Measurement Of Insulin-like Growth Factor Research Articles

Growth hormone secretion and insulin-like growth factor-1 are related to hyperandrogenism in nonobese patients with polycystic ovary syndrome

Women of normal weight with polycystic ovary syndrome (PCOS) and hyperinsulinemia presented high growth hormone (GH) levels in response to the l-dopa test, suggesting that the action of GH and insulin-like growth factor-1 (IGF-1) might be responsible for the elevation in LH and the consequent hyperandrogenic anovulation observed in normal weight women with PCOS. Insulin resistance and obesity are related to a reduction in GH secretion in obese women with PCOS.

Insulin-Like Growth Factor I Levels in Healthy Children

Measurement of insulin-like growth factor I (IGF-I) levels is used during the assessment of a child for the presence of growth hormone (GH) deficiency and to monitor the efficacy of GH replacement therapy. In either case, robust normative data are required to allow IGF-I values to be expressed as standard deviation scores, enabling comparison between individuals and assessment of change over time. However, IGF-I levels in healthy children are affected by a number of parameters, including age, gender, pubertal status, height, nutrient intake, body composition, intercurrent illness and ethnicity, and the generation of such data requires the collection of samples from significant numbers of healthy children. As external quality assurance schemes for IGF-I and an international standard based on authentic recombinant IGF-I are not widely used, it is imperative for the clinician to understand the performance characteristics and limitations of the IGF-I assay used and to be aware of the source and quality of control data. It must also be recognized that IGF-I measurement is only one component of the diagnostic process and has its limitations, as tissue sensitivity to circulating serum IGF-I levels will differ between individuals.

Type 1 Diabetes Associated with Asymptomatic Acromegaly Successfully Treated with Surgery after Pregnancy: A Case Report

We report a rare case of type 1 diabetes in a woman associated with acromegaly who was treated with surgery after pregnancy. An 18-year-old woman came to our hospital in April, 1998, complaining of thirst, polydipsia, polyuria, appetite loss, body weight loss of 8 kg in a month, and amenorrhea beginning 2 months earlier. Based on laboratory data, she was diagnosed as having type 1 diabetes mellitus. Although we suspected her of having acromegaly because of high growth hormone (GH) levels (6.9 or 8.5 ng/ml), blood levels of insulin-like growth factor 1 (IGF-1) and IGF-binding protein-3 (IGFBP-3) were within normal range and the circadian rhythm of her blood GH levels was normally maintained. Her blood GH level was elevated to 12.6 ng/ml 15 minutes after a TRH administration. Blood GH levels were suppressed from 49 ng/ml to 1.5 ng/ml 4 hours after an oral administration of 2.5 mg of bromocriptine. A magnetic resonance images (MRIs) showed pituitary swelling, but no nodules were found in the pituitary. Therefore, we diagnosed her as having acromegaly and observed her without surgery, while prescribing diet therapy and intensive insulin therapy for diabetes. We started a treatment of oral administration of 7.5 mg of bromocriptine per day for the acromegaly from April 28, 2000, because her elevated GH was suspected of causing her diabetes to be poorly controlled. During a pregnancy from October, 2000 to September, 2001, diabetic control was improved with increased administration of insulin under a constant dose of bromocriptine. She delivered a normal full-term infant. After the bromocriptine therapy was stopped as she hoped to breastfeed, blood levels of GH and IGF-1 became elevated and her diabetic control deteriorated. As her pituitary tumor observed in pituitary MRIs became larger during the course, a transsphenoidal surgery was performed on March 8, 2002. After the surgery, blood levels of GH and IGF-1 lowered and diabetic control improved again. We concluded as follows: to rule out acromegaly in patients with poorly controlled diabetes, 1) measurements of serum GH and IGF-1 should be performed, and 2) pituitary MRIs should be performed if blood levels of GH or IGF-1 are high.

