Meeting Abstract
69.2 Thursday, Jan. 6 Peripheral ghrelin stimulates feeding and positive energy balance in a sciurid hibernator HEALY, JE*; BATEMAN, JL; GEARHART, CN; OSTROM, CE; FLORANT, GL; Colorado State University jehealy@rams.colostate.edu
Mammals that hibernate undergo a robust circannual cycle of body mass gain and loss mediated by food intake. Hibernators are aphagic in winter, normophagic in spring and summer, and hyperphagic in autumn. The pathways involved in control of food intake in these animals have not been fully elucidated. Ghrelin is an orexigenic hormone known to increase feeding in all mammals studied so far, but has not until recently been studied in hibernators. In other mammals, it stimulates feeding through phosphorylation and activation of AMP-activated protein kinase (AMPK), which in turn phosphorylates and deactivates acetyl Co-A carboxylase (ACC), a committed step in fatty acid synthesis. In order to determine the effects of exogenous ghrelin on food intake and metabolic factors, such as non-esterified fatty acids (NEFAs), and hypothalamic AMPK and ACC in hibernators, we peripherally injected ghrelin into golden-mantled ground squirrels in all four seasons. We recorded changes in food intake and body mass over a 6 hour period post injections. During the winter season, we euthanized squirrels 2 hours post injection, and removed brains and blood for later analysis. We performed Western blots to determine changes in hypothalamic AMPK and ACC, and a colorimetric assay to determine changes in plasma NEFAs. We found that food intake and body mass significantly increased with ghrelin injections versus saline controls, even in animals injected during the aphagic winter season. Injected ghrelin caused an increase in phosphorylation of AMPK in summer and winter animals and ACC in summer animals, but didn’t have an effect on ACC in winter animals. Ghrelin-injected animals also had increased levels of plasma NEFAs over saline controls. This study is the first to show an effect of injected ghrelin on a hibernator.
