Recombinant Insulin-like Growth factor-I Research Articles

Modification of Carp (Osphronemus Gouramy) Growth with Insulin-Like Growth Factor-I Recombinant Mouse in Vivo

Osphronemus gouramy consumption is increasing every year, which causes a high number of inquiries for this fish, which cannot be offset sufficiently by the amount of production. The growth rate of O. gouramy is relatively slow, so achieving the required consumption is relatively long. Quality improvement of productivity by improving the ability of cell metabolism to intake fish feed through hormone injection recombinant mouse insulin-like growth factor-I (IGF-I) is expected to spur growth so that fish production can be increased. This study aims to determine the effect of the hormone IGF-I recombinant mouse on the increased growth of O. gouramy. The benefits of this research are expected to deliver the benefits of science in the form of scientific information to the public in general and fish farmers, especially about the effect of the hormone recombinant mouse IGF-I on the growth of O. gouramy. The research method is carried out experimentally by using a completely randomized design (RAL); this study uses 80 O. gouramy was divided into 4 treatments P0: without hormone injections of IGF-I, P1: injected with the hormone IGF-I at a dose of 10 ng/ml, P2: injected with the hormone IGF-I at a dose of 20 ng/ml and P3: injected with the hormone at a dose of 40 ng/ml each of 5 replicates each test 4 tail O. gouramy. The hormone IGF-I recombinant mouse is done by injection. The treatment with hormone injection of recombinant mouse IGF-I. The parameters measured were growth. The results showed that the treatment hormone injection of recombinant mouse IGF-I with different doses gave significant differences (p <0.05); weight growth (P0: 0 ng/ml = 7,23 gram ± 0,37-gram dan P3: 40 ng/ml = 26,35 gram ± 1,89 gram.); length growth (P0 : 0 ng/ml = 5,76 cm ± 0,38 cm dan P3: 40 ng/ml = 7,93 cm ± 0,07 cm). The conclusion is that recombinant mouse IGF-I increased the growth by increasing in weight and length of O. gouramy, and improvement of the growth occurred in the treatment injection of the dose: 40 ng/ml.

Essential Amino Acid Intake Is Required for Sustaining Serum Insulin-like Growth Factor-I Levels but Is Not Necessarily Needed for Body Growth.

Essential amino acids (EAAs) are those that cannot be synthesized enough to meet organismal demand; therefore, it is believed that they must be taken from the diet for optimal growth. The growth hormone (GH)/insulin-like growth factor-I (IGF-I) system is also considered significant for growth regulation in mammals. This study aimed to evaluate the relative contributions of protein nutrition and the GH/IGF-I system to body growth regulation. Experiments using rodents and hepatocyte-derived cell lines subjected to EAA deficiency showed that a reduction in the serum EAA concentration hinders Igf1 transcription in the liver in a cell-autonomous manner, thereby decreasing serum IGF-I levels. Remarkably, when the serum IGF-I level of mice on a low-protein diet was restored by the recombinant IGF-I infusion, the body growth was mostly rescued, although the mice were still deficient in EAA intake. Meanwhile, the GH signal activation and subsequent Igf1 transcription were also dramatically diminished by EAA deprivation in the cell culture model. Altogether, we demonstrate that EAAs are not strictly necessary for animal growth as building blocks but are required as IGF-I-tropic cues. The results will bring a paradigm shift regarding the definition of “essential” amino acids.

Mechanism study of dendritic epidermal T lymphocytes in promoting healing of full-thickness skin defects wound on mice by regulating the proliferation and differentiation of epidermal stem cells in mice

Mechanism study of dendritic epidermal T lymphocytes in promoting healing of full-thickness skin defects wound on mice by regulating the proliferation and differentiation of epidermal stem cells in mice

Effects of skin γδ T lymphocytes on wound healing of mice through regulating proliferation and differentiation of mice epidermal cells

Effects of skin γδ T lymphocytes on wound healing of mice through regulating proliferation and differentiation of mice epidermal cells

Potency of Full-Length MGF to Induce Maximal Activation of the IGF-I R Is Similar to Recombinant Human IGF-I at High Equimolar Concentrations.

