Effects of fasting on growth hormone, growth hormone receptor, and insulin-like growth factor-I axis in seawater-acclimated tilapia, Oreochromis mossambicus.

Effects of fasting on the growth hormone (GH)--growth hormone receptor (GHR)-insulin-like growth factor-I (IGF-I) axis were characterized in seawater-acclimated tilapia (Oreochromis mossambicus). Fasting for 4 weeks resulted in significant reductions in body weight and specific growth rate. Plasma GH and pituitary GH mRNA levels were significantly elevated in fasted fish, whereas significant reductions were observed in plasma IGF-I and hepatic IGF-I mRNA levels. There was a significant negative correlation between plasma levels of GH and IGF-I in the fasted fish. No effect of fasting was observed on hepatic GHR mRNA levels. Plasma glucose levels were reduced significantly in fasted fish. The fact that fasting elicited increases in GH and decreases in IGF-I production without affecting GHR expression indicates a possible development of GH resistance.