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D R Clemmons

Publications and source records attributed to D R Clemmons.

At least 181 records · Page 10Linked to original sources
PubMed1989

Identification of the types of insulin-like growth factor-binding proteins that are secreted by muscle cells in vitro.

We have previously shown that muscle cells secrete insulin-like growth factor-binding proteins. In the present study, BC3H-1 cells were shown to secrete one binding protein of Mr 32,000, whereas L6 cells secreted two binding proteins of Mr 31,000 and 24,000, as determined by ligand blotting. Subconfluent proliferating L6 cells secrete more of the Mr 24,000 binding protein, relative to the Mr 31,000 form. In contrast, differentiated L6 myotubes secreted similar quantities of the two forms. Insulin-like growth factor I preferentially stimulated secretion of the Mr 31,000 versus the Mr 24,000 binding protein from L6 cells and caused an increase in the secretion of the Mr 32,000 binding protein from BC3H-1 cells. The Mr 31,000 binding protein from L6 cells had a greater affinity for insulin-like growth factor II compared with insulin-like growth factor I, as did the Mr 32,000 binding protein of BC3H-1 cells. In contrast, the Mr 24,000 binding protein of L6 cells preferred insulin-like growth factor I. Neither porcine insulin nor relaxin competed for 125I-IGF-I binding. In conclusion, these muscle cell lines secrete only one or two forms of insulin-like growth factor-binding proteins. L6 cell differentiation is associated with a relative increase in the secretion of the Mr 31,000 binding protein compared with the Mr 24,000 form. Insulin-like growth factor I stimulates the secretion of its own binding proteins from muscle cells, and this may be an important mechanism for modulating cellular responsiveness to this growth factor.

Animals↗
PubMed1989

Structural and functional analysis of insulin-like growth factors.

The insulin and insulin-like growth factor family of peptides are proteins with similar structural characteristics whose functions have diverged during evolution. Recent studies have provided a great deal of information regarding structural characteristics of these peptides, the structures of the genes that control their biosynthesis, and determination of their receptor structures. Initially these factors were believed to function as classical hormones and the endocrine regulation of their blood concentrations was studied intensively. More recently several cell types have been shown to secrete these peptides and the autocrine and paracrine regulation of insulin-like growth factor secretion by cells and tissues has received extensive characterization. Following secretion into interstitial fluids the IGF's associate with high affinity, soluble binding proteins. These proteins are capable of modulating receptor binding and growth factor biological activity. The structure of these proteins and the variables that control their secretion are currently being determined. In spite of this information significant gaps in our knowledge exist regarding the mechanisms by which these peptides stimulate replication.

Animals↗
PubMed1989

The insulin-like growth factor-binding proteins of porcine serum: endocrine and nutritional regulation.

Several studies have shown that insulin-like growth factor-binding proteins (IGF-BPs) modify IGF activity. To investigate their role in regulating growth, the number and size of IGF-BPs in porcine serum and the role of nutritional and endocrine factors in controlling their relative abundance were determined. IGF-BPs were analyzed by ligand blotting; sera were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, then the separated proteins were transferred to nitrocellulose filters and probed with [125I]IGF-I or -II. The band intensities of various forms of IGF-BPs were quantified by scanning densitometry. Fetal and postnatal sera contained six IGF-BPs of 220,000, 43,000, 39,000, 34,000, 29,000, and 24,000 mol wt (Mr). The band intensity of all forms of IGF-BPs increased with advancing gestational age. Specifically, the intensities of the 43,000, 39,000, 34,000, 29,000, and 24,000 Mr IGF-BP bands were 2.8-, 2.7-, 4.3-, 4.4-, and 3.1-fold higher, respectively, in fetal plasma at 110 than at 45 days gestation. In fetal plasma the 34,000 and 29,000 Mr forms predominated, whereas postnatally, the 43,000 and 39,000 Mr IGF-BPs predominated. Fasting of newborn pigs for 24 h reduced the intensity of the 43,000, 39,000, 34,000, and 24,000 Mr forms to 11.5%, 7.2%, 69.8%, and 5.2% of control levels, respectively. However, the 29,000 Mr IGF-BP was 1.8-fold higher in fasted pig serum than in that of fed controls. The band intensities of the 34,000 and 29,000 Mr forms were increased in postnatal animals after hypophysectomy. In contrast, fetal decapitation resulted in a preferential decrease in only the 34,000 Mr form, which was reduced by 30% compared to that in age-matched controls. These studies indicate that porcine serum contains six IGF-BPs that can be detected by ligand blotting. The level of each of these proteins increases with advancing gestational age, although the increases are not uniform, suggesting that the proteins may be regulated differentially. In the postnatal animal both endocrine and nutritional factors modulate the levels of IGF-BPs by distinct controlling mechanisms.

