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Validation of Heterologous Radioimmunoassays (RIA) for Growth Hormone (GH) and Insulin-Like Growth Factor (IGF)-I in Phocid, Otariid, and Cetacean Species
Abstract: Growth hormone (GH) is a homeorhetic hormone that coordinates diverse physiological processes to partition nutrients toward lean tissue accretion and milk production, and to inhibit utilization of nutrients by adipose tissue, especially during periods of energy deficiency. Due to age-related declines in GH, GH is negatively correlated with overall growth rate and lipid accretion but positively associated with protein accretion. Circulating GH influences peripheral tissues directly or indirectly and is primarily mediated via an insulin-like growth factor (IGF)-I. Similar to GH, age and nutrition influence IGF-I secretion. In general, IGF-I is positively associated with growth rate and accretion of protein. Since purified pinniped or cetacean GH and IGF-I are not available, heterologous assay techniques must be employed to quantify concentrations of these hormones. Critical to the reliability of heterologous assays are the proper execution of validations to demonstrate the accuracy and precision of the assay for each new species of interest. In this study, we developed and validated heterologous radioimmunoassays for seven marine mammal species using porcine and human antisera for GH and IGF-I quantification, respectively. Sensitivity, recovery of mass, assay precision, parallelism, and dilution linearity were determined for each assay and species. Both assays exhibited excellent parallelism and linearity. Appropriate concentrations of hormone were quantified throughout the range of the standard curve. Importantly, using these assays, we have demonstrated that serum concentrations of GH and IGF-I change with age and nutrient intake in these species. Validation of these assays allows evaluation of metabolic hormones that may provide unique perspectives on physiological regulation of differential growth and nutrient allocation for diverse marine mammal species.
Key Words: assay validation, growth hormone, insulin-like growth factor-I, phocid, otariid, cetacean, multi-species, radioimmunoassay
Document Type: Research article
Page Numbers: 19-31