Sheep Insulin-Like Growth Factors I and II: Sequences, Activities and Assays*

Abstract

This report describes the purification, sequences, and activities of insulin-like growth factors (IGFs) from adult and fetal sheep plasma. IGF-1 from adult sheep is identical to human and bovine IGF-I, except for substitution in the sheep of Ala at residue 66 for Pro in the human and bovine polypeptides. IGF-II from adult sheep differs from bovine IGF-II also by a single amino acid, with residue 62 being Ala in ovine and Thr in bovine IGF-2. The first 10 amino-terminal residues of fetal sheep plasma IGF-I and 92% of the amino acids of fetal IGF-II were identified and found to be the same as those of the corresponding IGFs isolated from adult sheep. Ovine IGF-I was virtually equipotent with human IGF-I in growth-related bioassays and in a RIA for human and bovine IGF-I and inhibited the binding of radiolabeled human IGF-I to type I IGF receptors and to a pure IGF-binding protein. Ovine and bovine IGF-II were also found to be similar to each other in biological and immunochemical activities, and in their binding to type I and II IGF receptors and IGF-binding protein. As observed with human and bovine IGF-I and IGF-II, ovine IGF-I bound slightly better to type I IGF receptors than ovine IGF-II, but bound very poorly to type II IGF receptors. This study shows that IGFs from sheep are very similar to those of human and bovine in structure and activity and defines sensitive radioligand assays specific for ovine IGF-I and ovine IGF-II.

Effect of detoxified karanja (Pongamia spp.) cake on testicular architecture and semen production in ram lambs

“…The IGF-I kit was validated for estimating IGF-I in human serum/ plasma samples. The human IGF-I kit was used for measuring sheep serum/seminal plasma IGF-I levels, since similarity between ovine and human IGF-I in structure and biological activity has been reported (Francis et al, 1989;Breier et al, 1991). The hormonal assays were carried out at the same time in all samples and intra-assay coefficient of variation were 14.8% and 6.3% for testosterone and IGF-I, respectively.…”

Treatment of underfed pigs with GH throughout the second quarter of pregnancy increases fetal growth

“…IGF-I and IGF-II concentrations were determined by RIA of neutralised chromatography fractions devoid of IGFbinding proteins (Carr et al 1995, Francis et al 1989. Insulin was measured by radioimmunoassay (Insulin-CT kit, CIS bio international, Gif-sur-Yvette Cedex, France).…”

Measurement of an analog of insulin-like growth factor-I in blood plasma using a novel enzyme-linked immunosorbent assay

“…This is possible because iodination of IGFs does alter their binding characteristics. For example, iodination of IGF-I has been shown to reduce the affinity of IGF-I for binding to IGF-binding protein-3 from pregnant human serum (Suikkari & Baxter 1991) and radio-iodination of IGF-II abolishes its ability to bind to Type 1 IGF receptors on cultured rat myoblasts (Francis et al 1989). In the LR 3 IGF-I ELISA, the presence of IGF-binding proteins in specimens added to the assay did not reduce the ability of LR 3 IGF-I to form ternary complexes with the assay antibodies.…”

“…These were injected intraperitoneally into pristane (2,6,10,14-tetramethylpentadecane) primed BALB/C mice for production of mouse monoclonal antibodies in ascites fluid. Rabbit anti-IGF immunoglobulins were prepared by immunising New Zealand White rabbits subcutaneously with ovalbumin conjugated either to LR 3 IGF-I or IGF-I (Francis et al 1989). Immunoglobulins were precipitated from Nelson antiserum with saturated ammonium sulphate (Goding 1983).…”