Measurement of Somatomedin-Related Peptides in Fetal, Neonatal, and Maternal Rat Serum by Insulin-Like Growth Factor (IGF) I Radioimmunoassay, IGF-II Radioreceptor Assay (RRA), and Multiplication- Stimulating Activity RRA after Acid-Ethanol Extraction*

Abstract

Previous measurements of somatomedins (Sms) and insulin-like growth factors (IGFs) in maternal and fetal serum have yielded contradictory results. We have, therefore, measured maternal, fetal, and neonatal rat serum with two highly specific assays: 1) IGF-I/Sm-C RiA and 2) a highly specific IGF-II/rat placental membrane radioreceptor assay (RRA). In addition, we have made measurements with a less specific multiplication-stimulating activity (MSA)-rat placental membrane RRA. To avoid possible serious artifacts created by Sm-binding proteins, preliminary acid-ethanol extraction of serum was performed. Results are expressed in terms of a reference human serum with an assigned potency of 1 U/ml. Maternal RIA IGF-I fluctuated between 1.1-1.4 U/ml from the 17th day of pregnancy to the 25th day after delivery (nonpregnant rat serum pool, 1.25 +/- 0.22 U/ml). On day 21 of gestation, fetal serum radioimmunoassayable IGF-I was 1.03 +/- 0.03 U/ml. After birth, radioimmunoassayable IGF-I fell and reached .19 +/- 0.03 U/ml at 18 days of age, but rose to 0.71 +/- 0.04 U/ml at 25 days of age. At term, maternal radioreceptor assayable IGF-II was 2.18 +/- 0.27 U/ml (nonpregnant female pool, 1.4 +/- 0.12). By the 25th postpartum day, radioreceptor assayable IGF-II was 1.39 +/- 0.12 U/ml. Radioreceptor assayable IGF-II in fetal serum on day 19 was 3.26 +/- 0.48 U/ml and rose to 5.37 +/- 0.66 U/ml on the day of delivery. A further rise to 8.92 +/- 1.03 occurred on day 5. A subsequent fall to 2.41 +/- 0.05 U/ml was observed on day 25. The patterns of results of the MSA RRA in fetal and neonatal rat serum were similar to that obtained with the IGF-II RRA. We now conclude that radioimmunoassayable IGF-I is present in higher concentrations than previously reported in term fetal rat serum and that radioreceptor assayable IGF-II is selectively elevated in rat fetal and neonatal life and may have unique metabolic and growth-promoting significance.U

Parathyroid hormone increases the concentration of insulin-like growth factor-I and transforming growth factor beta 1 in rat bone.

“…The matrix concentrations of IGF-ll in the vehicle-treated animals did not significantly change with time either. There was a remarkable 60% decline in circulating IGF-II during the course of the experiment (P = 0.0001, ANOVA), indicating that the decline in serum IGF-II that can be observed in rats within a few days after birth (21,22), continues into early adulthood (Fig. 4 B).…”

Increased weight gain, nitrogen retention and muscle protein synthesis following treatment of diabetic rats with insulin-like growth factor (IGF)-I and des(1–3)IGF-I

“…Urinary 3-methylhistidine was measured by an automated method [11] after initial hydrolysis and ionexchange-chromatography steps [12]. Muscle RNA contents were measured as described by Munro IGF-I was measured in acid/ethanol extracts of plasma by a modification [15] of the original procedure [16]. With the antiserum used, des(I-3)IGF-I and rat IGF-I cross-reacted to about 50 % the extent of human IGF-I.…”

Insulin-like Growth Factors in a clinical setting: Review of IGF-I

“…Thus, there is still a need for rapid, technically simple and accurate assay to determine IGF-I bioactivity 27 . The main problem is standardization of methods regarding the issue of interference with IGF-I binding proteins, causing inaccurate and therefore unreliable results 28 . The binding proteins can be removed by acid gel filtration chromatography 29 .…”

“…Hence, commercial laboratories do not use it, preferring acid displacement of binding proteins and then precipitated with ethanol in the investigated material. For a valid assay, only IGF-I should remain in the sample 28 . The incomplete removal of small molecules of binding proteins primarily not bound to ALS causes measurement errors.…”