The effect of temperature, stress, and cortisol on plasma IGF-I and IGFBPs in sunshine bass

The mechanisms through which stress and cortisol regulate insulin like growth factor-I (IGF-I) and insulin like growth factor binding proteins (IGFBPs) were studied in sunshine bass, by measuring plasma IGF-I and IGFBPs in fish maintained at 5, 10, 15, 20, 25, or 30 degrees C, fish subjected to an acute 15 min confinement stress at 25 and 30 degrees C, and fish fed 100 mg cortisol/kg feed. Plasma IGF-I concentrations were higher at 25 and 30 degrees C than at 20 degrees C and below. A 15 min confinement stress resulted in a decrease in IGF-I 2 h post-confinement. Plasma concentrations of IGFBP with molecular weights of 24, 28, and 33 kDa were similar for fish acclimated to different temperatures, except for 5 degrees C where a 33-kDa IGFBP was significantly reduced. After a 15 min low-water stress at 25 degrees C, a 33-kDa IGFBP was reduced and IGFBPs with molecular weights of 24 and 28 kDa were increased at 2 and 6 h, respectively. A 15 min low-water stress at 30 degrees C, resulted in no change in levels of a 33-kDa IGFBP over the 6-h recovery period. However, levels of a 24- and 28-kDa IGFBP were significantly increased at 2 and 6 h, respectively. A single feeding with 100 mg cortisol/kg feed increased plasma cortisol but did affect plasma concentrations of IGF-I or any of the three IGFBPs. Acute stress appears to result in a decrease in IGF-I, but the mechanism of the decrease does not appear to be caused by cortisol released during the stress.