of recombinant human (rh) IGF-I were infused: 6.7 nmol/kg.h, which induced hypoglycemia, and 2.0 nmol/kg.h, which did not. The effects were compared with an insulin infusion (0.17 nmol/kg.h) that had the same hypoglycemic potential as the high dose rhIGF-I infusion. rhIGF-II was infused at a rate of 6.7 nmol/kg.h. Primed constant infusions of isotopically labeled glucose, urea and leucine tracers were used to determine glucose and protein kinetics. rhIGF-I lowered blood glucose by increasing the rate of glucose clearance (P less than 0.01), in contrast to insulin, which both increased clearance and reduced glucose production. Net protein loss was reduced after infusion of low and high dose rhIGF-I and insulin by 11% (P less than 0.05), 15% (P less than 0.01), and 12% (P less than 0.05), respectively. rhIGF-II infusion did not alter the rate of net protein loss. In contrast to insulin, high dose rhIGF-I infusion increased the rate of protein synthesis in skeletal (P less than 0.05) and cardiac muscle (P less than 0.01) and in hepatic tissue (P less than 0.05). We conclude that (a) protein metabolism is more sensitive than glucose metabolism to rhIGF-I infusion, as protein loss was reduced by an rhIGF-I infusion that did not alter glucose kinetics; (b) protein synthesis is increased by rhIGF-I infusion but not by insulin infusion; and (c) rhIGF-II is a less effective anabolic agent than rhIGF-I. We speculate that the effects of rhIGF-I on protein metabolism are not mediated by insulin receptors.

Presence of IGF-1-like peptides in the neuroendocrine system of the Atlantic hagfish, Myxine glutinosa (Cyclostomata): evidence derived by chromatography, radioimmunoassay and immunohistochemistry

By the use of radioimmunoassay and chromatography peptides related to insulin-like growth factor 1 (IGF-1) have been identified in the cylostomian species Myxine glutinosa. IGF-1-like-immunoreactivity was detected in serum as well as in brain, intestine, pancreas and liver. After acid gel chromatography, the IGF-1-like immunoreactivity eluted as one major peak, with an apparent molecular weight of between 2-4 kDa. When the same antiserum was applied immunohistochemically, IGF-1-like-immunoreactivity was observed in endocrine cells of the mucosal epithelium throughout the primitive intestinal tube. These cells were of the open type and occurred in small clusters. In addition, the majority of the endocrine cells of the pancreas of Myxine displayed IGF-1-like-immunoreactivity. In some of the specimens investigated IGF-1-like-immunoreactive perikarya and fibers were observed on all levels of the brain. Distribution patterns and densities of the IGF-1-like-immunoreactive structures in Myxine correlated with the measurements obtained by radioimmunoassay. Absorption studies with insulin- and IGF-related peptides as well as with crude extracts and the peak material obtained after gel chromatography indicated that the IGF-1-like peptides in Myxine are different from mammalian and non-mammalian insulins as well as from mammalian IGF-1. Generally, the results suggest a long phylogenetic history of IGF-1-like peptides and indicate their fundamental functional impact in all vertebrates.

Mouse blastocysts respond metabolically to short-term stimulation by insulin and IGF-1 through the insulin receptor

Insulin specifically stimulates protein synthesis in compacted mouse embryos on days 3 and 4 after fertilization, with an EC50 of 0.5 pM (Harvey and Kaye, 1988). The identity of the receptor mediating this short-term effect of insulin was further examined by dose-response studies with IFG-1 and by using a specific anti-insulin receptor antiserum that has no appreciable cross-reaction with IGF-1 receptors. IGF-1 caused a maximum 40% stimulation of protein synthesis after 4 h exposure (similar to the response to insulin) with an EC50 of 150 pM IGF-1. The insulin receptor-specific antiserum, or IgGs isolated from it, also stimulated protein synthesis at dilutions as high as 1:1,000 to the same degree as insulin (approximately 40%). This agonistic action of the insulin receptor antiserum, the EC50 of 150 pM for IGF-1, and the previously established EC50 of 0.5 pM for insulin, all with similar maximal stimulation, strongly support the conclusion that the short-term metabolic stimulation of mouse blastocysts by insulin is mediated by insulin receptors. Immunosurgical isolation of inner cell masses before and after exposure to 1.7 pM insulin (sufficient to stimulate only the insulin receptor) showed that insulin stimulates protein synthesis in these cells as well as in the trophectoderm cells of the blastocyst. This finding suggests that in intact blastocysts, insulin may travel across the trophectoderm to the inner cell mass, acting anabolically on both tissues. Analysis of the agonistic effect of the B-10 antiserum showed there was no evidence of an unresponsive subpopulation of embryos.