Measurement of insulin-like growth factor axis does not enhance specificity of PSA-based prostate cancer screening

Objectives To examine whether measurement of insulin-like growth factor (IGF)-I, IGF-II, IGF binding protein (IGFBP)-2 or IGFBP-3, alone or in combination, enhanced the specificity of prostate cancer detection among men with a prostate-specific antigen (PSA) level of 3 ng/mL or greater beyond that achieved by the free/total PSA index. Methods Cross-sectional analysis was performed on blood samples taken from 597 asymptomatic men (79% of those biopsied) participating in a community case-finding exercise. All men had a total PSA level of 3 ng/mL or greater and had undergone prostate biopsy. Assays of IGF-I, IGF-II, IGFBP-2, IGFBP-3, and free and total PSA were performed. The predictive performance of a range of measures was assessed using receiver operating characteristic analyses and compared with the free/total PSA index, for all biopsies and for men with a PSA level of 3 to 10 ng/mL. The overall test performance was summarized using the area under the receiver operating characteristic curve (AUC). Results Of the 597 men, 185 (31.0%) had prostate cancer identified at biopsy. When all biopsies were included, the performance of the free/total PSA index (AUC 0.73) was significantly greater than for IGF-I (AUC 0.59; P <0.0001), IGF-I/PSA ratio (AUC 0.65; P = 0.002), IGF-I + IGFBP-3 (AUC 0.59; P <0.0001), IGF-II (AUC 0.66; P = 0.002), and IGF-II + IGFBP-3 (AUC 0.67; P = 0.05). The combined measurement of free/total PSA, IGF-II, and IGFBP-3 resulted in a slight improvement in performance (AUC 0.76; P = 0.01). The results were similar when the analyses were restricted to men with an initial PSA level of 3 to 10 ng/mL. Conclusions We found no evidence that measurement of the IGF axis enhances the specificity of prostate cancer detection in clinical practice beyond that achievable using the free/total PSA index.

Titration of growth hormone dose using insulin-like growth factor-1 measurements: Is it feasible in children?

Titration of growth hormone dose using insulin-like growth factor-1 measurements: Is it feasible in children?

Is insulin-like growth factor-1 monitoring useful in assessing the response to growth hormone of growth hormone-deficient children?

Objective: To assess the relationship between insulin-like growth factor-1 (IGF-1), the growth hormone (GH) dose utilized to treat GH-deficient children and the changes noticed in height-standard deviation score (H-SDS) and height velocity (HV). Study design: We studied 24 prepubertal GH-deficient patients with a mean age of 10.5 ± 1.8 years and a mean bone age (BA) of 8.4 ± 2.1 years. H-SDS for chronologic age (CA) and BA before therapy were −2.6 ± 0.8 and −1.2 ± 0.8, whereas height velocity (HV)-SDS was −1.1 ± 1.5. Serum IGF-1 and insulin-like growth factor binding protein-3 (IGFBP-3) levels were measured before, after 6 and 12 months of GH, and correlated with the GH dose used. Based on the increment of IGF-1 used during treatment, patients were divided into 2 groups: G1 (>1 SDS) and G2 (<1 SDS). HV-SDS and interval height increases were analyzed. Results: HV-SDS, as well as H-SDS for CA and BA during the first year of treatment, were significantly greater than before therapy. IGF-1 SDS increased significantly during the first 6 months of therapy (P <.0003), but increased no further at 12 months despite the use of a higher GH dose (0.1 vs 0.14 IU/kg/day), whereas IGFBP-3 SDS increased at both 6 and 12 months. There was no correlation between the GH dose used and IGF-1 and IGFBP-3 levels. When patients were divided according to their IGF-1 increment during therapy, a significant increase in H-SDS for BA and in HV-SDS was noted only in group 2. Conclusions: The increment in IGF-1 SDS during therapy did not correlate with the interval height increase. IGF-1 measurement may be helpful in monitoring compliance and safety, but seems to be less useful in adjusting the GH dose needed to treat prepubertal GH-deficient children. (J Pediatr 2002;141:606-10)

Insulin-Like Growth Factor I Measurement on Filter Paper Blood Spots

The measurement of insulin-like growth factor I (IGF-I) from extracted whole dried blood spots on filter paper is a simple method allowing sample collection to be carried out by the patient at home. One drop of blood is applied to a filter card, air dried and posted to the laboratory. The IGF-I is dissociated from its binding protein by an acidification and neutralization procedure, and IGF-I is then measured by an enzyme-linked immunosorbent assay. Results from the analysis of IGF-I using blood spots on filter paper compared favourably with those from conventional methods, thus showing it to be an ideal and cost-effective technique for the measurement of IGF-I in both adults and children.

Can measurements of IGF-1 and IGFBP-3 improve the sensitivity of prostate-cancer screening?