Animal Nutritional Physiological Phenomena↗
PubMed1989

Purified preparations of the amniotic fluid-derived insulin-like growth factor-binding protein contain multimeric forms that are biologically active.

The insulin-like growth factors (IGFs) appear to be secreted into interstitial fluids by many cell types, along with specific, high affinity binding proteins (IGF-BPs). These proteins, therefore, have the potential to bind IGF-I and -II and modify their ability to interact with specific cell surface receptors In these studies we report the detection of high mol wt, multimeric forms of one form of IGF-BP that has been purified from human amniotic fluid. The multimeric forms, which are either not or barely detectable in native amniotic fluid, are the result of intermolecular disulfide bond formation and can be reduced to a monomeric form by exposure to dithiothreitol. After reduction, the multimers are reduced to either monomeric or dimeric forms, as detected by Western blotting. The multimers can be separated from monomeric and dimeric forms by gel filtration chromatography. The purified multimers were fully biologically active in potentiating the effect of IGF-I on porcine aortic smooth muscle cell DNA synthesis. The monomeric form was also bioactive. No significant differences in the affinity of the monomeric and multimeric forms for IGF-I or -II could be detected. In summary, multimeric forms of this form of IGF-BP are detected during purification. The formation of these multimers is through intermolecular disulfide bonds and does not disrupt IGF binding or potentiation of the cellular growth response to IGF-I. These findings indicate that these higher mol wt forms may be fully active in biological test systems.

Amniotic Fluid↗
PubMed1989

Insulin-like growth factor-I (IGF-I) infusion into hypophysectomized or protein-deprived rats induces specific IGF-binding proteins in serum.

The insulin-like growth factors (IGFs) are small peptides that are present in serum and extracellular fluids and stimulate the growth of many cell types. In extracellular fluids the IGFs are bound to carrier proteins that are believed to modify the biological actions of the IGFs. At least three structurally distinct IGF-binding proteins (IGF-BPs) have been identified, and the serum concentrations of one of these has been shown to be regulated by pituitary GH. We report here that this GH responsive protein [39,000-45,000 mol wt (Mr)] can be induced (7-fold) by infusion of IGF-I in hypophysectomized rats or (3.5-fold) in protein-deprived rats, whereas two other forms of IGF-BP (e.g. 31,000-34,000 and 24,000 Mr) showed no change in the hypophysectomized animals and minimal increases in the protein-deprived animals. Likewise, GH injections in hypophysectomized animals resulted in a 7-fold increase in the 39,000-45,000 Mr form and no change in the 31,000-34,000 and 24,000 Mr forms. The protein-deprived animals showed a 3.2-fold increase in the 39,000-45,000 Mr and 2.4- to 1.8-fold increases in the 31,000-34,000 and 24,000 Mr forms, respectively. Changes in the larger Mr IGF-BP in these experimental models are paralleled by changes in serum IGF-I, suggesting that the GH dependence of the former protein is mediated at least partially via IGF-I. Our findings also suggest that the secretion of IGF-I and at least one IGF-BP may be linked, providing a mechanism by which their extracellular fluid concentrations are coordinated. Because IGF-BPs are present in extracellular fluids and can modulate IGF-I-receptor interaction, induction of this protein may be an important mediator of IGF action.

