Experimental lipid storage myopathy. A quantitative ultrastructural and biochemical study.

A lipid storage myopathy was induced in rats treated with daily doses of 2.5 g/kg brominated vegetable oil. As in human lipid storage myopathies, type I fibers were selectively severely affected, the lipid deposits were surrounded by mitochondria and the mitochondrial fraction of the affected fibers was increased. The oxidation of [U-14C]palmitate, [1(-14)C]octanoate and beta-[3(-14)C]hydroxybutyrate was significantly depressed but [1(-14)C]palmitate, as well as labeled pyruvate and succinate were oxidized at normal rates. The activities of long-chain, medium-chain and short-chain carnitine acyltransferases and the muscle carnitine levels were normal. The lipid storage is attributed to impaired beta oxidation of medium-chain and short-chain fatty acyl residues. An approach to the investigation of those human lipid storage myopathies not due to defects in the carnitine system is suggested.