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

Abstract

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 °C, fish subjected to an acute 15 min confinement stress at 25 and 30 °C, and fish fed 100 mg cortisol/kg feed. Plasma IGF-I concentrations were higher at 25 and 30 °C than at 20 °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 °C where a 33-kDa IGFBP was significantly reduced. After a 15 min low-water stress at 25 °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 °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.