Animals↗
PubMed1989

Dietary carbohydrate content determines responsiveness to growth hormone in energy-restricted humans.

To determine if diet composition influences responses to GH, we fed 11 obese women diets containing 12 Cal/kg ideal BW (IBW) for 2 5-week study intervals. Nonprotein calories were supplied to 6 subjects as 72% carbohydrate (high carbohydrate diet), and 5 subjects received 80% of their nonprotein calories as lipid (high lipid diet). Protein intake was constant (1.0 g/kg IBW) in both groups. During 1 study interval we gave injections of GH (0.1 mg/kg IBW) every other day for 3 weeks (weeks 2-4), and in the other interval injections of vehicle were given. Subjects ingesting the high carbohydrate diet excreted significantly less urinary nitrogen [660.2 +/- 124.1 mmol/day (mean +/- SD)] than those who received high lipid (794.2 +/- 198.5 mmol/day; P less than 0.001), and GH injections reduced nitrogen excretion in the high carbohydrate subjects (532.8 +/- 123.8 mmol/day), but not in the high lipid subjects (743.7 +/- 126.6 mmol/day). The subjects receiving the high carbohydrate diet had a significant increase in serum insulin-like growth factor-I (IGF-I; from 36.2 +/- 9.7 to 55.9 +/- 6.6 nmol/L) and urinary C-peptide excretion (from 43.9 +/- 25.6 to 60.8 +/- 29.4 nmol/day) in response to GH. The IGF-I response attenuated slowly over the 3-week treatment interval. On the other hand, the high lipid group had lesser increases in IGF-I (from 31.0 +/- 6.5 to 41.7 +/- 8.8 nmol/L) and C-peptide excretion (from 24.3 +/- 28.9 to 29.8 +/- 32.8 nmol/day), and IGF-I concentrations declined to control values after only 5 days of GH injection. We believe that this initial IGF-I response was due to an antecedent 35-Cal balanced diet. The mean increment in serum FFA 4 h after GH injection was significantly less in subjects fed the high lipid diet (0.53 +/- 0.40 meq/L) than in those fed the high carbohydrate diet (0.83 +/- 0.43 meq/L). GH injections produced more body fat loss than injections of vehicle whether expressed as percent body fat lost (GH, 3.7 +/- 1.0%; vehicle, 2.8 +/- 0.7%, P less than 0.05) or as the fraction of weight lost as fat (fat loss/weight loss; GH, 0.81 +/- 0.13; vehicle, 0.64 +/- 0.08; P less than 0.005). There was an inverse correlation between the percentage of body fat lost and mean urinary C-peptide excretion during GH injections (r = -0.70; P less than 0.05), suggesting that stimulation of insulin secretion by GH might antagonize the tendency of GH to promote fat loss.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1989

Immunological distribution of one form of insulin-like growth factor (IGF)-binding protein and IGF peptides in human fetal tissues.

Insulin-like growth factors (IGFs) are expressed by, and are biologically active on, human fetal cells. The mitogenic actions of IGF-I are modulated by the 21-41 kDa class of IGF-binding proteins (IGF-BPs). Using a rabbit anti-human IGF-BP antibody raised against a highly pure 26 kDa IGF-BP derived from amniotic fluid, we have compared the cellular location of IGF-BP and IGF peptides in tissue sections from prostaglandin-induced human abortuses of 14-16 weeks of gestation. The monoclonal and polyclonal antibodies used were raised against human IGF-I, but did not distinguish between IGF-I and IGF-II. Positive staining for IGF-BP was seen in every tissue except brain, spleen and thyroid. With the exception of skin, the cellular distribution of IGF-BP was similar to that of IGF peptides. Strong immunostaining was found in hepatocytes, hepatic erythropoietic cells, pulmonary epithelium, the tubular epithelium of kidney, intestinal epithelia, the fetal adrenal cortex and cardiac and skeletal muscle fibres. In skin, IGF-BP was located throughout the dermis and in the germinal layer of the epidermis. IGF peptide in skin was restricted to the deeper dermal layers. In the tibial epiphyseal growth plate both IGF-BP and IGF peptide were located in chondrocytes throughout the proliferation and hypertrophic zones. The similarity in distribution of IGF-BP and IGF peptides in fetal tissues suggests that the latter may exist predominantly complexed to IGF-BP in or on the surfaces of cells in vivo. The distribution of IGF-BP may define the sites of biological action of IGF peptides.