AimsTo compare full-length mechano growth factor (full-length MGF) with human recombinant insulin-like growth factor-I (IGF-I) and human recombinant insulin (HI) in their ability to activate the human IGF-I receptor (IGF-IR), the human insulin receptor (IR-A) and the human insulin receptor-B (IR-B), respectively. In addition, we tested the stimulatory activity of human MGF and its stabilized analog Goldspink-MGF on the IGF-IR.MethodsThe effects of full-length MGF, IGF-I, human mechano growth factor (MGF), Goldspink-MGF and HI were compared using kinase specific receptor activation (KIRA) bioassays specific for IGF-I, IR-A or IR-B, respectively. These assays quantify activity by measuring auto-phosphorylation of the receptor upon ligand binding.ResultsIGF-IR: At high equimolar concentrations maximal IGF-IR stimulating effects generated by full-length MGF were similar to that of IGF-I (89-fold vs. 77-fold, respectively). However, EC50 values of IGF-I and full-length MGF for the IGF-I receptor were 0.86 nmol/L (95% CI 0.69–1.07) and 7.83 nmol/L (95% CI: 4.87–12.58), respectively. No IGF-IR activation was observed by human MGF and Goldspink-MGF, respectively. IR-A/IR-B: At high equimolar concentrations similar maximal IR-A stimulating effects were observed for full -length MGF and HI, but maximal IR-B stimulation achieved by full -length MGF was stronger than that by HI (292-fold vs. 98-fold). EC50 values of HI and full-length MGF for the IR-A were 1.13 nmol/L (95% CI 0.69–1.84) and 73.11 nmol/L (42.87–124.69), respectively; for IR-B these values were 1.28 nmol/L (95% CI 0.64–2.57) and 35.10 nmol/L (95% 17.52–70.33), respectively.ConclusionsFull-length MGF directly stimulates the IGF-IR. Despite a higher EC50 concentration, at high equimolar concentrations full-length MGF showed a similar maximal potency to activate the IGF-IR as compared to IGF-I. Further research is needed to understand the actions of full-length MGF in vivo and to define the physiological relevance of our in vitro findings.

Insulin-Like Growth Factor I Inhibits Alveolar Bone Loss Following Tooth Extraction in Rats.

Alveolar bone is often lost after tooth extraction. Few studies have assessed the longitudinal changes in bone volume that occur within these extraction sites. To investigate the longitudinal morphological changes in extraction sockets following sustained continuous subcutaneous infusion of human recombinant insulin-like growth factor I (IGF-I). Fourteen rats were subjected to right mandibular first molar extraction. Experimental rats (n = 7) received a continuous subcutaneous infusion of human recombinant IGF-I (320 mg/day) for 3 weeks by osmotic minipump. Control animals were treated with saline via the same method (n = 7). All rats were then housed for an additional 3 weeks. Micro-CT scanning was performed immediately after tooth extraction and at 1, 2, 3, and 6 weeks after extraction. New bone formation was markedly higher in the IGF-I-treated group as compared with the control group. The loss in alveolar ridge height in the IGF-I group was significantly lower than that in the control group at each time point after extraction on the buccal side and at 2, 3, and 6 weeks on the lingual side. IGF-I treatment increases the volume of newly formed bone and reduces the loss in alveolar ridge height following tooth extraction.

Endogenous versus exogenous growth factor regulation of articular chondrocytes

Anabolic growth factors that regulate the function of articular chondrocytes are candidates for articular cartilage repair. Such factors may be delivered by pharmacotherapy in the form of exogenous proteins, or by gene therapy as endogenous proteins. It is unknown whether delivery method influences growth factor effectiveness in regulating articular chondrocyte reparative functions. We treated adult bovine articular chondrocytes with exogenous recombinant insulin-like growth factor-I (IGF-I) and transforming growth factor-beta1 (TGF-β1), or with the genes encoding these growth factors for endogenous production. Treatment effects were measured as change in chondrocyte DNA content, glycosaminoglycan production, and aggrecan gene expression. We found that IGF-I stimulated chondrocyte biosynthesis similarly when delivered by either exogenous or endogenous means. In contrast, exogenous TGF-β1 stimulated these reparative functions, while endogenous TGF-β1 had little effect. Endogenous TGF-β1 became more bioactive following activation of the transgene protein product. These data indicate that effective mechanisms of growth factor delivery for articular cartilage repair may differ for different growth factors. In the case of IGF-I, gene therapy or protein therapy appear to be viable options. In contrast, TGF-β1 gene therapy may be constrained by a limited ability of chondrocytes to convert latent complexes to an active form.

