Session: SAT 109-133-GHRH, GH & IGF Biology & Signaling
Bench to Bedside
Poster Board SAT-130
Methods: 30 native rabbit serum samples of both sexes, 13-weeks old, with different genetic backgrounds (New Zealand White (NZW) and Chinchilla Bastard (CB)) were purchased (Charles-River, Germany). Custom-made, recombinant rabbit IGF-I (rrIGF-I, analytical purity >95%; monomer content >90%) was obtained from PLR (Protein Laboratories Rehovot, Israel). A validation of precision, sensitivity, linearity, and recovery in rabbit serum samples was carried out.
Results: The intra-assay variability of low, medium and high IGF-I rabbit samples (2 samples each) measured in 10 replicates was 2.55, 2.25 and 1.49% respectively. The inter-assay variability from those 6 samples measured in 5 different assay runs was found to be 2.4%. A functional sensitivity of 10ng/ml was confirmed in rabbit samples. Linearity of the assay in native rabbit serum across the range 504-32ng/ml was excellent with a mean observed/expected of 102.9%. Recovery of IGF-I in rabbit samples was assessed by spiking either recombinant human IGF-I (Increlex®, Ipsen) or rrIGF-I. Spiking of rabbit serum with Increlex showed a mean recovery rate of 110.4% (range: 103.7-121.3%). The recovery of rrIGF-I was only 33.9% (range: 29.7-41%), and did not differ when spiking either human or rabbit serum with the rrIGF-I.
Analysis of samples from different rabbit strains showed significantly higher IGF-I concentrations in CB vs. NZW rabbits (p<0.01 in males and p<0.05 in females). In both strains, female rabbits displayed significantly higher IGF-I concentrations (male NZW: 200.6±9ng/ml; female NZW: 285.8±25.9ng/ml; male CB: 265.7±16.3ng/ml; female CB: 361.2±20.8ng/ml).
In summary, our preliminary data indicate that the IDS-iSYS automated IGF-I assay can also be used to measure circulating IGF-I in rabbit serum. The lower recovery for rrIGF is most likely due to a reduced affinity of the antibodies used in the iSYS assay which were raised against human IGF-I. Furthermore, similar to rodents, rabbits also display variations in IGF-I concentrations depending on sex and genetic background.
Disclosure: JM: Employee, Immunodiagnostic Systems. MB: Consultant, Immunodiagnostic Systems. Nothing to Disclose: MB, AH, SM
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