Meeting Abstract

P2.36  Friday, Jan. 4  Effect of Glucose on Ghrelin and on the GH/IGF-I Axis in the Tilapia, Oreochromis mossambicus DOROUGH, C.P.*; HIRANO, T.; GRAU, E.G.; RILEY, L.G.; California State University-Fresno; Hawaii Institute of Marine Biology, University of Hawaii; Hawaii Institute of Marine Biology, University of Hawaii; California State University-Fresno cdorough2k@msn.com

Ghrelin (GRLN), a novel stomach peptide, is the endogenous ligand for ghrelin receptor (GRLN-R). We have shown that GRLN has a stimulatory effect on growth hormone (GH) release from the pituitary in addition to stimulating feeding in the tilapia, Oreochromis mossambicus. Reports in mammals have shown that GLRN plays a role in glucose metabolism and conversely, glucose regulates plasma GRLN levels. We have preliminary evidence that GRLN stimulates the release of glucose from cultured hepatocytes. The current study was conducted to investigate the effect of intraperitoneal injection of glucose (2 mg/g body weight) on GRLN plasma levels and on the growth hormone/insulin-like growth factor-I (IGF-I) axis in the tilapia. Six h post-injection, plasma was collected for the measurement of GRLN, GH, and IGF-I levels as well as liver for mRNA expression levels of GH-R and IGF-I, stomach for ghrelin mRNA expression, and pituitary for GRLN-R mRNA expression. Glucose treatment significantly increased plasma GRLN levels but did not alter stomach GRLN mRNA levels. GRLN-R mRNA levels in the pituitary were significantly elevated while GHS-R1b was not. Despite an increase in the levels of GRLN in the plasma and GRLN-R in the pituitary, plasma GH levels were not altered after glucose treatment. However, glucose significantly reduced plasma IGF-I levels, but did not alter liver mRNA levels of GH-R and IGF-I. These data suggest that an elevation in blood glucose, which occurs naturally during fasting, is one of the metabolic signals that lower blood IGF-I levels and inhibits growth while at the same time signaling the animal to feed.