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- Creator:
- Nilmeier, Sara E.
- Description:
- The peptide hormone ghrelin has been shown to stimulate growth hormone (GH) release, appetite, and fat deposition in vertebrates. More recently, ghrelin has been shown to play a role in glucose metabolism in mammals. Ghrelin acts through the growth hormone secretagogue receptor (GHS-R). The GHS-R codes for two gene transcripts, GHS-R1a and GHS-R1b. In tilapia, two forms of ghrelin have been identified, ghrelin-C8 and ghrelin-C10. This study measured the effect of ghrelin on the hormonal regulators involved in glucose metabolism, appetite, and growth (GH/IGF-I axis) in the tilapia, Oreochromis mossambicus. Fish were injected with two doses of ghrelin-C8 and ghrelin-C10. Blood and tissue samples were collected at 2, 4, and 8 h post-injection. The low dose of ghrelin-C8 elevated blood glucose levels at 4 h post-injection. Both ghrelin-C8 and -C10 reduced plasma IGF-I levels and ghrelin-C10 elevated IGF-I mRNA levels in the liver. Ghrelin-C8 and -C10 elevated liver GHR2 mRNA levels, however GHR1 mRNA levels remained unaffected. In the brain, ghrelin-C8 and -C10 treatment elevated both GHS-R1a and GHS-R1b mRNA levels. NPY mRNA levels in the brain, a regulator of appetite, were elevated by ghrelin-C10. These data confirm ghrelin�s role in appetite and glucose metabolism and show that ghrelin up-regulates certain components of the GH/IGF-I axis in tilapia.
- Resource Type:
- Thesis
- Campus Tesim:
- Fresno
- Department:
- Biology
- Creator:
- Upton, Kelli Renee
- Description:
- The general stress response principally results in the release of cortisol, with the overall effect of mobilizing metabolic energy and redirecting it towards homeostatic maintenance. Consequently, an important factor altered by stress is food intake. In several teleost species, a decrease in food intake following stress has been observed, though the neuroendocrine mechanism controlling the reduction in food intake during stress has yet to be determined. These studies were designed to investigate the effect of an acute stress on food intake and brain expression of corticotropin-releasing hormone (CRH), neuropeptide Y (NPY), ghrelin and ghrelin�s receptor and whether these effects are mediated by cortisol. Therefore, metyrapone, a cortisol synthesis inhibitor, was administered via feed in three doses of 10, 25, and 50 mg/kg body weight for 1 wk prior to a 30 min crowding and handling stress. Following the stressor, fish were allowed to feed for 1 h. Stress reduced food intake, while elevating mRNA levels of CRH, an appetite suppressor. Additionally, metyrapone treatment dose-dependently blocked the stress-induced reduction in food intake. While NPY and ghrelin levels were unchanged, an increase in ghrelin receptor activity suggests a function for ghrelin in regulating overall metabolism in response to stress. The elevation of CRH mRNA levels was also reversed with metyrapone treatment, suggesting cortisol and CRH play a role in mediating reduction of food intake during stress in tilapia.
- Resource Type:
- Thesis
- Campus Tesim:
- Fresno
- Department:
- Biology