scholarly journals Amniotic IGF-I supplementation of growth-restricted fetal sheep alters IGF-I and IGF receptor type 1 mRNA and protein levels in placental and fetal tissues

2005 ◽  
Vol 186 (1) ◽  
pp. 145-155 ◽  
Author(s):  
S Shaikh ◽  
F H Bloomfield ◽  
M K Bauer ◽  
H H Phua ◽  
R S Gilmour ◽  
...  
Keyword(s):  
Late Gestation ◽  
Mrna Levels ◽  
Rt Pcr ◽  
Igf Binding Proteins ◽  
Fetal Sheep ◽  
Hepatic Expression ◽  
Protein Levels ◽  
Igf I ◽  
Igf Receptor

We have previously reported that chronic intra-amniotic supplementation of the late gestation growth-restricted (IUGR) ovine fetus with IGF-I (20 μg/day) increased gut growth but reduced liver weight and circulating IGF-I concentrations. Here we report mRNA and protein levels of IGF-I, the type 1 IGF receptor (IGF-1R) and IGF-binding proteins (IGFBP)-1, -2 and -3 in fetal gut, liver, muscle and placenta from fetuses in that earlier study in an attempt to explain these contrasting results. mRNA and protein were extracted from tissues obtained at post mortem at 131 days of gestation (term, 145 days) from three groups of fetuses (control, IUGR+saline and IUGR+IGF-I, n=9 per group). Control fetuses were unembolised and untreated. In the IUGR groups, growth restriction was induced from 113 to 120 days by placental embolisation; from 120 to 130 days fetuses were treated with daily intra-amniotic injections of either saline or 20 μg IGF-I. mRNA was measured by RT-PCR or real-time RT-PCR, and protein by Western blot. In liver, muscle and placenta, IGF-I mRNA and protein levels were reduced by between 8 and 30% in IGF-I-treated fetuses compared with saline-treated fetuses and controls with no change in IGF-1R mRNA or protein levels. In contrast, in the gut, IGF-I mRNA and protein levels were not significantly altered with IGF-I treatment, but IGF-1R levels were increased, especially in the jejunum. Immunolocalisation demonstrated that IGF-1R expression was confined to the luminal aspect of the gut. mRNA levels of all three IGFBPs were reduced in the gut of IGF-I-treated fetuses, but hepatic expression was significantly increased. These data demonstrated tissue-specific regulation of IGF-I, IGF-1R and IGFBPs-1, -2 and -3 in response to intra-amniotic IGF-I supplementation, though the underlying mechanisms remain obscure.

Circulating insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs) and tissue mRNA levels of IGFBP-2 and IGFBP-4 in the ovine fetus

1995 ◽  
Vol 145 (3) ◽  
pp. 545-557 ◽  
Author(s):  
J M Carr ◽  
J A Owens ◽  
P A Grant ◽  
P E Walton ◽  
P C Owens ◽  
...  
Keyword(s):  
Binding Proteins ◽  
Mrna Level ◽  
Common Factor ◽  
Late Gestation ◽  
Mrna Levels ◽  
Igf Binding Proteins ◽  
Fetal Sheep ◽  
Igf I ◽  
Igf Binding ◽  
Igfbp 3

Abstract The IGF-binding proteins (IGFBPs) are a family of at least six structurally related proteins, which bind the IGFs and modulate their actions, including the regulation of preand postnatal growth. In this study we have examined the relationship between circulating and tissue mRNA levels of IGFBPs and related this to circulating IGFs in the fetal sheep over the gestational period when rapid growth and development occurs. Circulating IGFBP-2, as measured by Western ligand blot (WLB), increases between early and mid gestation, remains high, then declines throughout late gestation (P=0·0002). Circulating IGFBP-3 increases throughout gestation, as measured by WLB or RIA (P=0·04 and P=0·0001 respectively), as does circulating IGFBP-4 (P=0·004). These ontogenic changes in circulating IGFBPs-2 and -4 are paralleled by changes in liver mRNA for these proteins and, for IGFBP-2, by those in kidney IGFBP-2 mRNA also. This suggests that liver and kidney may be the primary contributors to circulating IGFBP-2 and the liver to circulating IGFBP-4. IGFBP-2 mRNA is present in the heart and lung in early gestation but barely detectable in these tissues after approximately 60 days gestation. IGFBP-4 mRNA is also present in the heart in early but not late gestation, but is abundant in the lung throughout gestation. These results demonstrate tissue specific and developmental regulation of IGFBPs-2 and -4 at the mRNA level. To assess any role the circulating IGFs may play in mediating these changes in IGFBPs, or vice versa, both plasma IGF-I and IGF-II were measured by RIA. Circulating IGF-I increases as gestation progresses (P=0·0001), while circulating IGF-II increases between early and mid gestation, remains high (P=0·01), then declines. Circulating IGF-I is positively correlated with fetal weight (r=0·66, P=0·03), circulating IGFBP-3 (r=0·54, P=0·01) and IGFBP-4 (r=0·52, P=0·01). Circulating IGF-II positively correlates with circulating IGFBP-2 (r=0·48, P=0·02) throughout gestation and at 1 day postnatally. These relationships are consistent with circulating IGF-I influencing IGFBPs-3 and -4, and similarly, IGF-II determining IGFBP-2, or vice versa. Alternatively, these correlations may reflect coordinate regulation of IGF and IGFBP by a common factor. Journal of Endocrinology (1995) 145, 545–557