In Vitro and In Vivo Effects of IGF-I on Adiposity in HIV-associated Metabolic Disease: A Pilot Study

We tested the effects of recombinant insulin-like growth factor-I (IGF-I) in an adipocyte model of HIV lipodystrophy and in an open label study on body composition and metabolism in patients with HIV lipodystrophy. The effects of IGF-I on ritonavir-induced adipocyte cell death were studied in vitro. We assessed lipid accumulation, IGF signaling, apoptosis, and gene expression. We conducted a 24-week open label trial of recombinant IGF-I in ten adults with HIV associated lipoatrophy. Laboratory assessments included glucose, insulin, lipids, and IGF-I. At weeks 0 and 24, body composition studies were performed including skinfold measurement, dual-energy x-ray absorptiometry, and computed tomography of the abdomen and thigh. In vitro, ritonavir increased delipidation and apoptosis of adipocytes, whereas co-treatment with IGF-I attenuated the effect. In the clinical study, subcutaneous adipose tissue did not increase in patients after treatment with IGF-I; however, there was a decrease in the proportion of abdominal fat (39.8 ± 7% vs. 34.6 ± 7%, p = 0.007). IGF-I levels increased with treatment (143 ± 28 μg/L at week 0 vs. 453 ± 212 μg/L at week 24, p = 0.002), whereas IGFBP-3 levels declined (3.554 ± 1.146 mg/L vs. 3.235 ± 1.151 mg/L, p = 0.02). Insulin at week 12 decreased significantly (90.1 ± 39.8 pmol/L vs. 33.2 ± 19.6 pmol/L, p = 0.002). There was a nonsignificant decrease in visceral adipose tissue (155.2 ± 68 cm² at week 0 vs. 140.6 ± 70 cm² at week 24, p = 0.08). Use of recombinant IGF-I may lower fasting insulin and abdominal fat in patients with lipoatrophy associated with HIV infection. Further evaluation of this agent for treatment of HIV-associated lipodystrophy may be warranted.

Insulin-like growth factor-I stimulates differentiation of ATII cells to ATI-like cells through activation of Wnt5a

Alveolar type II (ATII) epithelial cells play a crucial role in the repair and remodeling of the lung following injury. ATII cells have the capability to proliferate and differentiate into alveolar type I (ATI) cells in vivo and into an ATI-like phenotype in vitro. While previous reports indicate that the differentiation of ATII cells into ATI cells is a complex biological process, the underlying mechanism responsible for differentiation is not fully understood. To investigate factors involved in this differentiation in culture, we used a PCR array and identified several genes that were either up- or downregulated in ATI-like cells (day 6 in culture) compared with day 2 ATII cells. Insulin-like growth factor-I (IGF-I) mRNA was increased nearly eightfold. We found that IGF-I was increased in the culture media of ATI-like cells and demonstrated a significant role in the differentiation process. Treatment of ATII cells with recombinant IGF-I accelerated the differentiation process, and this effect was abrogated by the IGF-I receptor blocker PQ401. We found that Wnt5a, a member of the Wnt-Frizzled pathway, was activated during IGF-I-mediated differentiation. Both protein kinase C and β-catenin were transiently activated during transdifferentiation. Knocking down Wnt5a using small-interfering RNA abrogated the differentiation process as indicated by changes in the expression of an ATII cell marker (prosurfactant protein-C). Treatment of wounded cells with either IGF-I or Wnt5a stimulated wound closure. These results suggest that IGF-I promotes differentiation of ATII to ATI cells through the activation of a noncanonical Wnt pathway.

Local administration of insulin‐like growth factor‐I(IGF‐I) stimulates tendon collagen synthesis in humans

Collagen is the predominant structural protein in tendons and ligaments, and can be controlled by hormonal changes. In animals, injections of insulin-like growth factor I (IGF-I) has been shown to increase collagen synthesis in tendons and ligaments and to improve structural tissue healing, but the effect of local IGF-I administration on tendon collagen synthesis in human has not been studied. The purpose of this study was to study whether local injections of IGF-I would have a stimulating effect on tendon collagen synthesis. Twelve healthy nonsmoking men [age 62 ± 1 years (mean ± SEM), BMI 27 ± 1] participated. Two injections of either human recombinant IGF-I (0.1 mL Increlex©) or saline (control) into each patellar tendon were performed 24-h apart, respectively. Tendon collagen fractional synthesis rate (FSR) was measured by stable isotope technique in the hours after the second injection. Simultaneously, interstitial peritendinous (IGF-I) and [procollagen type I N-terminal propeptide (PINP)], as a marker for type I collagen synthesis, were determined by microdialysis technique. Tendon collagen FSR and PINP were significantly higher in the IGF-I leg compared with the control leg (P < 0.05). In conclusion, local IGF-I administration can directly enhance tendon collagen synthesis both within and around the human tendon tissue.