In vivo metabolic action of insulin-like growth factor I in adult rats

The acute metabolic actions of insulin-like growth factor I were studied in anaesthetized adult rats and its potency was compared to that of insulin. Following an i.v. bolus injection of insulin-like growth factor I a dose-dependent decrease of blood glucose and serum non-esterified fatty acid concentrations was noted with a potency of about 2% that of insulin. Stimulation of total body glucose disposal during euglycaemic clamping required approximately 50 times higher insulin-like growth factor I serum concentrations to achieve an identical half-maximal response. A similar difference in potency was observed for the stimulatory action on 2-deoxyglucose uptake and on glycogen formation in skeletal muscle. Lipogenesis in epididymal fat pads was increased dose-dependently by both hormones requiring approximately 30 times higher half-maximally effective serum concentrations of insulin-like growth factor I. These data demonstrate that insulin-like growth factor I exerted acute insulin-like metabolic actions in vivo with low potency. These effects were probably mediated via insulin receptors. A preferential stimulation of glucose metabolism in skeletal muscle was not observed.

Solitary fibrous tumor of the pleura. An immunohistochemical, electron microscopic and tissue culture study of a tumor producing insulin-like growth factor I in a patient with hypoglycemia

We report a patient with recurrent hypoglycemia most likely caused by a solitary fibrous tumor of the pleura. After removal of the tumor, hypoglycemia resolved. The bland histologic picture of this tumor is emphasized. Electron microscopic and immunohistochemical observations support its non-mesothelial derivation. In vitro studies demonstrated that the tumor tissue produced insulin-like growth factor I (IGF-I), and its role as the cause of hypoglycemia is discussed.

Secretion of insulin-like growth factor I and its binding proteins by collecting duct cells

Insulin-like growth factor I (IGF-I) has been found in the kidney, particularly in the collecting duct in the rat. Since cultured rabbit collecting duct cells constitute a convenient system for in vitro studies, we have examined whether these cells secrete IGF-I. Culture medium conditioned by collecting duct cells was concentrated by reverse phase chromatography and applied to a Sephadex G100 column equilibrated in a denaturing buffer. Two major species with apparent molecular weights of 7.5 and greater than 25 kilodaltons (kD) were identified by IGF-I RIA. A smaller amount of 10 kD species was also observed. Further characterization of 7.5 kD IGF-I immunoreactive species by reverse phase HPLC showed that it eluted in a single peak. To determine whether the higher molecular weight species possessed IGF-I binding activity, appropriate fractions were desalted, incubated with [125I]IGF-I (thr59) for two hours at 30 degrees C and applied to a Sephadex G100 column equilibrated in a non-dissociating buffer. The major peak of radioactivity was confined to a high molecular weight region; there was no radioactivity in the fractions corresponding to 7.5 kD. Western ligand analysis of unreduced conditioned medium identified two IGF-I binding species of 25 and 30 kD, similar in size to species observed in normal rabbit serum. 125I-IGF-I binding as assessed in a charcoal adsorption assay could be displaced by IGF-I and IGF-II but not by insulin. Further characterization of the 10 kD peak of IGF-I immunoreactivity indicated that it did not possess IGF-I binding activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Evolution of the insulin superfamily: cloning of a hybrid insulin/insulin-like growth factor cDNA from amphioxus

Although insulin and the insulin-like growth factors (IGFs) share marked similarities in amino acid sequence and biological activity, their evolutionary origins have not been resolved. To investigate this issue, we recently cloned a cDNA encoding an insulin-like peptide (ILP) from a primitive chordate species, amphioxus (Branchiostoma californiensis). The deduced sequence of amphioxus preproILP indicates that it is a hybrid molecule containing features characteristic of both insulin and IGF. Like proinsulin, amphioxus proILP contains a C-peptide, which is flanked by paired basic residues and is probably removed by proteolysis. However, proILP also contains an extended carboxyl-terminal peptide region that can be divided into D and E domains similar to those of proIGF. Sequence comparisons show that the amphioxus ILP A and B domains are equally homologous to those of human insulin and IGF-I and -II. Based on these results and the exon-intron organization of the amphioxus ILP gene, we propose that IGF emerged at a very early stage in vertebrate evolution from an ancestral insulin-type gene.