Developmental changes in the expression patterns of IGFs, type 1 IGF receptor and IGF-binding proteins-2 and -4 in perinatal rat lung

1995 ◽  
Vol 15 (2) ◽  
pp. 105-115 ◽  
Author(s):  
D C Batchelor ◽  
A-M Hutchins ◽  
M Klempt ◽  
S J M Skinner
Keyword(s):  
Binding Proteins ◽  
Mrna Levels ◽  
Rat Lung ◽  
Igf Binding Proteins ◽  
Igf System ◽  
Igf I ◽  
Igf Binding ◽  
Igf Receptor ◽  
Specific Regulation

ABSTRACT The insulin-like growth factors (IGF-I and IGF-II), their receptors and binding proteins (IGFBPs) are endogenously expressed in a number of tissues including the lung during fetal and neonatal development. This endogenous autocrine/paracrine IGF 'system', together with endocrine sources, contributes to the regulation of lung cell proliferation. We investigated the expression of the mRNAs encoding IGF-I, IGF-II, the type 1 IGF receptor (IGF-T1R) and two IGF-binding proteins (IGFBP-2 and IGFBP-4) in rat lung during the perinatum. These were compared in lung with surfactant apoprotein A (Sp-A) mRNA levels. mRNA in extracts of fetal tissues collected between day 17 of gestation (17f) and day 9 after birth (9d) was estimated by Northern blot or RNase protection analysis. At day 20 of gestation IGF-I, IGF-T1R and IGFBP-4 mRNA levels were higher in lung than liver (all P<0·01), whereas IGF-II and IGFBP-2 mRNA levels were higher in liver than lung (each P<0·02). The expression of IGF-I, IGFBP-2 and IGFBP-4 in lung was high before birth (days 17–20f) but decreased to low levels at days 21f, 22f or at birth (1d) but increased in the neonatal lung. IGF-II expression in lung was high at 17f but decreased before birth and remained low after birth. The IGF-T1R was expressed at moderate levels before birth, decreased before birth but peaked at days 2–5 after birth. The decrease in expression of these growth regulators before birth was matched by an increase in Sp-A expression which was clearly seen at day 20f, peaked at 1d and then was maintained at high levels after birth. Primary cell cultures of 18f lung epithelia express IGFBP-2 while fibroblasts from the same animals express only IGFBP-4. Cells grown from 22f lung tissue express IGFBP-2 and IGFBP-4 at lower levels, behaving in vitro as they do in vivo. The contrasting levels of expression of different components of the IGF system in the fetal lung and liver indicate organ-specific regulation. IGFBP-2 and IGFBP-4 expression in different cell types within lung but with similar temporal changes suggests cell-specific regulation, perhaps by a common agent. The patterns of expression of IGF-I, IGF-T1R, IGFBP-2 and IGFBP-4, but not IGF-II, in developing lung correspond to previously described phasic changes in lung cell proliferation rates. The nadir in expression of these four major components of the lung IGF system occurs in the saccular phase when the lung begins to differentiate, probably under the influence of certain endocrine agents.