Adrenal Cortex↗
PubMed1989

Insulin-like growth factor (IGF)-binding protein release by human fetal fibroblasts: dependency on cell density and IGF peptides.

Insulin-like growth factors (IGFs) are bound to specific binding proteins in extracellular fluids in vivo and when released by cells in vitro. One class of binding protein (IGF-BP), a peptide of 26 kDa purified from amniotic fluid, has been shown to modulate IGF bioactivity on isolated human fibroblasts. We have determined the factors that control release of IGF-BP from monolayers of human fetal fibroblasts using a radioimmunoassay, and have compared this with the effects of these factors on the release of IGF-I and -II. Separation of cell-conditioned cultured medium on SDS-PAGE, and subsequent immunoblotting with antibody against IGF-BP showed that fibroblasts released a single species of immunoreactive protein of an estimated molecular weight of 30 kDa. This was not the predominant binding protein released by cells since major bands of approximately 42 kDa and 39 kDa were visualized following separation by SDS-PAGE and ligand blotting with 125I-labelled IGF-I. The 30 kDa IGF-BP was released in parallel with radioimmunoassayable IGF-I and -II over 48 h. However, a significant inverse correlation was found between the release of IGF-BP, IGF-I, IGF-II and cell density. The exposure of fibroblasts to 1.3 nmol/l or greater of IGF-I or -II caused a significant release of IGF-BP. Maximum release was seen in sparse cultures with little or no release from confluent cultures. IGF-I and -II were approximately equipotent with a fourfold increase in IGF-BP release at 19.7 nmol/l. Insulin caused a release of IGF-BP and IGF-I and -II from fibroblasts at supraphysiological concentrations (16.7 nmol/l) which again was maximal on sparse cell cultures. Increases in IGF-BP, IGF-I and -II release were also found in the presence of human placental lactogen (23.3 nmol/l), but human GH, epidermal growth factor, fibroblast growth factor and platelet-derived growth factor were without effect. The results show that human fetal fibroblasts released an IGF-BP immunologically similar to that seen in amniotic fluid together with IGF-I and -II, that IGF-BP release was enhanced by exogenous addition of IGF peptides, and that the release of all three peptides was a property of sparsely plated, rapidly growing cells. These findings strengthen the hypothesis that the cellular expression of IGF-binding proteins may represent an important level of control in IGF physiology.

Carrier Proteins↗
PubMed1988

Purification of a 31,000-dalton insulin-like growth factor binding protein from human amniotic fluid. Isolation of two forms with different biologic actions.

Human amniotic fluid has been shown to contain a protein that binds insulin-like growth factor I and II (IGF-I and IGF-II). Partially purified preparations of this protein have been reported to inhibit the biologic actions of the IGFs. In these studies our laboratory has used a modified purification procedure to obtain a homogeneous preparation of this protein as determined by polyacrylamide gel electrophoresis and amino acid sequence analysis. During purification the ion exchange chromatography step resulted in two peaks of material with IGF binding activity termed peaks B and C. Each peak was purified separately to homogeneity. Both peaks were estimated to be 31,000 daltons by polyacrylamide gel electrophoresis and their amino acid compositions were nearly identical. Amino acid sequence analysis showed that both peaks had identical N-terminal sequences through the first 28 residues. Neither protein had detectable carbohydrate side chains and each had a similar affinity for radiolabeled IGF-I (1.7-2.2 x 10(10) liters/mol). In contrast, these two forms had marked differences in bioactivity. Concentrations of peak C material between 2 and 20 ng/ml inhibited IGF-I stimulation of [3H]thymidine incorporation into smooth muscle cell DNA. In contrast, when peak B (100 ng/ml) was incubated with IGF-I there was a 4.4-fold enhancement of stimulation of DNA synthesis. Additionally, pure peak B was shown to adhere to cell surfaces, whereas peak C was not adherent. The non-adherent peak C inhibited IGF-I binding to its receptor and to adherent peak B. We conclude that human amniotic fluid contains two forms of IGF binding protein that have very similar physiochemical characteristics but markedly different biologic actions. Since both have similar if not identical amino acid compositions, N-terminal sequences, and do not contain carbohydrate, we conclude that they differ in some other as yet undefined post-translational modification.

