Title: THE EFFECT OF TEMPERATURE, STRESS AND CORTISOL ON PLASMA IGF-I AND IGFBPS IN SUNSHINE BASS Authors
Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 23, 2006
Publication Date: November 18, 2006
Citation: Davis Jr, K.B., Peterson, B.C. 2006. The effect of temperature, stress and cortisol on plasma IGF-I and IGFBPS in sunshine bass. General and Comparative Endocrinology. 149:219-225. Interpretive Summary: Growth of fish is primarily regulated by hormones from the pituitary and the liver. Growth hormone from the pituitary stimulates the liver to synthesize and release insulin-like growth factors I and II. Somatic growth is thought to be primarily stimulated by IGF-I. This hormone is transported in the plasma by proteins called insulin-like growth factor binding proteins. Feeding and growth are both affected by the water temperature and both are decreased by stress to the fish. Plasma cortisol is a hormone secreted during stress and is thought to mediate many of the stress responses observed in fish including the decrease in feeding and growth. The effect of temperature, low-water confinement stress and dietary cortisol on IGF-I and the IGFBPs was studied in sunshine bass. Fish held in water temperatures of 25 and 30 'C had higher IGF-I concentrations than fish held at 20 'C and below and confinement at these high temperatures resulted in lower IGF-I levels two hours after the stress. Three IGFBPs were detected and were different among fish held at different temperatures only at the lowest temperature. Low-water confinement stress resulted in a decrease in the largest IGFBP and a decrease of the two smaller IGFBPs at 25 'C, however no change was apparent in fish stressed at 30 'C. A single feeding of 100 mg/kg of cortisol increased plasma cortisol but had no effect on plasma IGF-I or the IGFBPs. The change in IGF-I caused by stress is apparently not mediated by cortisol.
Technical 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 two hours 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 hours, respectively. A 15 min low-water stress at 30'C, resulted in no change in levels of a 33-kDa IGFBP over the six-hour recovery period. However, levels of a 24- and 28-kDa IGFBP were significantly increased at 2 and 6 hours, 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.