Glucose regulation of the IGF response system in chondrocytes: induction of an IGF-I-resistant state

1999 ◽  
Vol 276 (4) ◽  
pp. R1164-R1171 ◽  
Author(s):  
K. M. Kelley ◽  
T. R. Johnson ◽  
J. Ilan ◽  
R. W. Moskowitz
Keyword(s):  
Glucose Concentration ◽  
Northern Analysis ◽  
Type I ◽  
Mrna Levels ◽  
Protein Levels ◽  
Receptor Mrna ◽  
Response System ◽  
Type I Igf Receptor ◽  
Igf I ◽  
Igf Receptor

Nonresponsiveness to the growth-stimulatory actions of insulin-like growth factor (IGF)-I in chondrocytes has been reported in a number of disease states associated with impaired glucose metabolism. Primary rabbit chondrocytes were investigated for changes in their IGF response system [type-I IGF receptor and IGF-binding protein (IGFBP) expression] and in their ability to mount a synthetic response to IGF-I [as35S-labeled proteoglycan ([35S]PG) production] in media containing varying ambient glucose concentrations. Whereas basal [35S]PG synthetic rate was unaffected by glucose concentration, synthetic responsiveness to IGF-I was lost in media containing <5 mmol/l glucose or in media containing a “diabetic” glucose concentration (25 mmol/l). IGFBP expression, as measured by Northern analysis of mRNA levels and Western ligand blotting of secreted protein levels, was not significantly altered in the different glucose media, nor were there any differences in the cell surface localization of IGFBPs as assessed by affinity cross-linking with 125I-labeled IGF-I, suggesting that IGFBPs do not induce the IGF-I resistance. The nonresponsiveness to IGF-I in reduced glucose occurred with 25–50% reductions in steady-state levels of IGF type-I receptor mRNA and protein. A significant correlation between IGF receptor mRNA level and synthetic response to IGF-I was observed between 0 and 10 mmol/l glucose concentrations, suggesting that the loss of responsiveness in reduced glucose is manifested at the level of transcription and/or receptor mRNA stability. In contrast, nonresponsiveness to IGF-I in chondrocytes in diabetic glucose concentrations occurred without changes in receptor mRNA and protein levels, suggesting that IGF-I resistance was due to post-ligand-binding receptor defects. It is proposed that IGF-I resistance in chondrocytes subjected to inappropriate glucose levels may constitute an important pathogenic mechanism in degenerative cartilage disorders.

scholarly journals Insulin-like Growth Factor II Signaling in Neoplastic Proliferation Is Blocked by Transgenic Expression of the Metalloproteinase Inhibitor Timp-1

1999 ◽  
Vol 146 (4) ◽  
pp. 881-892 ◽  
Author(s):  
David C. Martin ◽  
John L. Fowlkes ◽  
Bojana Babic ◽  
Rama Khokha
Keyword(s):  
Growth Factor ◽  
T Antigen ◽  
Tissue Inhibitor Of Metalloproteinase ◽  
Early Event ◽  
Mrna Levels ◽  
Insulin Like Growth Factor ◽  
Igf Binding Proteins ◽  
Protein Levels ◽  
Igf I ◽  
Igfbp 3

Insulin-like growth factor (IGF) II is overexpressed in many human cancers and is reactivated by, and crucial for viral oncogene (SV40 T antigen, [TAg])–induced tumorigenesis in several tumor models. Using a double transgenic murine hepatic tumor model, we demonstrate that tissue inhibitor of metalloproteinase 1 (TIMP-1) blocks liver hyperplasia during tumor development, despite TAg-mediated reactivation of IGF-II. Because the activity of IGFs is controlled by IGF-binding proteins (IGFBPs), we investigated whether TIMP-1 overexpression altered the IGFBP status in the transgenic liver. Ligand blotting showed that IGFBP-3 protein levels were increased in TIMP-1–overexpressing double transgenic littermates, whereas IGFBP-3 mRNA levels were not different, suggesting that TIMP-1 affects IGFBP-3 at a posttranscriptional level. IGFBP-3 proteolysis assays demonstrated that IGFBP-3 degradation was lower in TIMP-1–overexpressing livers, and zymography showed that matrix metalloproteinases (MMPs) were present in the liver homogenates and were capable of degrading IGFBP-3. As a consequence of reduced IGFBP-3 proteolysis and elevated IGFBP-3 protein levels, dissociable IGF-II levels were significantly lower in TIMP-1–overexpressing animals. This decrease in bioavailable IGF-II ultimately resulted in diminished IGF-I receptor signaling in vivo as evidenced by diminished receptor kinase activity and decreased tyrosine phosphorylation of the IGF-I receptor downstream effectors, insulin receptor substrate 1 (IRS-1), extracellular signal regulatory kinase (Erk)-1, and Erk-2. Together, these results provide evidence that TIMP-1 inhibits liver hyperplasia, an early event in TAg-mediated tumorigenesis, by reducing the activity of the tumor-inducing mitogen, IGF-II. These data implicate the control of MMP-mediated degradation of IGFBPs as a novel therapy for controlling IGF bioavailability in cancer.