Amino Acid Sequence↗
PubMed1988

Cloning, characterization, and expression of a human insulin-like growth factor binding protein.

Insulin-like growth factors (IGFs) bind to specific proteins present in extracellular fluids. One of these binding proteins (IGF-BP) was purified from human amniotic fluid and was shown to potentiate the effects of IGF-I in vitro (10). In these studies, a polyclonal antibody to this protein was used to isolate a cDNA clone from a human decidua library. This clone encodes a polypeptide of 25,832 daltons that includes the sequences of 9 tryptic peptides that had been prepared from the purified IGF-BP. The protein has 15 cysteines that are clustered at the amino and carboxy ends of the molecule. The protein has an RGD sequence near its C-terminus, which may account for its ability to attach to cells and to potentiate the biological actions of IGF-I.

Amino Acid Sequence↗
PubMed1988

Insulin-like growth factor binding protein secretion by muscle cells: effect of cellular differentiation and proliferation.

Several cell types have been shown to secrete insulin-like growth factor binding proteins (IGF-BP) in vitro. Since IGF-BP influences cell responsiveness to IGF, three muscle cell types were investigated to determine if they produced IGF-BP and to identify factors that regulate IGF-BP secretion. Porcine smooth muscle cells (pSMC), rat L6 skeletal muscle cells, and mouse BC3H-1 myocytes were used. IGF-BP activity in serum-free conditioned media was quantitated with a polyethylene glycol precipitation method. All three cell types secreted IGF-BP activity into the medium. Insulin was a potent stimulant of IGF-BP secretion for each cell type. Specifically, 1 microgram/ml insulin increased the IGF-BP concentration in conditioned media from 10.5 +/- 1.3 to 15.0 +/- 1.5 ng/ml in confluent L6 myotubes, from 42.5 +/- 11.1 to 90.5 +/- 9.8 ng/ml in confluent BC3H-1 cells, and from 2.1 +/- 0.1 to 3.8 +/- 0.1 ng/ml in confluent pSMC. L6 myotubes required more insulin (8 micrograms/ml) to achieve a half-maximal stimulation of IGF-BP secretion than confluent pSMC, differentiation deficient L6.DD cells or BC3H-1 cells, where half-maximal stimulation occurred between 125 and 300 ng/ml. L6 myoblasts were 40-fold more sensitive to insulin stimulation of IGF-BP secretion than L6 myotubes. IGF-I, although it interferes with the assay and thereby lowers the amount of detectable IGF-BP, stimulated the secretion of IGF-BP from all three cell types. Dexamethasone, (10(-7) M) decreased IGF-BP secretion into the media by approximately 50% for all three cell types. Affinity cross-linking and ligand blotting of 125I-IGF-I to conditioned media from each cell type showed (IGF-BP)-(IGF-I) complexes with molecular weights ranging 32-40 kDa (24-32 kDa for IGF-BP and 7.5 kDa for IGF-I). Insulin stimulated cell proliferation for both L6 myoblasts and BC3H-1 myocytes. This cell proliferative response was associated with an increase in IGF-BP secretion/cell in response to insulin. In contrast dexamethasone decreased L6 myoblast proliferation and decreased IGF-BP secretion/cell. We conclude that IGF-BP is secreted by each muscle cell type and that the state of cellular differentiation or quiescence influences its basal and insulin-stimulated secretion. Insulin and IGF-I are stimulators of IGF-BP secretion, whereas dexamethasone inhibits IGF-BP secretion. Because these hormones control muscle cell growth and differentiation, the IGF-BP may play an important regulatory role in these processes.