Insulin-like growth factor I (IGF-I) distribution in the tissue and extracellular compartment in different regions of rat brain

The regional distribution of insulin-like growth factor I (IGF-I) was examined in the tissue and extracellular compartment of rat brain. The tissue content of IGF-I was the highest in the pituitary gland, followed by the olfactory bulb, upper brainstem, cerebellum, striatum, hippocampus, lower brainstem, and cerebral cortex. The extracellular concentration was studied by intracerebral microdialysis technique, and the highest content was found in the hippocampus, followed by the olfactory bulb, hypothalamus, cerebellum, striatum, and cerebral cortex. The tissue and extracellular contents were significantly correlated in the olfactory bulb, hypothalamus, cerebellum, striatum, and cerebral cortex. IGF-I might act by paracrine and/or autocrine regulatory mechanisms in these regions.

Metabolic actions of insulin-like growth factor-I in cultured hepatocytes from adult rats

Short-term and long-term regulation of hepatic carbohydrate metabolism by insulinlike growth factor-I was studied in primary cultures of adult rat hepatocytes and compared with the metabolic potency of insulin. Insulinlike growth factor-I stimulated the formation of [14C]lactate from [14C]glucose up to three-fold with a half-maximally effective concentration of approximately 50 nmol/L. Basal glycogenolysis was inhibited by about 20%, and glucagon-activated glycogenolysis was blocked completely by insulinlike growth factor-I with half-maximally effective concentrations of about 1.5 to 2 nmol/L. The activity of the key glycolytic enzymes glucokinase and pyruvate kinase were induced twofold. The glucagon-dependent induction of phosphoenolpyruvate carboxykinase--the key gluconeogenic enzyme--was antagonized with a half-maximally effective concentration of about 5 nmol/L. This inhibition of the glucagon-dependent induction of the enzyme was accompanied by a similar reduction of the increase in phosphoenolpyruvate carboxykinase-mRNA level as assessed by Northern blot analysis. The potency of insulinlike growth factor-I at half-maximally effective concentrations was approximately 2% to 4% that of insulin. Because binding studies demonstrated a comparably low affinity of insulinlike growth factor-I to the insulin receptor, it is suggested that in adult liver--in contrast to fetal and regenerating liver--insulinlike growth factor-I could exert short-term and long-term metabolic effects on parenchymal cells only through interaction with the insulin receptor.

Direct effect of insulin and insulin-like growth factor-I on the secretory activity of rat pancreatic beta cells

Purified pancreatic Beta cells were labelled with 3H-tyrosine before studying their secretory activity in perifusion. At 1.4 mmol/l glucose, the cells released similar fractions (0.01% per min) of their contents in preformed and in newly formed insulin. At 20 mmol/l glucose plus 10(-8) mol/l glucagon, these fractional release rates increased by 16 and 40-fold respectively. The preferential release of newly synthesized as compared to stored insulin is attributable to a heterogeneity in individual cell responses. The secretory responsiveness to glucose plus glucagon was completely suppressed by 10(-7) mol/l clonidine. Insulin induced a 20% reduction at 10(-6) mol/l, but remained without effect at 10(-7) mol/l. Insulin-like growth factor-I provoked a 30% decrease at 5.10(-9) mol/l. It is concluded that the type-I insulin-like growth factor receptors on pancreatic Beta cells mediate a suppressive action on the insulin release process. Their high affinity for insulin-like growth factor-I allows physiologic levels of this peptide to participate in the regulation of insulin release. Their low affinity for insulin provides the basis for a minor feedback action by this hormone at concentrations exceeding the normal circulating levels.

