REGULATION OF LIPID-METABOLISM IN POIKILOTHERMIC VERTEBRATES

Patterns of lipid storage and utilization reflect the special life his tories of the animal group. Poikilothermic vertebrates (fish, amphibia ns, reptiles) have evolved a number of life history patterns (smoltifi cation, metamorphosis, hibernation) which present problems for lipid s torage regulation. A general theme among poikilotherms is to store lip ids among several sites (mesenteric fat, liver, muscle) as opposed to a single depot type (adipose tissue) as in homeotherms; lipids are sto red primarily as triacylglycerols, but various other lipid classes als o are stored and constituent fatty acids tend to be more complex (long er chain, polyunsaturated). Lipid storage is influenced by de novo lip id synthesis and by lipid deposition from various plasma lipoproteins. Lipid accumulation generally occurs in most poikilotherms during peri ods of feeding when plasma insulin levels are elevated. Lipid mobiliza tion is controlled by an intracellular lipase enzyme. Lipid depletion occurs during transitional and non-feeding periods and is especially a pparent during salmonid smoltification and amphibian metamorphosis.