Modified lipoprotein lipase activities, rates of lipogenesis, and lipolysis as factors leading to lipid depletion in C57BL mice bearing the preputial gland tumor, ESR-586

Abstract

The biochemical basis for the observed depletion of adipose tissue in C57BL mice bearing a transplantable nonmetastasizing preputial gland tumor, ESR-586, has been investigated. The results have shown that there are a number of significant changes in both deposition and mobilization of lipid as the tumor grows. The first change, before the tumor reached 2 g, was a decline in the activity of adipose tissue lipoprotein lipase to levels normally found in starved animals. This was accompanied by a slight increase in lipoprotein lipase activity in heart and appearance of substantial activity in large tumors. Together, these would result in impaired uptake of exogenous fatty acids by adipose tissue, and dietary lipid would be directed away from storage. This was followed by a marked decline in endogenous lipid synthesis in adipose tissue which commenced when the tumor weighed between 2 and 3 g, as measured in vivo by the incorporation of radioactivity into lipid from tritiated water. The basal rate of lipolysis was enhanced 2-fold in epididymal fat pads from mice bearing tumors that weighed between 2 and 4 g, although there was no difference in the epinephrine-stimulated activity.