Nutrition and chronic kidney disease

The incidence of malnutrition disorders in chronic kidney disease (CKD) appears unchanged over time, whereas patient-care and dialysis techniques continue to progress. Despite some evidence for cost-effective treatments, there are numerous caveats to applying these research findings on a daily care basis. There is a sustained generation of data confirming metabolic improvement when patients control their protein intake, even at early stages of CKD. A recent protein-energy wasting nomenclature allows a simpler approach to the diagnosis and causes of malnutrition. During maintenance dialysis, optimal protein and energy intakes have been recently challenged, and there is no longer an indication to control hyperphosphatemia through diet restriction. Recent measurements of energy expenditure in dialysis patients confirm very low physical activity, which affects energy requirements. Finally, inflammation, a common state during CKD, acts on both nutrient intake and catabolism, but is not a contraindication to a nutritional intervention, as patients do respond and improve their survival as well as do noninflamed patients.

Alanine Scanning of a Putative Receptor Binding Surface of Insulin-like Growth Factor-I

Current evidence supports a binding model in which the insulin molecule contains two binding surfaces, site 1 and site 2, which contact the two halves of the insulin receptor. The interaction of these two surfaces with the insulin receptor results in a high affinity cross-linking of the two receptor alpha subunits and leads to receptor activation. Evidence suggests that insulin-like growth factor-I (IGF-I) may activate the IGF-I receptor in a similar mode. So far IGF-I residues structurally corresponding to the residues of the insulin site 1 together with residues in the C-domain of IGF-I have been found to be important for binding of IGF-I to the IGF-I receptor (e.g. Phe(23), Tyr(24), Tyr(31), Arg(36), Arg(37), Val(44), Tyr(60), and Ala(62)). However, an IGF-I second binding surface similar to site 2 of insulin has not been identified yet. In this study, we have analyzed whether IGF-I residues corresponding to the six residues of the insulin site 2 have a role in high affinity binding of IGF-I to the IGF-I receptor. Six single-substituted IGF-I analogues were produced, each containing an alanine substitution in one of the following positions (corresponding insulin residues in parentheses): Glu(9) (His(B10)), Asp(12) (Glu(B13)), Phe(16) (Leu(B17)), Asp(53) (Ser(A12)), Leu(54) (Leu(A13)), and Glu(58) (Glu(A17)). In addition, two analogues with 2 and 3 combined alanine substitutions were also produced (E9A,D12A IGF-I and E9A,D12A,E58A IGF-I). The results show that introducing alanine in positions Glu(9), Asp(12), Phe(16), Leu(54), and Glu(58) results in a significant reduction in IGF-I receptor binding affinity, whereas alanine substitution at position 53 had no effect on IGF-I receptor binding. The multiple substitutions resulted in a 33-100-fold reduction in IGF-I receptor binding affinity. These data suggest that IGF-I, in addition to the C-domain, uses surfaces similar to those of insulin in contacting its cognate receptor, although the relative contribution of the side chains of homologous residues varies.

High Serum Levels of IGF-I Contribute to Promotion of Endochondral Ossification in Mandibular Condyle and Cause its Specific Elongation in Acromegaly-like Rats

Mandibular protrusion accompanies acromegaly or acrogigantism. To clarify the detailed mechanisms, we used an acromegaly-like rat model recently developed by exogenous administration of insulin-like growth factor I (IGF-I). Human recombinant IGF-I (640 microg/day) continuously was infused subcutaneously to 10-week-old male rats (n=12) for four weeks. Control, sham-operated animals (n=12) were injected with saline alone. Twelve rats (six from each group) were killed immediately after ending administration at age 14 weeks. Another 12 rats (six from each group) were housed for an additional four weeks after treatment ended. Mandibular condylar length increased significantly in the IGF-I rats compared with the control rats, but no significant intergroup difference was found in the lengths of the coronoid and angular processes. Cartilaginous layer width, bone matrix volume, and the number of osteoblasts in the mandibular condyle increased significantly in the IGF-I group. These histopathological changes in the condyle disappeared after IGF-I administration was discontinued; however, the morphological change in condylar length remained. These findings suggest that mandibular protrusion in patients with acromegaly or acrogigantism may be evoked by superfluous elongation of the mandibular condyle and that such elongation can be induced by endochondral ossification caused by high IGF-I serum levels.