Therapeutic potential of insulinlike growth factor i

Human recombinant insulinlike growth factor I is a promising therapeutic agent for diseases characterized by relative insulin resistance, e.g., diabetes mellitus, obesity, and hypertriglyceridemia, since it suppresses growth hormone, insulin, C-peptide, and triglyceride levels and lowers the total cholesterol to high-density lipoprotein-cholesterol ratio. Moreover, insulinlike growth factor administration increases kidney function in healthy subjects (glomerular filtration rate, renal plasma flow) and may prove useful in the treatment of degenerative disorders of cartilage and bone (arthrosis, osteoporosis) as well as in catabolic states.

Effects of streptozotocin-induced diabetes mellitus on growth and hepatic insulin-like growth factor I gene expression in the rat

Poorly controlled diabetes mellitus in humans and animals is often accompanied by impaired growth. We undertook this study in young rats to determine whether the reduction in growth rate associated with streptozotocin (STZ)-induced diabetes might be related to changes in both serum insulin-like growth factor I (IGF-I) and IGF-II levels, and, if so, whether these changes reflect alterations in serum growth hormone (GH) and in hepatic IGF-I and IGF-II gene expression. Serum rat GH (rGH) levels were variable during the first 4 days after STZ administration, but during the subsequent 5- to 11-day period the mean (+/- SEM) levels in insulin-treated (DI) (21.4 +/- 4.9 ng/mL) and untreated (D) (8.5 +/- 1.5 ng/ml) diabetic rats were significantly (P less than .001) lower than in controls (C) (117.8 +/- 22.9 ng/mL). Multiple transcripts of IGF-I (7.0, 4.0, 1.9, 1.0 kb), but barely detectable amounts of IGF-II mRNA, were found in the livers of normal and diabetic rats by Northern blot analysis. Using dot blot analysis, we have shown that the abundance of total hepatic IGF-I mRNA in untreated, growth-retarded diabetic animals decreases rapidly over a period of 3 days after STZ administration. Both serum IGF-I and IGF-II levels are also diminished during this interval in these markedly hyperglycemic rats. Insulin treatment for 3 to 4 days, started either immediately (6 hours) or within 3 days after administering STZ, blunts diabetes-induced impairment of growth and restores mean hepatic IGF-I mRNA abundance to control levels, but does not normalize serum IGF-I and IGF-II concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

The E-domain peptide of rat pro-insulin-like growth factor II (proIGF-II): properties of the peptide in serum and production by rat cell lines

We previously identified a naturally occurring peptide fragment derived from the carboxyl terminal region of the E-domain of pro-insulin-like growth factor II (proIGF-II117-156) in medium conditioned by cultured BRL-3A rat liver cells. In the present study we utilized a radioimmunoassay (RIA) for this peptide to measure physiological concentrations of the peptide in media and serum. Serum levels of the E-domain peptide were very high in the 5-day neonatal rat and declined thereafter to reach low levels in adult rat serum. Chromatography of adult rat serum on Sephadex G-75 in 1 M acetic acid yielded a single broad peak of E-peptide immunoreactivity that coeluted with a synthetic E-peptide standard. However, chromatography of day 5 neonatal rat serum on Sephadex G-75 yielded two peaks of immunoreactivity. One of the peaks coeluted with a synthetic E-peptide standard, whereas the other peak eluted in a region where higher molecular weight proteins typically elute. Experiments aimed at determining whether adult rat serum contained a binding protein for the E-domain peptide revealed that: (1) serum contains little, if any, binding protein for the E-domain peptide, (2) serum contains a proteinase activity that degrades the E-domain peptide, and (3) the proteinase activity can be eliminated by acetic acid/ethanol extraction. Of several rat cell lines tested (BRL-3A, rat embryo fibroblasts (REF), hepatoma cell lines (H4, HTC), GH3 pituitary tumor cells, and normal rat kidney fibroblasts (NRK], only BRL-3A and REF cells secreted measurable E-domain peptide into the medium. In addition, it was found that some component(s) of serum could stimulate secretion of E-domain peptide from BRL-3A and REF cells. Chromatography of the immunoreactivity from BRL-3A and REF-conditioned media on Sephadex G-75 in 1 M acetic acid yielded a single peak that coeluted with a synthetic E-domain peptide standard. Since secretion of the E-domain peptide parallels the expression of IGF-II, the RIA for the proIGF-II E-domain peptide may be useful for studies of the biosynthesis and secretion of IGF-II under different physiological conditions. The RIA for the IGF-II E-domain peptide has two technical advantages over the RIA for IGF-II, namely, the lack of interference by IGF binding proteins and the relative ease with which large quantities of pure antigen can be synthesized.

