|Document Type:||Journal Article|
|Title:||Regulation of growth and metabolism by insulin family peptides in salmon|
|Author:||Walton W. Dickhoff|
The adaptive significance of insulin and insulin-like growth factor-I (IGF) in salmonids is their coordinated regulation of seasonal growth cycles. Their metabolic actions, seasonal blood concentrations, and association with plasma-binding proteins argue that insulin should dominate control of metabolism in winter, whereas IGF should dominate growth regulation during the major period of protein and bone growth in spring and summer.
ACTIONS: although both insulin and IGF stimulate protein and bone growth, insulin is lipogenic, whereas IGF is lipolytic and mitogenic. Thus, energy gained from infrequent feeding during winter at low temperature is best stored as fat (directed by insulin) rather than protein and bone.
SEASONAL BLOOD LEVELS: Plasma insulin is relatively high in fed fish during winter, IGF is low in winter and increases in spring. The vernal increase in IGF is probably due in part to associated increases in growth hormone and thyroid hormones.
PLASMA BINDING: Plasma binding of IGF buffers changes in free IGF levels, whereas insulin is unbound, which allows insulin to act rapidly in response to feeding. IGF responds slowly to sustained feeding that would be typical of spring/summer.
Abstracts: Annual Meeting, 6-10 January 1999