Validation of a heterologous radioimmunoassay for insulin-like growth factor-I in bovine serum

Abstract

A quantitative, repeatable, heterologous radioimmunoassay (RIA) for insulin-like growth factor-I (IGF-I) was developed for bovine serum. Untreated serum could not be assayed due to interference by IGF-I-binding protein. Serum acidified to pH 3.6 in glycine-HCl (0.1 mol/l) for 24 h at 37 degrees C and neutralized with NaOH produced inhibition curves non-parallel to the [Thr59]-IGF-I standard. Neutralization by 40-fold dilution of acidified serum samples with assay buffer produced inhibition curves nearly parallel to the IGF-I standard. Complete parallelism was achieved by utilizing preprecipitated normal rabbit serum-sheep anti-rabbit gamma-globulin to separate antibody-bound 125I-labelled IGF-I from free 125I-labelled IGF-I. Recovery of IGF-I (1.3-52.3 fmol) added to serum was quantitative. The sensitivity of the RIA (n = 6) was 8.25 +/- 0.17 (S.E.M.) fmol. Intra- and interassay coefficients of variation were 3.03 and 4.95% respectively. Serum IGF-I levels measured in beef calves at weaning were positively correlated with weaning weight, total weight gain from birth to weaning and average daily weight gain. In conclusion, a heterologous RIA for IGF-I in beef serum which is sensitive, accurate, precise and repeatable has been developed.

Profiles of serum IGF-I concentrations in calves from birth to eighteen months of age and in cows throughout the lactation Cycle

“…The reasons for the species differences in this sexuaf dimorphism are unknown. In the present study, a portion -0.22 -0.54 DISCUSSION The age-dependent increases in serum IGF-I levels found in the calftrial are in accordance with previous findings in mice (Blair et al 1987), rats (Handelsman et al 1987), pigs (Scanes et al 1987), calves (Lund-Larsen et al 1977;Holland et al 1988;Abribat et al 1990), chickens (Goddard et al 1988) and humans (Furlanetto et al 1977;Silbergeld et al 1986). With the exception of the report by Lund-Larsen etal.…”

Effect of feed restriction on serum somatotropin, insulin-like growth factor-I-(IGF-I) and IGF binding proteins in cyclic heifers actively immunized against growth hormone releasing factor

“…Serum IGF-I was assayed using glycylglycine hydrochloride extraction procedures as described (24) with modifications (25,26). The standard source was recombinant human IGF-I (Amgen, Thousand Oaks, CA).…”

Effect of Somatotropin and/or Equine Chorionic Gonadotropin on Serum and Follicular Insulin-Like Growth Factor I and Insulin-Like Growth Factor Binding Proteins in Cattle1

“…Intraassay CV and sensitivity, as described previously, were 9.6% and 0.6 ng/ml, respectively. Serum and FFL concentrations of IGF-I were determined as described by Houseknecht et al [31] with modifications [32,33]. Addition of 0.5, 1, and 4 ng of IGF-I (before extraction) to FFL yielded recoveries of 79, 81, and 83%.…”