Further well designed studies are urgently needed to clarify if use of prostate-specific antigen (PSA) as a diagnostic test for prostate cancer can be improved by incorporating measurements of serum insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding-protein 3 (IGFBP-3), and if these measurements might also identify men at higher risk.

The High Molecular Weight Insulin-Like Growth Factor-Binding Protein Complex: Epitope Mapping, Immunoassay, and Preliminary Clinical Evaluation

Measurements of insulin-like growth factor I(IGF-I), IGF-binding protein-3 (IGFBP-3), and the acid-labile subunit (ALS) are important in assessing the GH-IGF axis. As nearly all IGF-I, IGFBP-3, and ALS circulate in a GH-dependent ternary protein complex, direct determination of the complex may be of significant analytical and clinical importance. We evaluated a panel of monoclonal antibodies (mAb) to human IGFBP-3 and classified them into four groups (G-1 to G-4). G-1 antibodies recognized epitopes that mapped at or near IGFBP-3 ligand (IGF)-binding site. This region overlapped with the G-2 defined region, which, in turn, overlapped with G-3 epitopes defined by one antibody (mAb 3). Only G-1 and G-3 antibodies paired without interference. mAb 9 recognized a conformational epitope (G-4), and mAb 10 was nonreactive. In pairwise mixed antibody evaluation, mAbs in G-2 and G-3 showed simultaneous binding to serum IGFBP-3 complexes in combination with an anti-IGF-I or an anti-ALS antibody. On this basis, two novel enzyme-linked immunosorbent assays (ELISAs) involving IGFBP-3/IGF-I (ELISA-1) and IGFBP-3/ALS (ELISA-2) recognition partners were developed, both demonstrating acceptable analytical performance characteristics. IGFBP-3 complexes measured by ELISA-1 and -2 in samples from normal individuals and subjects with GH deficiency, acromegaly, and GH receptor deficiency more tightly correlated with IGF-I, IGFBP-3, and ALS than IGF-II. ELISA-1 determinations were comparatively more age dependent and, in comparison to ELISA-2, showed better discriminations among the various sample groups, particularly among GH receptor deficiency, normal, and GH deficiency subjects. The development of IGFBP-3 complex ELISAs may simplify diagnostic applications and facilitate investigations of the physiological relevance of the ternary complex formation.

Monthly measurements of insulin-like growth factor I (IGF-I) and IGF-binding protein-3 in healthy prepubertal children: characterization and relationship with growth: the 1-year growth study.

The usefulness of measurements of IGF-I or IGF-binding protein-3 (IGFBP-3) in the clinical management of growth disorders is dependent on the extent of physiologic variation in their concentrations. Our purpose was therefore to investigate the longitudinal intraindividual variation in serum concentration of IGF-I and IGFBP-3 in healthy prepubertal children. Monthly serum samples and auxologic measurements were taken over a period of 1 y from 65 prepubertal children (38 boys, 27 girls; mean age 9.1 y, range 7.8-10.8). Concentrations of IGF-I and IGFBP-3 were measured by RIA. The mean (+/-SD) serum concentration of IGF-I in the children was 165 +/- 42.0 microg/L, with a mean coefficient of variation (CV) of 13.9% around the annual mean serum concentration for each child. The corresponding mean concentration of IGFBP-3 was 3273 +/- 604.5 microg/L, and the mean CV for each child was 9.7%. These monthly longitudinal variations in IGF-I and IGFBP-3 were parallel to changes in longitudinal growth. Short-term changes (1 mo) in IGF-I were positively correlated with changes in weight (r(s) = 0.42, p < 0.0005) and body mass index (r(s) = 0.45, p < 0.0005), and negatively correlated with minor intercurrent illnesses (-0.32; p < 0.05). Seasonal fluctuations also occurred, with short term changes in IGF-I (1 mo) and IGFBP-3 (3 mo), increasing with increasing outdoor temperatures (r(s) = 0.30, p < 0.05 and r(s) = 0.39, p < 0.005, respectively). We conclude, that there are significant changes in both IGF-I and IGFBP-3 that occur in association with growth, and that IGF-I is more sensitive than IGFBP-3 to short-term changes in weight, body mass index, and intercurrent illnesses. Physiologic short-term changes must therefore be taken into consideration when using serum levels of IGF-I or IGFBP-3 in the evaluation of the short or slowly growing child.

