Date of Award
Master of Science
Evaluating the growth axis of an ancient species such as the Shovelnose Sturgeon Scaphirhynchus platorynchus can aid in understanding the divergence of growth factors among a vast evolutionary span of vertebrates. It is hypothesized, that similar to teleosts and tetrapods, growth hormone (GH) mediates and stimulates the anabolic actions of insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II) in sturgeon. Using Shovelnose Sturgeon as a model, the objectives of this research were to identify the acute and chronic effects of exogenous recombinant bovine GH (rbGH) on IGF-I and IGF-II gene expression and investigate the roles IGF's have on whole animal growth and nutrient partitioning in the presence of chronic rbGH administration. In the first experiment, fish were injected with five different concentrations of rbGH (0, 30, 60, 120, 240 μg/g body weight (BW) rbGH)) and sampled at five time points (6, 12, 24, 36, 48-h post-injection). Hepatic and muscle tissue specimens were rapidly excised following euthanasia for mRNA isolation and quantitative real-time polymerase chain reaction (qRT-PCR) analysis of IGF expression. qRT-PCR analysis indicated hepatic IGF-I and IGF-II expression was significantly higher than muscle IGF-I expression, and IGF-II was not expressed in muscle. The highest rbGH concentration (240 μg/g BW) significantly increased hepatic IGF-I and IGF-II mRNA and muscle IGF-I mRNA expression levels at 48 hours post injection. After 6 weeks of bi-weekly rbGH administration in a second experiment, fish injected with rbGH at 240 μg/g BW gained significantly more length and weight than fish injected with the sham (0 μg rbGH; sesame oil), and whole body proximate analysis revealed rbGH treated fish had significantly higher amounts of protein. This research aids in understanding the regulatory and evolutionary principles of the vertebrate somatotropic axis through characterizing the endocrine regulation of growth in Scaphirhynchus sturgeon.
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