The effect of insulin on Delta 5 desaturation in hepG2 human hepatoma cells and L6 rat muscle myoblasts

In humans there is a correlation between the ratio of arachidonic acid (20: 4n-6) to cis 8,11,14 eicosatrienoic acid (20:3n-6) in skeletal muscle phosp holipids and insulin sensitivity. This has been interpreted as indicating a link between the activity of the Delta 5 desaturase enzyme and muscle insu lin sensitivity. The present study addressed the possibility that insulin r egulates Delta 5 desaturase activity using L6 rat myoblasts and hepG2 human hepatoma cells. Both cell lines responded to insulin by increasing the amo unt of D-[U-C-14] glucose incorporated into glycogen. In L6 cells, insulin stimulated cis 8,11,14 eicosatrienoic acid uptake and arachidonic acid prod uction but had no effect on the percentage conversion of cis 8,11,14 eicosa trienoic acid to arachidonic acid. In hepG2 cells, insulin had no effect on cis 8,11,14 eicosatrienoic acid uptake or arachidonic acid production. The se results suggest that insulin has no direct effect on Delta 5 desaturase activity in the liver but can alter arachidonic acid production in muscle b y altering substrate availability.