Increased milk levels of insulin-like growth factor 1 (IGF-1) for the identification of bovine somatotropin (bST) treated cows.

The present EU moratorium banning the use of bST to increase milk yield implies the need for official controls. Our study aimed to identify milk from bST treated cows via the induced increase of insulin-like growth factor 1 (IGF-1) concentrations. A non-extraction radioimmunoassay for IGF-1 was improved and thoroughly validated for milk. Accuracy was 99% recovery in a fortified sample material, the precision was 5.1% intra-assay variation and 13.4% inter-assay variation. Parallelism was proved by a dilution experiment which yielded a regression line with a slope (-0.7%) not significantly different from zero (P = 0.534). Naturally occurring milk IGF-1 levels were recorded in 5777 random milk samples from the Bavarian dairy cow population. In samples from lactation week 7 to 33, the effect of somatic cell count (SCC), protein content and parity could be quantified and corrected; thus a normal distribution (-0.068 mean +/- 0.440 s) of the corrected logarithmic IGF-1 levels (corr ln IGF-1) was obtained. IGF-1 concentrations occurring in milk from bST treated cows were recorded in 33 Brown Swiss cows treated once with rbST (POSILAC). Mean corr in IGF-1 levels increased by 0.828 and 0.477 in first parity and older cows, respectively. Thus 60% and 29%, respectively, of the positives could be detected at a 95% probability. If our results are confirmed in experiments with more bST treated cows and with prolonged treatment intervals. IGF-1 measurements might be useful to monitor for bST application in milk samples.

Immunoassay of insulin-like growth factor binding protein-1

Accurate measurement of insulin-like growth factor (IGF) binding protein-1 (IGFBP-1) is important for precise definition of its physiological roles and potential diagnostic values. Because altered phosphorylation results in altered IGFBP-1 immunoreactivity, current assays may significantly underestimate or fail to detect physiological changes in the IGFBP-1 concentrations. We developed three ELISAs (ELISA 1-3) using a common capture but three different detection antibodies. IGFBP-1 in serum, synovial fluid (SF), cerebrospinal fluid (CSF), and amniotic fluid (AF) were measured before and after treatment with alkaline phosphatase (ALP). Among the methods, only ELISA-1 was unaffected by IGFBP-1 phosphorylation and generated identical results before and after ALP treatment. The serum and SF values by ELISA-2 and -3 were lower by approximately 4- to 10-fold, but increased after ALP treatment to within 66-98% of those by ELISA-1. The medians in AF, and to a lesser extent in CSF, by all methods were similar and did not change significantly after dephosphorylation. ELISA-1 showed excellent correlation with ELISA-2, ELISA-3, and a commercial IGFBP-1 IRMA only after ALP-treated samples were analyzed by the comparative methods. ELISA-1 is highly specific for IGFBP-1 and demonstrated acceptable analytical performance characteristics.

Sequential Changes in Insulin‐Like Growth Factor 1, Plasma Proteins, and Total Body Protein in Severe Sepsis and Multiple Injury

Our group wanted to test the hypothesis that plasma levels of insulin-like growth factor 1 (IGF-1), transferrin, and prealbumin are useful markers of nutritional progress in severe sepsis and multiple injury. Measurements of IGF-1 and plasma proteins were made in critically ill patients as soon as they were hemodynamically stable and 5, 10, 15, and 21 days later. The magnitude and direction of the measured changes were compared with the magnitude and direction of the change in total body protein in the same time period. Fourteen patients with severe sepsis and 10 multiply injured patients were studied. As a group they had an increased metabolic expenditure that peaked at 153% of normal and lost approximately 12.0% of total body protein. An early fall in IGF-1 and plasma proteins accompanied a marked acute phase response, and recovery occurred while hypermetabolism and net proteolysis continued. No correlation existed between changes in IGF-1 or plasma proteins and the change in total body protein. Plasma levels of IGF-1, transferrin, and prealbumin are not useful for following changes in protein stores early in the course of critical illness.