Animals↗
PubMed1988

The ontogeny and regulation of a 31,000 molecular weight insulin-like growth factor-binding protein in fetal porcine plasma and sera.

Studies were conducted to determine the presence, quantity, and regulation of insulin-like growth factor (IGF)-binding proteins in porcine plasma and sera. The size distribution of IGF-binding protein was determined by affinity cross-linking to [125I]IGF-I, and the binding activity was quantified by a polyethylene glycol precipitation procedure. The major [125I]IGF-I-binding protein complex was of 38,000 mol wt (Mr) in all porcine sera or plasma tested. Binding to this protein was inhibited by excess unlabeled IGF-I, but not by insulin. When plasma samples from fetuses at 45, 70, 90, and 110 days gestation were cross-linked to [125I]IGF-I, there was an increase in the concentration of the 38,000 Mr complex with advancing gestational age, whereas plasma from the mothers of the age-matched fetuses showed little change in the amount of the 38,000 Mr complex. When the binding activity of the fetal plasma was quantified, there was a significant increase in binding activity between 45 and 110 days gestation from 30.5 +/- 3.3% to 77.5 +/- 3.6% (+/- SE) of the assay maximum. This increase was not due to a decrease in binding protein saturation, since the endogenous IGF-I levels (quantified after acid gel filtration chromatography) also increased with advancing gestational age, from 176 to 458 mU/ml. Blood samples were collected from porcine fetuses at 110 days gestation that had either been decapitated or spinal cauterized at 45 days gestation. Decapitation decreased the amount of the 38,000 Mr complex that could be detected by affinity labeling. In contrast, spinal cauterization had no effect on the amount of the 38,000 Mr complex in fetal plasma compared to that in control fetal plasma. These results were verified in the polyethylene glycol assay. These studies show that the amount of the 38,000 Mr IGF-binding protein complex in pig plasma is developmentally regulated and suggest that a pituitary or neural factor may be an important variable in the control of its plasma concentrations.

Animals↗
PubMed1988

Both type I and II insulin-like growth factor receptor binding increase during lactogenesis in bovine mammary tissue.

Bovine GH is a potent stimulant of lactation, and the insulin-like growth factors I and II (IGF-I and -II) are believed to mediate GH's growth-promoting actions. Since all of IGF's known actions are mediated through its receptor subtypes, we analyzed the distribution of IGF receptor subtypes in lactating and nonlactating bovine mammary tissue. Analysis of competition curves showed that IGF-I had greater potency than IGF-II in competing with [125I]IGF-I for binding to membranes prepared from both lactating and nonlactating animals. An insulin concentration of 4 micrograms/ml displaced less than 40% of the [125I]IGF-I bound to membranes prepared from both lactating and nonlactating animals, indicating that a high percentage of [125I]IGF-I was bound to the type II receptor. Lactation was associated with an increase in the total amount of [125I]IGF-I bound, and this change was due to an increase in binding to both receptor subtypes. Specifically, membranes prepared from lactating animals had a 3-fold increase in binding competed for by insulin and a 2-fold increase in binding not competed for by insulin. Affinity cross-linking of [125I]IGF-I to membranes prepared from both lactating and nonlactating animals, followed by polyacrylamide gel electrophoresis (PAGE) and autoradiography, showed that 260K and 135K bands were present. Competition experiments indicated that unlabeled IGF-I effectively competed for binding to the 260K band, whereas insulin did not. Binding to the 135K band could be inhibited by both IGF-I and insulin. The intensity of the labeled bands showed that type II receptors were relatively more abundant than type I receptors in membranes from both lactating and nonlactating animals. Membranes prepared from lactating animals showed both 135K and 127K species of the type I receptor, whereas nonlactating animals showed only the 135K band. We conclude that type I and II receptors are present in bovine mammary tissue, and type II predominate. Lactation is associated with increases in the concentration of both receptor subtypes, especially type I receptors. Lactation may be associated with structural changes in the type I receptor. These changes in receptor distribution could play a role in modulating the physiological effects of the IGFs on mammary tissue.

