Meeting Abstract

2.5  Jan. 4  Effects of fasting on growth hormone/insulin-like growth factor I axis in the tilapia, Oreochromis mossambicus FOX, B.K.*; RILEY, L.G.; PIERCE, A.L.; HIRANO, T.; GRAU, E.G.; University of Hawaii, Manoa; University of Hawaii, Manoa; University of Hawaii, Manoa; University of Hawaii, Manoa; University of Hawaii, Manoa kaifox@hotmail.com

Effects of fasting on the growth hormone/insulin-like growth factor I (GH/IGF-I) axis were examined in Mozambique tilapia acclimated to fresh water (FW) or seawater (SW). Fasting of FW tilapia for 2 weeks water produced significant reductions in body weight and in specific growth rate. Fasting of FW fish also significantly reduced plasma IGF-I, but had no effect on plasma GH or glucose. In SW fish, fasting for 4 weeks also significantly reduced body weight and specific growth rate. Plasma GH and pituitary GH mRNA levels were significantly elevated in fasted fish, while plasma glucose, IGF-I and hepatic IGF-I mRNA levels were significantly reduced. Plasma GH and IGF-I were significantly and negatively correlated in fasted SW fish. Fasting was without effect on hepatic GH receptor (GHR) mRNA levels in SW fish. The fact that fasting elicited increases in GH and decreases in IGF-I production without affecting GHR expression suggests a possible development of GH resistance in SW tilapia. These results suggest potentially disparate responses in the GH/IGF-I/GHR system during fasting between FW and SW-acclimated tilapia. Inasmuch as GH plays important roles in SW acclimation in the tilapia, fasting may affect the GH/IGF-I axis in SW tilapia more profoundly than in FW fish. We have recently identified the second GHR (GHR-2) in the tilapia. The effects of fasting and re-feeding on expression of the two GHRs will also be presented. Supported by grants from NSF (IOB 04-17250 and 05-17769).