[14C]acetate metabolism in the peripheral nervous system.

Lipid biosynthesis was studied by incorporation of [14C]acetate into different compartments of rat sciatic nerve during development, degeneration and regeneration. Acetate incorporation was over three times higher in the sciatic endoneurium (desheathed nerve) than in epi- and perineurium. The endoneurium contained much higher contents of radioactively labeled membrane lipids (cholesterol and phospholipids) than did the epi- and perineurium (mainly triacylglycerol), indicating a benefit of utilization of endoneurium in the study of the metabolic derangements of peripheral nerve lipids. When 3H2O was used as a precursor, no incorporation was found. Endoneurial lipid biosynthesis from [14C]acetate decreased rapidly as myelination proceeded. After 4 months, the decrease continued but at a much slower rate. The total acetate incorporation found in endoneurial lipids of 6-month-old rats was predominantly in the free fatty acid fraction (40%), but was only 5% of that found in 10-day-old rats, demonstrating the importance of age-matched controls for metabolic studies of diseased nerve. During Wallerian degeneration, a decreased acetate incorporation into endoneurial lipids was observed as early as 2 days after crush injury. The profile of labeled lipids in developing and degenerating nerve revealed that the rate of lipogenesis did not change to the same extent for each lipid subclass. Cholesterol biosynthesis appeared to be the most sensitive. During regeneration, an increase in the uptake of [14C]acetate and an altered profile of labeled lipids demonstrated that the metabolic state of adult peripheral nerve, which is normally relatively inactive, can be modified by an exogenous factor such as crush injury.