Microsomal Lipids of Various Tissues in the Rat. ∗

Considerable data indicates the functional importance of lipid components of protoplasm in normal, physiological activities of cells and tissues (Fleischer and Klounen(1); Gray and MacFarlane(2); Johnson and Albert(3). Believing that the fundamental lesion involved in the malfunction of organs and tissues must lie within the functional mechanisms of constituent cells, it is pertinent that a base line of lipid constituents in normal cells must be accurately defined by quantitative analysis.

The lipid composition of rat liver cell sap has been described by Getz(4). MacFarlane et al(5) have described the fatty acids of phospholipids from mitochondria and microsomes of rat liver. A study similar to that herein described has recently been published by Getz et al(6).

Materials and methods. Sprague-Dawley rats 300–400 g fed standard purina laboratory chow were fasted for 24 hours and sacrificed by decapitation. Liver was perfused via the dorsal aorta with Locke's solution and homogenized in cold, 0.25 M sucrose(7).

Cell debris, mitochondria and nuclei were separated from soluble phase proteins and microsomes by low temperature centrifugation at 11,000 × g for 15 minutes. Fatty layer on the surface of supernatant was aspirated and treated separately. Microsomes were isolated by centrifugation of remaining supernatant in the Spinco “L”at 105,000 × g for 1 hour, washed 3 times with 0.25 M sucrose, lyophilized and subsequently extracted.

Microsomes were extracted overnight in chloroform-methanol (2:1 v/v) and washed according to Folch et al(8). Total lipid/extract was determined gravimetrically and a sample (300–400 mg) diluted in 10 ml of hexane, placed on a 16 gram silicic acid (Unisil 200–325 mesh, Clarkson Chem. Co., Williamsport, Pa.) column apparatus described by Hirsh and Ahrens(9). Lipid classes were eluted in accordance with a scheme devised by E. C. Horning, modified by D. A. Turner, Nat. Inst.