scholarly journals Zinc partitions IGFs from soluble IGF binding proteins (IGFBP)-5, but not soluble IGFBP-4, to myoblast IGF type 1 receptors

2004 ◽  
Vol 180 (2) ◽  
pp. 227-246 ◽  
Author(s):  
RH McCusker ◽  
J Novakofski
Keyword(s):  
Cell Surface ◽  
Binding Sites ◽  
Affinity Binding ◽  
Igf Binding Proteins ◽  
Igf I ◽  
Igf Binding ◽  
Igf Receptor ◽  
Igf Binding Protein

Zinc (Zn(2+)), a multifunctional micronutrient, was recently shown to lower the affinity of cell-associated insulin-like growth factor (IGF) binding protein (IGFBP)-3 and IGFBP-5 for both IGF-I and IGF-II, but to increase the affinity of the cell surface type 1 IGF receptor (IGF-1R) for the same two ligands. However, there is a need for data concerning the effects of Zn(2+) on soluble IGFBPs and the type 2 IGF receptor (IGF-2R). In the current work, we demonstrate that Zn(2+) affects the affinity of IGFBP-5 secreted by myoblasts but not IGFBP-4. Zn(2+), at physiological levels, depressed binding of both IGF-I and IGF-II to IGFBP-5, affecting (125)I-IGF-I more than (125)I-IGF-II. Both (125)I-IGF-I and (125)I-IGF-II bound to high and low affinity sites on IGFBP-5. Zn(2+) converted the high affinity binding sites of IGFBP-5 into low affinity binding sites. An IGF-I analog, (125)I-R(3)-IGF-I, did not bind to the soluble murine IGFBP-5. Zn(2+) also decreased the affinity of the IGF-2R on L6 myoblasts. In contrast, Zn(2+) increased IGF-I, IGF-II and R(3)-IGF-I binding to the IGF-1R by increasing ligand binding affinity on both P(2)A(2a)-LISN and L6 myoblasts. Soluble IGFBP-5 and IGFBP-4 depressed the binding of (125)I-IGF-I and (125)I-IGF-II to the IGF-1R, but did not affect binding of (125)I-R(3)-IGF-I. By depressing the association of the IGFs with soluble IGFBP-5, Zn(2+) partitioned (125)I-IGF-I and (125)I-IGF-II from soluble IGFBP-5 onto cell surface IGF-1Rs. This effect is not seen when soluble L6-derived IGFBP-4 is present in extracellular fluids. We introduce a novel mechanism by which the trace micronutrient Zn(2+) may alter IGF distribution, i.e. Zn(2+) acts to increase IGF-1R binding at the expense of IGF binding to soluble IGFBP-5 and the IGF-2R.

scholarly journals IGF-I stimulates chemotaxis of human neuroblasts. Involvement of type 1 IGF receptor, IGF binding proteins, phosphatidylinositol-3 kinase pathway and plasmin system

2000 ◽  
Vol 165 (1) ◽  
pp. 123-131 ◽  
Author(s):  
A Puglianiello ◽  
D Germani ◽  
P Rossi ◽  
S Cianfarani
Keyword(s):  
Cell Migration ◽  
Cell Motility ◽  
Igf Binding Proteins ◽  
Neuroblast Migration ◽  
Igf I ◽  
Igf Binding ◽  
Igf Receptor ◽  
Kinase Pathway

