Endocrine Regulation of Growth in An Ancient Fish Species, the Shovelnose Sturgeon

Evaluating the growth axis of an ancient species such as the Shovelnose Sturgeon Scaphirhynchus platorhynchus 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. The objective of this research was to identify the acute effects of exogenous GH on IGF-I and IGF-II gene expression in Shovelnose Sturgeon. Fish were injected with five different concentrations of GH and sampled at five time points for hepatic and muscle mRNA isolation and real-time PCR analysis of IGF expression. Hepatic IGF-I and IGF-II expression was higher (~50x) than muscle IGF-I expression, and IGF-II was not expressed in muscle. The highest GH concentrations (240 and 120 μg/g BW) significantly increased IGF-I expression in the liver and remained elevated at 48 hours. IGF-I expression in the muscle was significantly increased 36 hours after administration of 240 μg GH. This research aids in understanding the regulatory and evolutionary principles of the vertebrate somatotropic axis and provides the first look into the endocrine regulation of growth in Scaphirhynchus sturgeon.