Serum Ghrelin Concentrations are Increased in Children With Growth Hormone Insensitivity and Decrease During Long-Term Insulinlike Growth Factor-I Treatment

BackgroundGhrelin increases food intake, body weight, and growth hormone (GH) secretion. Serum concentrations of ghrelin are low in obese hyperinsulinemic persons, are reduced by infusion of insulin into normal-weight subjects,...

Factor de crecimiento semejante a la insulina tipo I (IGF-I) y cirrosis hepática

Insulin-like growth factor I (IGF-I) is a polypeptide hormone secreted by multiple tissues in response to growth hormone (GH). It is partly responsible for GH activity, and also has glucose-lowering and anabolizing effects. Ninety percent of circulating IGF-I originates in the liver and has autocrine, paracrine, and endocrine effects, the latter on multiple tissues. Liver cirrhosis results in a progressive decline of hepatic IGF-I output, and this factor may become undetectable in advanced disease. Some cirrhosis complications, mainly those nutritional and metabolic in nature (insuline resistance, malnutrition, osteopenia, hypogonadism, intestinal disorders), may be at least partly related to this IGF-I deficiency, since some IGF-I effects represent a reverse image of cirrhosis complications. Despite this, IGF-I replacement therapy has been never suggested for cirrhosis. A number of experimental studies in cirrhotic rats showed that therapy using low-dose recombinant IGF-I exerts two types of effect on experimental cirrhosis: a) liver improvement driven by improved hepatocellular function, portal hypertension, and liver fibrosis; and b) cirrhosis-related extrahepatic disorder improvement driven by improved food efficiency, muscle mass, bone mass, gonadal function and structure, and intestinal function and structure, with a normalization of sugar and amino acid malabsorption, and improved intstinal barrier function, manifested by reduced endotoxemia and bacterial translocation. Subsequently, the first randomized, double-blind, placebo-controlled, pilot clinical trial in a small number of cirrhotic patients showed increased serum albumin and improved energy metabolism as a result of IGF-I use. Further clinical trials are needed to identify adequate IGF-I doses, administration duration and frequency, and the subgroup of cirrhotic patients who will benefit most from this replacement therapy.

Liver transduction with a simian virus 40 vector encoding insulin-like growth factor I reduces hepatic damage and the development of liver cirrhosis

Liver transplantation is the only treatment for advanced liver cirrhosis. Therapies halting the progression of the disease are urgently needed. Administration of recombinant insulin-like growth factor-I (rIGF-I) induces hepatoprotective effects in experimental cirrhosis. Therefore, we analyzed the efficacy of a recombinant simian virus 40 vector (rSV40) encoding IGF-I (rSVIGF-I) to prevent cirrhosis progression. First, transgene expression was evaluated in mice injected with rSV40 encoding luciferase, which showed long-term hepatic expression of the transgene. Interestingly, luciferase expression increased significantly in CCl(4)-damaged livers and upon IGF-I administration, thus liver injury and IGF-I expression from rSVIGF-I should favor transgene expression. rSVIGF-I therapeutic efficacy was studied in rats where liver cirrhosis was induced by CCl(4) inhalation during 36 weeks. At the end of the study, the hepatic levels of IGF-I and IGF-binding protein 3 were higher in rSVIGF-I-treated rats than in control cirrhotic animals. Cirrhotic rats treated with rSVIGF-I had reduced serum bilirubin, transaminases and liver fibrosis scores and increased hepatic expression of hepatocyte growth factor and STAT3alpha as compared to cirrhotic animals. Furthermore, cirrhotic animals showed testis atrophy and altered spermatogenesis, whereas testicular size and histology were normal in cirrhotic rats that received rSVIGF-I. Therefore, rSV40-mediated sustained expression of IGF-I in the liver slowed cirrhosis progression.

Is there a role for recombinant insulin-like growth factor-I in the treatment of idiopathic short stature?

Recombinant human insulin-like growth factor-I (rhIGF-I) has been used during the past decade for the treatment of severe IGF-I deficiency resulting from growth-hormone receptor deficiency (Laron syndrome), and for growth-hormone gene deletion in which inactivating antibodies to exogenous recombinant human growth hormone have developed. In total, about 150 patients have been treated with rhIGF-I for these conditions.1–5 Data for 61 of these patients were used for US Food and Drug Administration approval of rhIGF-I (mecasermin; Increlex, Tercica, Brisbane, CA, USA) and data for another 25 patients in approval of the binary protein complex of rhIGF-I and IGF-I binding protein-3 (mecasermin rinfabate; iPlex, Insmed, Glen Allen, VA, USA), as orphan drugs.

