Abstract:
The insulin-like growth factor system (insulin-like growth factor 1, insulin-like growth factor
2, insulin-like growth factor 1 receptor, insulin-like growth factor 2 receptor and six insulinlike
growth factor-binding proteins) and insulin are essential to muscle metabolism and most
aspects of male and female reproduction. Insulin-like growth factor and insulin play important
roles in the regulation of cell growth, differentiation and the maintenance of cell differentiation
in mammals. In order to better understand the local factors that regulate equine physiology,
such as muscle metabolism and reproduction (e.g., germ cell development and fertilisation),
real-time reverse transcription polymerase chain reaction assays for quantification of equine
insulin-like growth factor 1 receptor and insulin receptor messenger ribonucleic acid were
developed. The assays were sensitive: 192 copies/μL and 891 copies/μL for insulin-like growth
factor 1 receptor, messenger ribonucleic acid and insulin receptor respectively (95% limit of
detection), and efficient: 1.01 for the insulin-like growth factor 1 receptor assay and 0.95 for the
insulin receptor assay. The assays had a broad linear range of detection (seven logs for insulinlike
growth factor 1 receptor and six logs for insulin receptor). This allowed for analysis of
very small amounts of messenger ribonucleic acid. Low concentrations of both insulin-like
growth factor 1 receptor and insulin receptor messenger ribonucleic acid were detected in
endometrium, lung and spleen samples, whilst high concentrations were detected in heart,
muscle and kidney samples, this was most likely due to the high level of glucose metabolism
and glucose utilisation by these tissues. The assays developed for insulin-like growth factor 1
receptor and insulin receptor messenger ribonucleic acid expression have been shown to work
on equine tissue and will contribute to the understanding of insulin and insulin-like growth
factor 1 receptor physiology in the horse.
