Lipid release by liver slices

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Abstract
Slices were prepared from livers of rats which had received an intravenous injection of 1-C14-palmitate 20 min prior to the removal of the livers. The labeled acids were found predominantly in the neutral fat fraction (61%), smaller amounts (32%) in the phospholipids, and only 6% as unesterified fatty acids. When such slices were incubated in salt solutions, labeled lipids were released into the medium. This release could be promoted by the use of blood serum as medium or by the addition of α- or ß-lipoproteins to the salt solutions. Serum albumin was less effective. Release came rapidly to an end when an equilibrium was established between the liver and the medium and could be renewed by replacing the medium with a fresh protein solution. When unlabeled liver slices were incubated in media with labeled triglycerides, the labeled compound was assimilated by the liver. The presence of blood serum and lipoproteins increased the relative contribution of the phospholipids to the lipids released. Serum albumin and blood serum promoted the release of free fatty acids by the liver. The physiological significance of this latter process is discussed.