Measurement of insulin-like growth factor (IGF)-II binding to purified IGF binding proteins 1–6: comparison of charcoal adsorption and high performance size exclusion chromatography

Insulin-like growth factor (IGF) binding to IGF binding proteins is commonly assessed by adsorbing free IGF to albumin-coated charcoal and quantitating bound IGF in the supernatant, but the validity of this technique has been questioned and many variations have been described. We compared the measurement of binding affinity and capacity of purified IGFBPs 1–6 for IGF-II using charcoal adsorption and Superdex G75 high performance size exclusion chromatography (HPSEC) to separate free and bound 125I-IGF-II. Optimal HPSEC recovery and resolution was obtained for IGFBP-1 and IGFBP-6 with low salt buffer (0.1 M sodium phosphate, pH 7.4), whereas phosphate buffer supplemented with 0.5 M NaCl was optimal for IGFBPs 2–5. Measurement of binding of 125I-IGF-II to IGFBPs 3–5 using the charcoal assay was also increased by the use of high salt buffer. Under optimal conditions, charcoal measurements of 125I-IGF-II binding to IGFBPs 1–5 were consistently lower than HPSEC measurements. By competitive binding using unlabeled IGF-II, the binding affinity of each of the IGFBPs for IGF-II was the same using both methods. Similarly, binding affinities as measured by charcoal assay were not affected by buffer composition. Differences in total binding obtained using the two methods and under different conditions were therefore due to differences in binding capacity. Charcoal adsorbs 15% of cross-linked 125I-IGF-II:IGFBP complexes which may partially explain the lower binding capacity for IGFBPs 1–5 determined by charcoal adsorption. Charcoal adsorption and HPSEC, therefore, are both valid methods for the measurement of binding affinities of IGFBPs for IGF-II, but assay conditions must be validated prior to measurement: of binding capacity.

Serum insulin-like growth factor 1 in congenital heart disease.

Serum insulin-like growth factor 1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), and a range of growth and nutritional variables were investigated in 62 infants with congenital heart disease and healthy controls. Infants with congenital heart disease were small, underweight, and had a reduced energy intake. Serum IGF-1 and IGFBP-3 concentrations were significantly reduced. Decreased IGF-1 and IGFBP-3 levels are observed in nutritional deficiency; similar findings in congenital heart disease suggest that undernutrition contributes to the poor growth of these infants. Serial measurements of serum IGF-1 and IGFBP-3 may be helpful in monitoring the effect of nutritional treatment in congenital heart disease.

Measurement of human IGF-II using Sephacryl extraction: a rapid and reliable assay method.

Measurement of insulin-like growth factor II (IGF-II) in human serum is complicated by the presence of IGF binding proteins and usually involves cumbersome extraction procedures followed by radioimmunoassay. We have utilized an extraction process developed for measuring insulin-like growth factor II in ovine serum using Sephacryl HR100, and have applied this to the extraction of human samples followed by radioimmunoassay for human IGF-II. The assay yielded 98% recovery of unlabelled IGF-II, parallelism between dilutions of eluate and the standard curve, complete removal of binding proteins and near-complete removal of IGF-I, and intra- and interassay coefficients of variation of 5% and 9%, respectively. The normal range for serum IGF-II in women was 490-1056 micrograms/L, and IGF-II levels were positively correlated with serum concentrations of insulin-like growth factor binding protein-3 (IGFBP-3) but not with IGF-I levels. Mean serum concentrations of IGF-II were reduced below normal in a number of hypopituitary patients and children with short stature and IGF-II concentrations in these subjects correlated positively with IGF-I and IGFBP-3. In acromegalic patients IGF-II levels were usually normal and were negatively correlated with IGF-I concentrations. From our experience with the above results the present assay appears particularly suitable for clinical measurements and research projects where high sample throughput is required.

An age-related decrease in the concentration of insulin-like growth factor binding protein-5 in human cortical bone

The skeletal contents of insulin-like growth factor-2 (IGF-II), insulin-like growth factor binding protein-5 (IGFBP-5), and insulin-like growth factor binding protein-3 (IGFBP-3) were determined in duplicate samples of human femoral cortical bone obtained from 64 subjects (44 males and 20 females) between the ages of 20 and 64 years. The results of these quantitative measurements revealed an age-related decrease in the femoral cortical content of IGFBP-5 (r = -0.272, P = 0.031) in the total population. Although the femoral cortical content of IGF-II did not show a similar decrease with age, it could be correlated to the femoral cortical content of IGFBP-5 (r = 0.442, P < 0.001). In contrast, the femoral cortical content of IGFBP-3 did not decrease with age and could not be correlated to the femoral cortical contents of either IGFBP-5 or IGF-II. Comparisons of these results with previous measurements of insulin-like growth factor-1 (IGF-I) and transforming growth factor-beta (TGF-beta), in extracts of the same bones, showed significant cross-correlations between the femoral cortical contents of each of these growth factors and the femoral cortical contents of IGFBP-5 (r = 0.625 for IGF-I versus IGFBP-5, r = 0.554 for TGF-beta versus IGFBP-5, P < 0.001 for each) but not IGFBP-3.(ABSTRACT TRUNCATED AT 250 WORDS)