Insulin-like immunoreactivity in the brain of two hagfishes, Eptatretus stouti and Myxine glutinosa

Immunocytochemical investigation of the brains of hagfish Myxine glutinosa and Eptatretus stouti with antisera raised against salmon insulin revealed the presence of groups of immunoreactive cells discretely localized in the mid- and hindbrain of both species. Subpopulations of these cells reacted weakly with antisera against Myxine islet insulin and equivocally with anti-bovine insulin serum. Extracts prepared from Myxine brain were subject to gel filtration and were found by radioimmunoassay to contain two forms of insulin-like material, one of large molecular weight (less than 66 kDa) and another smaller molecule (6 kDa). The relationship of these molecules to the insulin-related growth factor family of neurohormonal peptides is discussed and their potential function assessed in terms of a possible homology with Muller-type cells and involvement in axonal regeneration phenomena.

Regulation of hepatic expression of IGF I and fetal IGF binding protein mRNA in streptozotocin-diabetic rats

Hepatic mRNA levels of insulin-like growth factor I (IGF I) and of the fetal, nonglycosylated 32 kDa IGF-binding protein (BP) were analysed in diabetic, diabetic insulin- and IGF I-treated rats as well as in age-matched, healthy control animals. IGF ImRNA levels are reduced in diabetic rats and increased by insulin treatment. In contrast, the infusion of IGF I does not significantly upregulate IGF I mRNA levels. Fetal IGF BP mRNA expression is very low in healthy control animals, but high levels are found in diabetic rats. Insulin therapy lowers fetal IGF BP mRNA levels, whereas IGF I has no effect. We propose that insulin is a major regulator of the 32 kDa IGF BP levels in adult rats.

Insulin increases plasma somatomedin C (IGF-1) concentrations in adult type 1 diabetic patients

The role of insulin in the control of somatomedin release has been investigated in people with Type 1 diabetes. Six patients underwent insulin-induced hypoglycaemia of 20 min duration and 8 patients were studied using the hyperinsulinaemic euglycaemic clamp technique at insulin infusion rates of 0.25, 1.25, 2.5, and 0.25 mU kg-1 min-1 for 1 h at each rate. In the first study plasma insulin concentrations rose from (median, range) 23 (10-36) to 114(60-200) mU l-1 at the onset of hypoglycaemia, and fell to 53 (23-100) mU l-1 after 20 min hypoglycaemia and 30 (15-73) mU l-1 on return to normoglycaemia. Plasma IGF-1 rose from 140 (96-292) to 179 (127-352) micrograms l-1 (p less than 0.05) at the onset of hypoglycaemia and fell to 131 (125-173) micrograms l-1 after 20 min and to 154 (121-287) micrograms l-1 at the end of the study. During hyperinsulinaemia plasma insulin rose from 23 (19-40) mU l-1 at the lowest infusion rate to 61 (33-84) and 148 (68-200) mU l-1 at the two higher infusion rates. Over the same period, plasma IGF-1 increased from 91 (13-203) to 123 (98-182) micrograms l-1 (p less than 0.05) and 109 (84-160) micrograms l-1. There was no correlation between growth hormone levels and IGF-1 in either study. These results suggest that insulin produces short-term increases in IGF-1 levels in man in the absence of a growth hormone response.

Differential effects of follicle-stimulating hormone, insulin, and insulin-like growth factor I on hexose uptake and lactate production by rat Sertoli cells