SH-SY5Y human neuroblastoma cells express IGF receptors, IGFs and IGF binding proteins (IGFBPs), and provide a model for studying the role of the IGF system in human neuronal development. We investigated the effect of IGF-I and des(1-3)IGF-I on the motility of SH-SY5Y cells by a cell migration assay based on the assessment of the number of cells which migrated across 8 microm pore size membranes and around an agarose drop. IGF-I and des(1-3)IGF-I stimulated neuroblast chemotaxis in a dose-dependent manner. Treatment of cells with these agents for 24 h resulted in a significant increase (IGF-I by 70% and des(1-3)IGF-I by 90%; P<0. 0001) in cell motility relative to control conditions. Addition of monoclonal antibody against type 1 IGF receptor (alpha-IR3), significantly (P<0.05) reduced the cell motility induced by IGF-I (by 30%) and des(1-3)IGF-I (by 70%). Wortmannin, a specific inhibitor of phosphatidylinositol (PI)-3 kinase intracellular signalling, also reduced the IGF-stimulated cell migration (by over 40%, P<0.01), indicating a key role of the PI-3 kinase pathway in mediating the IGF effect on neuroblast migration. Finally, cell treatment with plasminogen (PLG) markedly enhanced neuroblast migration (by over 200%, P<0.01), whereas incubation with the PLG inhibitor 4-(2-aminoethyl)-benzenesulphonyl fluoride reduced cell motility (by 80%, P<0.01), thus suggesting an involvement of PLG-dependent IGFBP proteolysis in the regulation of neuroblast motility. In conclusion, IGF-I is a potent stimulator of neuroblast migration through the activation of type 1 IGF receptor and the PI-3 kinase intracellular pathway. IGFBPs and the plasmin system seem to play a role in cell motility, although the nature and the extent of their involvement has yet to be elucidated.

Ontogeny and effect of cortisol on vasopressin-1b receptor expression in anterior pituitaries of fetal sheep

2003 ◽  
Vol 284 (1) ◽  
pp. R51-R56 ◽  
Author(s):  
Sharla F. Young ◽  
Jennifer L. Smith ◽  
Jorge P. Figueroa ◽  
James C. Rose
Keyword(s):  
Receptor Expression ◽  
Late Gestation ◽  
Mrna Levels ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Protein Levels ◽  
Receptor Mrna ◽  
Naturally Occurring ◽  
V1b Receptor

Corticotroph responsiveness to arginine vasopressin (AVP) increases during late gestation in fetal sheep. The mechanism of this increase in AVP responsiveness is currently unknown but could be related to an increase in vasopressin type 1b (V1b) receptor expression in the pituitary during development. To determine if there are ontogenic changes in V1b receptor expression that may help explain the changes in ACTH responses to AVP, we studied pituitaries from three groups of fetal sheep [100, 120, or 140 days gestational age (dGA)]. V1b receptor mRNA and protein significantly decreased by 140 dGA. Peak V1b mRNA levels were detected at 100 dGA, while peak V1b protein levels were detected at 120 dGA. The reduction in V1b receptor expression in late gestation may be due to the naturally occurring peripartum increase in fetal plasma cortisol because cortisol infusion at 122–130 dGA decreased V1b receptor mRNA. Thus there is a marked decrease in the expression of the V1b receptor in the pituitary during fetal development, leaving the role of the V1b receptor in increasing AVP responsiveness uncertain.

Hypothalamic-pituitary disconnection in fetal sheep blocks the peripartum increases in adrenal responsiveness and adrenal ACTH receptor expression

2005 ◽  
Vol 289 (2) ◽  
pp. R410-R417 ◽  
Author(s):  
Nancy K. Valego ◽  
Yixin Su ◽  
Luke C. Carey ◽  
Sharla F. Young ◽  
Stephen B. Tatter ◽  
...  
Keyword(s):  
Plasma Cortisol ◽  
Receptor Expression ◽  
Late Gestation ◽  
Mrna Levels ◽  
Acth Stimulation ◽  
Fetal Sheep ◽  
Protein Levels ◽  
Overnight Incubation ◽  
Acth Receptor ◽  
Underlying Mechanisms

Although it has been recognized for over a decade that hypothalamic-pituitary disconnection (HPD) in fetal sheep prevents the late gestation rise in plasma cortisol concentrations, the underlying mechanisms remain unclear. We hypothesized that reductions in adrenal responsiveness and ACTH receptor (ACTH-R) expression may be mediating factors. HPD or sham surgery was performed at 120 days of gestation, and catheters were placed for blood sampling. At ∼138 days of gestation, fetuses were killed, and adrenals were removed for cell culture and analyses of ACTH-R mRNA and protein. After 48 h, adrenocortical cells were stimulated with ACTH for 2 h, and the medium was collected for cortisol measurement. The same cells were incubated overnight with medium or medium containing ACTH or forskolin (FSK), followed by ACTH stimulation (as above) and cortisol and cellular ACTH-R mRNA analyses. HPD prevented the late gestation increase in plasma cortisol and bioactive ACTH and reduced adrenal ACTH-R mRNA and protein levels by over 35%. HPD cells secreted significantly less cortisol than sham cells (3.2 ± 1.2 vs. 47.3 ± 11.1 ng·ml−1·2 h−1) after the initial ACTH stimulation. Overnight incubation of HPD cells with ACTH or FSK restored cortisol responses to acute stimulation to levels seen in sham cells initially. ACTH-R mRNA levels in cells isolated from HPD fetuses were decreased by over 60%, whereas overnight incubation with ACTH or FSK increased levels by approximately twofold. Our findings indicate that the absence of the cortisol surge in HPD fetuses is a consequence, at least in part, of decreased ACTH-R expression and adrenal responsiveness.

