Meeting Abstract

2.1  Jan. 4  Post-prandial response of insulin, IGF-I, and IGFBPs in fasted coho salmon. BECKMAN, B.R.*; SHIMIZU, M.; NOAA Fisheries; University of Hokkaido Brian.Beckman@NOAA.gov

Insulin and insulin-like growth factor-I are peptide hormones that apparently arose from a common ancestral gene. Both IGF-I and insulin are important components of the endocrine growth regulation system. To better understand how these structurally similar hormones interact with nutritional signals to regulate fish growth we undertook an experiment featuring fasting and re-feeding. Coho salmon juveniles were fasted either over-night, for one week, or for three weeks. Subsequently, half of the fish from each fasting group were fed. The post-prandial response of fish from all treatments was followed at four hour time intervals through a 24 hour cycle by collecting terminal blood samples from a sub-set of fish. Plasma levels of insulin, IGF-I, IGFBP1, and 41 k IGFBP (putative IGFBP3) were assessed from these fish. Basal levels of insulin were similar for fish from all three fasting treatments, post-prandial increases in insulin were graded according to fasting status (greatest response in fish fasted the least amount of time). In contrast, basal levels of IGF-I varied among fasting treatments with highest levels in fish fasted only overnight. Post-prandial changes in IGF-I were slight. The differential response of IGF-I and insulin to feeding following a fast is likely due to differences in how these hormones are produced, stored, and cleared. IGF-I is secreted constitutively after production and is retained in the blood by IGFBPs. In contrast, insulin is stored after production and secreted in response to a cascade of signals following feeding. However, insulin is rapidly cleared from the blood after secretion while clearance of IGF-I is retarded by the IGFBPs. These data help reveal the diversity of mechanisms regulating endocrine actions.