The impact of obesity, fat distribution, and energy restriction on insulin-like growth factor-1 (IGF-1), IGF-binding protein-3, insulin, and growth hormone

The aim of this study was to characterize the association between serum insulin-like growth factor-1 (IGF-1) and obesity, as well as fat distribution, before and during moderate energy restriction (1,200 kcal/d). In 51 females and nine males having a body mass index (BMI) between 27 and 39 kg/m 2, relationships between serum IGF-1, IGF-binding protein-3 (IGFBP-3), insulin, growth hormone (GH), blood glucose, and anthropometric measurements of body fat were examined. The patients were studied before treatment and again after 8 and 16 weeks of dieting. Visceral adipose tissue (AT) was estimated by anthropometric computed tomography (CT)-calibrated equations. In females, IGF-1 was inversely associated with the abdominal sagittal diameter (SagD) and with the visceral AT ( r = −.41, P = .006). No significant correlations were found between IGF-1 and BMI or other indices of adiposity. Weight loss caused a temporary increase in IGF-1 concentrations ( P = .03) and continued decrements in blood glucose levels ( P = .0004 at 16 weeks). A statistically significant inverse correlation between IGF-1 and blood glucose levels was present before ( r = −.30, P = .02) and after 8 ( r = −.37, P = .007) and 16 ( r = .02, P = .02) weeks of dietary treatment. Both serum IGF-1 and insulin levels were positively correlated with serum IGFBP-3 levels ( r = .34, P = .009 and r = .34, P = .008, respectively). We conclude that IGF-1 levels in obese females reflect the intraabdominal fat mass rather than obesity per se. IGF-1 and blood glucose levels are inversely correlated in obesity before and during energy restriction.

A novel method for the extraction of sheep insulin-like growth factors-I and -II from plasma prior to radioimmunoassay.

The measurement of insulin-like growth factors (IGFs) in plasma is complicated by the presence of high-affinity IGF-binding proteins (IGFBPs). Consequently, the IGFBPs need to be removed or their IGF-binding effects need to be neutralized prior to assaying samples for IGFs. It was observed that IGFs but not IGFBPs from sheep plasma bind to the size-exclusion gel Sephacryl S-100 HR at a low pH and that the IGFs can subsequently be eluted off at a neutral pH. From this observation a convenient method was developed for the extraction from plasma of ovine (o) IGF-I and -II free from detectable IGFBPs with close to 100% recovery. When assayed in homologous sheep IGF-I and -II radioimmunoassays the Sephacryl-extracted plasma samples gave dose-response curves which were parallel to purified oIGFs. Furthermore, the results obtained by Sephacryl extraction were highly correlated with those found by the established Sephadex G-75 extraction procedure.

Validation of a Heterologous Radioimmunoassay for Insulin-Like Growth Factor-1 in Chicken Serum.

Chicken serum insulin-like growth factor-1 (IGF-1) was extracted with an acid ethanol solution and submitted to a heterologous radioimmunoassay (RIA) after lyophilization. In the RIA, recombinant human IGF-1 (rhIGF-1) was used for standards and radioactive ligand. Anti-rhIGF-1 antiserum used was provided by the NIDDK. The inhibition curves for extracts of two-fold serial dilutions of chicken sera were essentially parallel to those for the standard and human sera. The recovery of rhIGF-1 added to chicken sera was 100.1±0.7% (n=30). The intrrassay and interassay variability (CV) for the RIA was 6.9% (n=10) and 7.6% (n=3), respectively. The limit of sensitivity for measurement of IGF-1 extracted from chicken serum was 5 pg/assay tube. Hypophysectomy significantly reduced serum levels of IGF-1 by 80% as compared to sham-operated control chicken. Dwarfing gene (dw) also significantly reduced serum IGF-1 by 89% compared to normal control. These results indicate that the present heterologous RIA was validated for measurement of immunoreactive IGF-1 levels in chicken serum.