Insulin-like growth factor axis in airway smooth muscle cells

1994 ◽  
Vol 267 (6) ◽  
pp. L761-L765 ◽  
Author(s):  
J. P. Noveral ◽  
A. Bhala ◽  
R. L. Hintz ◽  
M. M. Grunstein ◽  
P. Cohen
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Airway Smooth Muscle Cells ◽  
Igf Binding Proteins ◽  
Cell Proliferation And Differentiation ◽  
Igf Receptors ◽  
Igf I ◽  
Igf Receptor ◽  
Mediate Cell

Insulin-like growth factors (IGFs) mediate cell proliferation and differentiation and bind with high affinities and specificities to IGF receptors and IGF-binding proteins (IGFBPs). We examined the roles of these three groups of proteins in cultured rabbit airway smooth muscle (ASM) cells. Affinity cross-linking of IGF-I and IGF-II to membranes of ASM cells revealed type 1 and type 2 IGF receptors. Western ligand blot analysis of ASM cell-conditioned medium revealed the presence of a single IGFBP band that precipitated with an antibody specific to IGFBP-2. ASM cells secreted radioimmunoassayable IGF-II; however, no IGF-I was detected under the same conditions. Two molecular weight forms of IGF-II were produced by the ASM cells. Exposure of cells to 1,000 ng/ml of IGF-I stimulated them to proliferate to 230 +/- 9.7% of their respective controls. Exposure to 1,000 ng/ml of IGF-II was approximately 40% as effective as exposure to 1,000 ng/ml of IGF-I. Both IGF-I and IGF-II exhibited binding to the type 1 IGF receptor. In summary, IGFs are mitogens for cultured rabbit ASM cells, and their actions are most likely mediated through the type 1 IGF receptor. The ASM cells secrete IGF-II and IGFBP-2, and the latter could modulate the actions of the IGFs in these cells.

Characterization of serum-derived and recombinant rat IGF-I and their use for measuring true concentrations of IGF-I in rat plasma

1996 ◽  
Vol 149 (3) ◽  
pp. 379-387 ◽  
Author(s):  
Z Upton ◽  
H Webb ◽  
F M Tomas ◽  
F J Ballard ◽  
G L Francis
Keyword(s):  
Rat Plasma ◽  
Reference Standards ◽  
Igf Binding Proteins ◽  
Igf I ◽  
Igf Binding ◽  
Igf Receptor

Abstract While numerous researchers have used rat models to investigate the in vivo actions of IGF-I, interpretation of the results in terms of true concentrations of rat IGF-I (rIGF-I) in plasma has been hampered by the absence of homologous reference standards. In order to overcome this we have produced recombinant rIGF-I (rrIGF-I) from Escherichia coli using procedures similar to those we have previously described for the production of other recombinant IGFs. The rrIGF-I is indistinguishable from serum-derived rIGF-I when characterized in a number of in vitro assays including ability to stimulate protein synthesis and inhibit protein degradation in cultured rat cells, as well as in interactions with the rat type-1 IGF receptor and with rat IGF-binding proteins. Moreover, both the serum-derived and the recombinant rat proteins are similar to recombinant human IGF-I (rhIGF-I) in these assays. However, differences between the human and rat IGFs are apparent when tested in immunoassays using some antibodies raised against rhIGF-I. Furthermore, the differences between rhIGF-I and rrIGF-I are even greater when rhIGF-I is used as the competing radiolabel in these assays, a situation that can lead to a two- to threefold underestimation of the actual concentration of IGF-I in rat plasma. These results indicate that, while immunoassays employing antibodies raised against rhIGF-I and rhIGF-I reference standards reliably indicate trends in IGF-I concentrations in rat plasma, the true amounts of rIGF-I present can only be assured in an assay using homologous tracer and reference peptides. Journal of Endocrinology (1996) 149, 379–387

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