Animals↗
PubMed1988

Treatment of obese, diet-restricted subjects with growth hormone for 11 weeks: effects on anabolism, lipolysis, and body composition.

We found in a previous study that injections of GH for 3 weeks caused nitrogen conservation despite restriction of intake to 24 Cal (100 kJ)/kg ideal BW (IBW). To determine the effects of longer periods of treatment and further caloric restriction on nitrogen balance, lipolysis, and body composition, 20 obese (30-67% over IBW) subjects (16 women and 4 men; 20-54 yr old) were fed a diet of 18 Cal (75 kJ)/kg IBW with 1.2 g protein/kg IBW daily for 13 weeks. During weeks 2-12, 10 subjects received injections of recombinant methionyl GH (0.1 mg/kg IBW every other day), and the other 10 sex-, age-, and weight-matched subjects were given injections of saline. There were no significant differences between the two groups in total weight loss [GH, 13.9 +/- 3.0 (+/- SD) kg; saline, 15.2 +/- 3.8 kg ) or the percentage of body fat lost (GH, 8.1 +/- 2.4%; saline, 7.5 +/- 1.5%), although GH injection caused a significant acute increment in serum FFA concentrations (GH, 0.53 +/- 0.37 mmol/L; saline, 0.08 +/- 0.22 mmol/L; P less than 0.001) throughout the study. This acute lipolytic response to GH decreased significantly, from 0.86 +/- 0.32 mmol/L on day 1 of GH treatment to 0.35 +/- 0.41 mmol/L by day 35 of GH injection (P less than 0.01). Nitrogen balance was significantly more positive in the group receiving GH during the first 33 days of the GH injection period [GH, +0.07 +/- 1.82 g/day (+5.0 +/- 130.0 mmol/day); saline, -1.91 +/- 1.10 g/day (-136.3 +/- 78.5 mmol/day); P less than 0.001]. During the last 44 days of GH injection, however, the nitrogen balance in the two groups was similar [GH, -0.90 +/- 1.65 g/day (-64.2 +/- 117.8 mmol/day); saline, -1.08 +/- 0.95 g/day (-77.1 +/- 67.8 mmol/day); P = NS]. Mean plasma insulin-like growth factor I (IGF-I) concentrations rose from a basal value of 1.6 +/- 0.8 to 2.9 +/- 1.2 U/mL by 48 h after the first GH injection and ranged subsequently from 3.2 +/- 1.3 to 4.9 +/- 3.3 U/mL during GH injection (P less than 0.001). In contrast, the mean IGF-I concentration did not change in the group that received saline. Dietary restriction during the first week of study caused serum T3 concentrations to decline in both groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1988

Radioimmunoassay of a 26,000-dalton plasma insulin-like growth factor-binding protein: control by nutritional variables.

