Serum insulin-like growth factor 1 in the aging horse.

BACKGROUND: Insulin-like growth factor 1 (IGF-1) has important roles in anabolic processes in the musculoskeletal system and has been reported to decrease with age in both people and horses. OBJECTIVES: The objective of this study was to determine serum IGF-1 levels in the aging horse from early to late adulthood (age range 5-27 years). METHODS: Healthy horses (n = 72) were used in a cross-sectional study, while 37 paired serum samples were available for a longitudinal study. Serum IGF-1 protein was determined using an ELISA kit validated for use in equine samples. RESULTS: No association was found between serum IGF-1 levels and age in the cross-sectional study. In the longitudinal study, a latent variable model fitted to the data revealed that horses in general experienced a 5.2% increase of serum IGF-1 levels over a 5-year period, but horses crossing a change point around 9 years of age between the 2 samples experienced an 11.0% decrease. CONCLUSIONS: In this study, there was no evidence for aging being a factor in changes of IGF-1 levels in an adult and old horse population.

Validation of the IDS Octeia ELISA for the determination of insulin-like growth factor 1 in equine serum and tendon tissue extracts.

BACKGROUND: Insulin-like growth factor (IGF-1) is an important mediator of tissue repair in horses. OBJECTIVES: The aim of the study was to evaluate whether IGF-1 could be measured reliably in equine serum and tendon tissue extracts, using an IGF-1 ELISA kit developed for human serum and plasma. METHODS: A glycyl-glycine pretreatment protocol of samples was compared with the pretreatment procedure recommended by the manufacturer. Intra- and inter-assay imprecision were evaluated by repeated measurements of equine serum pools. Assay inaccuracy was determined based on the linearity of serially diluted equine serum samples and tendon tissue extracts. The recovery of IGF-1 was evaluated in serum and tendon tissue extracts spiked with known amounts of IGF-1. RESULTS: The range of IGF-1 released using the manufacturer's pretreatment was between 23% and 56% of the amount released using the gly-gly pretreatment in different equine samples. In serum pools with low, intermediate, and high IGF-1 concentrations, intra-assay imprecision was 4.0%, 4.0%, and 3.1%, respectively, and inter-assay imprecision was 13.9%, 7.3%, and 12.8%, respectively. The recovery of serially diluted serum was 96 ± 3% when diluted with serum, and 72 ± 15% when diluted with PBS. The recovery after dilution was 108 ± 17% in tendon tissue extracts. Recovery from serum spiked with a fixed amount of IGF-1 was 101 ± 5% and 99 ± 7% from tendon tissue samples. CONCLUSIONS: The IDS Octeia IGF-1 ELISA kit can be used for measuring IGF-1 in equine serum and tendon tissue extract after pretreatment with glycyl-glycine.