Comparative evaluation of IGF-I gene transfer and IGF-I protein administration for enhancing skeletal muscle regeneration after injury

Developing methodologies to enhance skeletal muscle regeneration and hasten the restoration of muscle function has important implications for minimizing disability after injury and for treating muscle diseases such as Duchenne muscular dystrophy. Although delivery of various growth factors, such as insulin-like growth factor-I (IGF-I), have proved successful in promoting skeletal muscle regeneration after injury, no study has compared the efficacy of different delivery methods directly. We compared the efficacy of systemic delivery of recombinant IGF-I protein via mini-osmotic pump (approximately 1.5 mg/kg/day) with a single electrotransfer-assisted plasmid-based gene transfer, to hasten functional repair of mouse tibialis anterior muscles after myotoxic injury. The relative efficacy of each method was assessed at 7, 21 and 28 days post-injury. Our findings indicate that IGF-I hastened functional recovery, regardless of the route of IGF-I administration. However, gene transfer of IGF-I was superior to systemic protein administration because in the regenerating muscle, this delivery method increased IGF-I levels, activated intracellular signals (Akt phosphorylation), induced a greater magnitude of myofiber hypertrophy and hastened functional recovery at an earlier time point (14 days) after injury than did protein administration (21 days). Thus, the relative efficacy of different modes of delivery is an important consideration when assessing the therapeutic potential of various proteins for treating muscle injuries and skeletal muscle diseases.

Morphological and Histopathological Changes in Tongues of Experimentally Developed Acromegaly-like Rats

An acromegaly-like rat model recently developed by exogenous administration of insulin-like growth factor I (IGF-I) was used to investigate morphological and histopathological tongue changes and clarify whether the changes were reversible. Human recombinant IGF-I (640 microg/day) was continuously subcutaneously infused into ten-week-old male rats for four weeks (IGF-I group; n = 6). Control sham-operated animals were injected saline alone (control group; n = 6). Rats were sacrificed immediately on ending administration at the age of fourteen weeks. Another 12 rats (6 from each group) were housed for an additional four weeks after administration ended. Total IGF-I (human + rat) increased significantly during administration, returning to control levels afterwards. Tongue weights significantly increased with histopathological changes present (increases in the muscle-bundle width, spaces between muscle-bundles and epithelium thickness) in the IGF-I group compared to control rats. Tongue size returned to control levels after discontinuation of IGF-I administration. These findings suggest that the characteristic tongue enlargement was developed experimentally in our acromegaly-like rat model, and that such morphological and histopathological tongue changes are reversible on normalization of circulating IGF-I levels.

The effects of IGF-I on bovine follicle development and IGFBP-2 expression are dose and stage dependent

This study aimed to determine the effect of insulin-like growth factor-I (IGF-I) on early antral bovine follicular development, and the expression of insulin-like growth factor-binding protein-2 (IGFBP-2). Antral follicles separated into three different size groups were cultured for 6 days in medium supplemented with either a low (10 ng/ml) or high (1 microg/ml) dose of human recombinant IGF-I. Oestradiol production by follicles in all size ranges, cultured in the presence of the high concentration of IGF-I, significantly increased by day 6 (P < 0.05). Follicles in the smallest size range, 165-215 microm, cultured in a high dose of IGF-I, were found to be significantly increased in size (P < 0.01). Oocyte health of the largest follicles (281-380 microm) was significantly improved by the addition of IGF-I to the culture medium. mRNA expression of IGFBP-2 was decreased in the granulosa cells of follicles, size range 216-280 microm, cultured with a high dose of IGF-I (P < 0.05). Granulosa cells (P < 0.05) and oocytes (P < 0.01) of the largest follicles (281-380 microm) showed a decrease in IGFBP-2 expression (protein) when cultured in the control and low-IGF-I treatment groups. Therefore, the response of a bovine follicle to IGF-I is both dose and stage dependent. This work supports a role for IGF-I in modulating somatic and germ-cell maturation and development in early antral follicles. Furthermore, the inverse relationship between the level of IGF-I stimulation and IGFBP-2 expression suggests a local regulatory system modulating IGF-I availability.