The stimulatory effects of follicle-stimulating hormone (FSH), insulin, and insulin-like growth factor I (IGF-I) on lactate production and hexose uptake by Sertoli cells from immature rats were studied. The time-courses and the maximal stimulatory effects of FSH, insulin, and IGF-I on lactate production were virtually identical. When Sertoli cells were incubated in the presence of FSH in combination with insulin or IGF-I (submaximal doses), additive but no pronounced synergistic effects were observed. The stimulatory effects of FSH and insulin were not dependent on the presence of extracellular calcium. 2-Deoxy-D-glucose (2-DOG), an analogue of D-glucose, was used to investigate the hexose transport system of Sertoli cells. Uptake of 2-DOG was linear in time and virtually all of the intracellular 2-DOG was phosphorylated up to 30 min of incubation; 2-DOG uptake was inhibited by cytochalasin B, but not by cytochalasin E. D-glucose, but not D-galactose, appeared to be an effective competitor of 2-DOG uptake. The Km of 2-DOG uptake was not influenced by FSH, insulin, and IGF-I. FSH had no effect on the Vmax of 2-DOG uptake, whereas insulin and IGF-I caused a 30% stimulation of the Vmax. It is concluded that FSH, insulin, and IGF-I stimulate lactate production by cultured Sertoli cells, but that only insulin and IGF-I stimulate hexose transport. The insulin-like effect of FSH on Sertoli cells may principally involve stimulation of glycolytic enzyme activities.

Insulin stimulates skeletal growth in vivo and in vitro--comparison with growth hormone in rats

The effect of insulin on skeletal growth was examined by (1) systemic injection, (2) local administration into the tibia growth plate and (3) in vitro by use of chondrocytes in culture. (1) Male rats, body weight 60-75 g, were hypophysectomised. One week after the operation, the animals were divided into three groups. Group A received intraperitoneally saline, group B insulin (5-30 U.kg-1.day-1) and group C human growth hormone (250 micrograms/kg/day) for the following 10 days. In addition, on day 10 the rats were injected with 10 mu-Ci 35-S-sulfate intraperitoneally. Twenty-four h later in the non-fasting state plasma glucose, insulin, somatomedin activity (porcine assay), body weight, nose-rump length, width of the tibia growth plate, and the 35-S-sulfate incorporation into rib cartilage were determined. Compared to saline, growth hormone and insulin treatment significantly enhanced body weights, nose-rump lengths, the widths of the proximal tibia growth plates and the incorporation of sulfate into rib cartilage. For the three skeletal growth parameters, growth hormone was more effective than insulin, while body weights did not differ after insulin or growth hormone treatment. Somatomedin activity (U/ml) was low in group A (0.39 +/- 0.04, n = 9, Mean +/- SEM) and group B (0.34 +/- 0.08, n = 8) and high in the growth hormone treated group C (0.90 +/- 0.09, n = 7; p less than 0.002). (2) To test the possibility that insulin might directly augment skeletal growth, insulin (80 mU) was injected into the proximal tibia growth plate of one leg and saline into the cartilage zone of the other leg.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth promoting effects of IGF-I on fetal hypothalamic cell lines under serum-free culture conditions

Recent evidence indicates that the insulin-like family of peptides may act as endogenous trophic factors in the central nervous system. To further examine this possibility we have investigated the effects of three insulin-like peptides on the in vitro growth of fetal hypothalamic cell lines. Two virally transformed rat hypothalamic cell lines which have been developed in our laboratory (A-6 and F-12) were used. Cells were plated at varying densities and cultured in the presence or absence of either insulin-like growth factor I (IGF-I), insulin, or multiplication stimulating activity (MSA or IGF-II), in serum-free medium for 1 wk. Cell growth was assessed by counting or by measuring cellular incorporation of 3H-thymidine. Of the three peptides tested IGF-I was the most potent in eliciting cell growth. Insulin also stimulated growth of both cell lines, but was 100 times less potent for A-6 cells while it was equipotent with IGF-I in F-12 cells. MSA had no effect on either cell line. Both IGF-I and insulin showed dose-response effects in increasing cell growth. We also found that the two cell lines had the greatest response to IGF-I at low cell densities. Finally, time-course experiments suggested that a continued presence of the peptide is essential for the growth-promoting effects. We conclude that IGF-I is a potent growth factor for virally transformed cell lines derived from the rat fetal hypothalamus. Since both IGF-I immunoreactivity and IGF-I receptors have been located in this diencephalic area these results suggest that IGF-I may constitute a mitogenic signal for hypothalamic cells during neurogenesis.

