Functional characterization of insulin-like growth factors in an ancestral fish species, the Shovelnose sturgeon Scaphirhynchus platorhynchus.

Observations from the present study provide the first characterization of the GH-IGF axis in Shovelnose sturgeon Scaphirhynchus platorhynchus, an ancestral fish species. An initial characterization of steady-state IGF-I and IGF-II gene expression in multiple tissues was conducted using real-time RT-qPCR. Overall, the tissues had significantly different profiles of IGF-I gene expression, with the highest IGF-I expression observed in the liver. The highest IGF-II gene expression was also observed in the liver, with minimal or no detection in muscle. A comparison between IGF-I and IGF-II expression within individual tissues revealed higher levels of IGF-II than IGF-I mRNA in the spleen, stomach and trunk kidney, and higher levels of relative IGF-I mRNA expression in the intestine and muscle. The GH-IGF axis was further elucidated by observing the effects of exogenous GH on IGF-I and IGF-II expression in liver and muscle tissue. The results revealed a significant dose-dependent response of both hepatic IGF-I and IGF-II, and muscle IGF-I mRNA expression following rbGH administration. At the highest rbGH concentration (240µg/g BW), IGF-I mRNA levels in liver and muscle peaked significantly at 48h, indicating both hepatic and muscle IGF-I expression to be stimulated by GH. Hepatic IGF-II expression was also stimulated 48h following rbGH administration. Expression of IGF-II mRNA was not inducible in the muscle. Few studies have evaluated the effects of exogenous GH on IGF expression in ancestral vertebrate species, and as such, this research provides valuable insight into the evolution of the somatotropic axis in vertebrates.

Elucidating the roles of gut neuropeptides on channel catfish feed intake, glycemia, and hypothalamic NPY and POMC expression.

Both intrinsic and extrinsic factors modulate food intake and glycemia in vertebrates, in part through interactions with hypothalamic neuropeptide Y (NPY) and proopiomelanocortin (POMC) neurons. The objective of this project was to elucidate the effects of ghrelin (GHRL), gastrin-releasing peptide (GRP), cholecystokinin (CCK), glucagon-like peptide (GLP), pancreatic polypeptide (PP), and peptide YY (PYY) on appetite, glycemia, and hypothalamic expression of NPY and POMC in channel catfish. Catfish were injected intraperitoneally with a single peptide at concentrations of either 0 (control), 50, 100, or 200 ng/g body weight (BW), respectively. Fish were allowed to recover for 30 min, and then fed to satiation over 1 h. Feed intake was determined 1h post-feeding. Catfish injected with GHRL at 50 and 100 ng/g BW and GRP at 200 ng/g BW consumed significantly (P<0.05) less feed compared to controls. A tendency (P<0.1) to suppress feed intake was also observed in the 200 ng/g BW GHRL and PP treatments. PYY, CCK, and GLP had no effects on feed intake. Glycemia was not affected by GHRL, GRP, PP, and PYY treatments, but was suppressed by CCK. A tendency toward lower plasma glucose concentrations was observed in fish administered GLP at 50 ng/g BW. Hypothalamic NPY expression was highly variable and not significantly affected by treatment. POMC expression was also variable, but tended to be reduced by the highest concentration of CCK. These results provide new insight into the roles and regulation of gut neuropeptides in catfish appetite and glycemia.

Exogenous recombinant bovine growth hormone stimulates growth and hepatic IGF expression in shovelnose sturgeon Scaphirhynchus platorhynchus.

Sturgeon are a unique fish for physiological research as they are long-lived, slow-growing, and late-maturing. Furthermore, sturgeon growth hormones appear to share greater structural and molecular similarity with mammalian somatotropins than teleostean somatotropins. In this study, changes in insulin-like growth factor (IGF)-I and IGF-II mRNA expression and corresponding whole-body growth and composition following 6 weeks of bi-weekly recombinant bovine growth hormone (rbGH) administration in shovelnose sturgeon Scaphirhynchus platorhynchus were evaluated. Fish were injected intraperitoneally with 240 µg rbGH/g body weight or a sesame oil sham. Hepatic IGF-I and IGF-II mRNA abundance was significantly higher (P≤0.02) in rbGH-treated fish, as were length (P<0.001) and weight gain (P<0.001). In addition, proximate whole-body analysis demonstrated a significant (P<0.05) increase in protein composition of rbGH-treated fish versus sham-treated fish. There were no significant differences in whole-body moisture, lipid, or ash between the two treatments. These results demonstrate functional roles for GH and IGFs in the promotion of lean growth within this ancient fish species and support the view that the functional effects of GH on hepatic IGF-I expression and somatic growth are conserved from chondostrean to teleostean fishes.