Insulin-like growth factor I (IGF-I) is a peptide growth factor that circulates bound to carrier proteins. One form of carrier protein (mol wt, approximately 26K) is not believed to be GH dependent, is relatively unsaturated, and modulates the cellular response to IGF-I. This study was undertaken to determine the variables that control the plasma concentration of this protein, which was measured using a specific RIA. The mean plasma 26K IGF-binding protein (IGF-BP) concentration in 15 normal fasting subjects at 0800 h was 9.4 +/- 4.4 (+/- SD) micrograms/L. The mean value in GH-deficient patients was increased to 19.5 +/- 10.1 micrograms/L (n = 60; P less than 0.05), and it was 7.3 +/- 4.3 micrograms/L in patients with acromegaly (n = 31). The GH dependency of these changes is further supported by the observation that subjects who received GH injections had a 51% reduction in their fasting values. Nutritional intake appeared to be a more important controlling variable than GH. During an overnight fast plasma 26K IGF-BP values increased approximately 4-fold in 6 normal subjects. After 2 days of fasting, the mean value in 7 obese subjects rose progressively from 6.5 +/- 2.3 to 11.7 +/- 5.4 micrograms/L (P less than 0.001), and it increased further to 19.2 +/- 5.9 micrograms/L by day 4 of fasting; after 2 days of refeeding it returned to the prefasting level of 6.8 +/- 1.9 micrograms/L. Likewise, ingestion of a standard test meal resulted in a significant decrease in mean plasma 26K IGF-BP from a fasting value of 8.4 +/- 2.9 to 5.6 +/- 2.8 micrograms/L 4 h postprandially (P less than 0.05). In summary, the plasma concentrations of the 26K IGF-I-BP fluctuate widely in response to dietary manipulation, whereas GH status appears to be a secondary controlling variable.

Adult↗
PubMed1988

Serum concentrations of insulin-like growth factor II are not changed by short-term fasting and refeeding.

To determine the factors that regulate insulin-like growth factor II (IGF-II), we raised polyclonal antibodies to this peptide and developed a RIA that measures IGF-II in serum or plasma samples after extraction of IGF-binding proteins by C18 cartridge chromatography. The IGF-II antiserum was highly specific, exhibiting no cross-reactivity with IGF-I or insulin at the highest concentrations tested (10(-6) mol/L). As little as 0.43 micrograms/L IGF-II was detectable, and 50% displacement of tracer occurred at 1.7 microgram/L. The serum IGF-II concentrations of normal adults [mean, 634 +/- 170 (+/- SD) micrograms/L], patients with acromegaly (570 +/- 146 micrograms/L), and patients with hypopituitarism (156 +/- 58 micrograms/L) were similar to those reported by others. In eight obese subjects injected with GH (0.1 mg/kg ideal BW, im, every 48 h for 16 days), serum IGF-II concentrations did not rise significantly, whereas IGF-I concentrations increased 67%. Sixteen normal subjects, within 15% of ideal body weight, were fasted for 5 days on two to four occasions and refed diets of differing protein and calorie contents. Their mean serum IGF-II concentration before fasting (691 +/- 26 micrograms/L) was not significantly different from that after fasting (674 +/- 21 micrograms/L) or after refeeding (641 +/- 20 micrograms/L). In contrast, their mean IGF-I concentration decreased 42% with fasting and rose with refeeding. Unlike IGF-I, serum IGF-II concentrations do not appear to be regulated by short term changes in nutritional status. It is clear from this study and others that IGF-II and IGF-I are regulated differently despite their structural homology and the similarity of their actions in vitro.

Adult↗
PubMed1988

Structure of the rat insulin-like growth factor II transcriptional unit: heterogeneous transcripts are generated from two promoters by use of multiple polyadenylation sites and differential ribonucleic acid splicing.

The rat insulin-like growth factor II (rIGF-II) gene, which exists as a single copy in the genome, is expressed as a multitranscript family of mRNA molecules ranging in size from 4.6 to 1 kilobases. Part of this heterogeneity can be ascribed to the presence of two different promoters, each transcribing alternative 5'-noncoding regions which are spliced to common coding exons. In the present study we use a combination of DNA sequence analysis of the gene, mapping of the mRNA molecules by Northern analysis and ribonuclease protection experiments, and DNA sequence analysis of cDNA clones complementary to different regions of the genome to establish the structure of several rIGF-II mRNA species. These results indicate that RNA heterogeneity also arises from the use of different polyadenylation sites. In addition, a variant 2 kilobases RNA was observed that was colinear with the distal 1700 base pairs of the 3147 base pair long exon 3, and may arise by alternative RNA splicing. These posttranscriptional modifications of RNAs arising from the rIGF-II transcription unit may generate molecules with different functional potential.

Animals↗