Recombinant DNA-derived human insulin-like growth factor II (hIGF-II) stimulates growth in hypophysectomized rats

Sustained subcutaneous administration of recombinant DNA-derived insulin-like growth factor II to immature female hypophysectomized rats stimulated significant increases in body weight gain, tibial epiphyseal cartilage width, femur hydroxyproline concentrations and a significant decrease in serum urea nitrogen concentrations. Recombinant DNA-derived human growth hormone (Humatrope), administered in the same manner produced similar biological effects. The data support the contention that hIGF-II has anabolic effects when administered to hypophysectomized rats and may be a locally acting mediator of pituitary hormone actions.

Purification of the serum acid-stable insulin-like growth factor binding protein from the pig (Sus scrofa)

1. An acid-stable IGF binding protein was isolated and purified from porcine serum. 2. The protein comprised two major species with Mrs of 45 and 41 kDa determined using SDS-PAGE under reducing conditions. 3. The IGFBP preparation specifically bound both IGF-I and II. 4. Four distinct protein bands (Mrs of 23, 45, 50 and 75 kDa) in the porcine IGFBP preparation specifically bound radiolabelled IGF-I. 5. The porcine IGFBP exhibited sequence homology with IGFBPs from human plasma and rat serum. 6. This is the first report of the purification and characterization of the acid-stable IGFBP from porcine serum.

Insulin-like growth factors and insulin increase the contractility of neonatal rat cardiocytes in vitro

In the newborn several situations of hyperinsulinism can be associated with myocardial hypertrophy and increased contractility. Insulin and the insulin-like growth factors (IGF) are derived from a common ancestral molecule. Insulin exerts mainly metabolic action, whereas the IGFs promote cell multiplication and differentiation. Using an assay system of cultured neonatal myocardial cells the stimulatory action of insulin and the insulin-like growth factors I and II on myocardial cell contractility was investigated. Spontaneously beating aggregates of myocardial cells were synchronized by an electric impulse generator. Contractility was measured via the amplitude of contraction by an optoelectronic system. Insulin at a concentration of 6,250 and 12,500 microU/ml increased the contractility by 11 and 18%; IGF-I at a concentration of 12 and 25 ng/ml, and IGF-II at a concentration of 25 and 50 ng/ml increased the contractility by 16 and 22%, and 13 and 18%, respectively. Lower concentrations did not provoke a significant increase in contractility. Insulin only in supraphysiological doses increases the contractility of neonatal myocardial rat cells, whereas both insulin-like growth factors act in physiological concentrations. Therefore, during hyperinsulinism insulin may increase myocardial contractility via the IGF receptor and not via the insulin receptor.

Localization of binding sites for insulin-like growth factor-I (IGF-I) in the rat brain by quantitative autoradiography

In vitro quantitative autoradiography was used to localize IGF-I binding sites in rat brain. Slide-mounted sections of frozen rat brain were incubated in 0.01 nM 125I[Thr59]IGF-I, alone or mixed with 10 nM unlabeled [Thr59]IGF-I or insulin, for 22 h at 4 degrees C and apposed to LKB Ultrofilm. Measurement of labeled [Thr59]IGF-I binding by computer digital image analysis of the autoradiographic images indicated that high affinity IGF-I binding sites are widely distributed at discrete anatomical regions of the brain microarchitecture. The highest concentration of specific binding sites was in the choroid plexus of the lateral and third ventricles. Unlabeled porcine insulin was less potent than unlabeled IGF-I in competing for binding sites on brain slices. Regions of the olfactory, visual, and auditory, as well as visceral and somatic sensory systems were labeled, in particular the glomerular layer of the olfactory bulb, the anterior olfactory nucleus, accessory olfactory bulb, primary olfactory cortex, lateral-dorsal geniculate, superior colliculus, medial geniculate, and the spinal trigeminal nucleus. High concentrations of IGF-I-specific binding sites were present throughout the thalamus and the hippocampus, (dentate gyrus, Ca1, Ca2, Ca3). The hypothalamus had moderate binding in the paraventricular, supraoptic, and suprachiasmatic nucleus. Highest binding in the hypothalamus was in the median eminence. The arcuate nucleus showed very low specific binding, approaching the levels found in optic chiasm and white matter regions. Layers II and VI of the cerebral cortex also had moderate IGF-I binding. The results suggest that the development and functions of brain sensory and neuroendocrine pathways may be regulated by IGF-I.