Free and esterified sterols have been isolated from whole rats. These animals were adult males of the Wistar strain fed on a semi-synthetic diet after wean'ng. The mean concentration of free sterols was 1.31 mg/g of body weight; of esterified sterols: 0.46 mg/g. The percentage of esterification was 25%. Free as well as esterified sterols were analysed by gas chromatography. Cholesterol represented 98% of free sterols, but only 37% of esterified sterols. Other esterified sterols were essentially precursors of biosynthetic cholesterol: lathosterol (36%), methostenol (13%), dihydrolanosterol (12%). Moreover, the percentage of esterification was 12% for cholesterol and 88% for precursor sterols. Similar determinations and analyses have been carried out in 23 rat organs or tissues. The concentration of free sterols varied: plasma 0.19 mg/g; cutaneous tissu 1.34 mg/g; kidneys 3.3 mg/g; spinal cord 40 mg/g. The range of values was also large for esterified sterols: o for red cells, 1.94 mg/g for cutaneous tissue, 25 mg/g for adrenals. Various percentages of esterification were found; for instance o% (red cells), 5.5% (testes), 37% (liver), 55%) (cutaneous tissue), 76% (adrenals). It was calculated that 85% of the esterified sterols in whole rat were contained in the cutaneous tissue. Gas chromatographic analysis showed that cholesterol was the essential sterol (95-99%) in the free fraction of each organ and that the precursor sterol most generally detected in this fraction was methostenol. Results concerning the esterified fraction distinguished cutaneous tissue from other organs. In this tissue the distribution was: cholesterol 21%, lathosterol 46%, methostenol 20%, dihydrolanosterol 9%. In other organs, the mean percentage of esterified precursor sterols was 18%,. Lathosterol and methostenol were the esterified precursor sterols most often detected. In most organs, except liver, plasma, adrenals, the percentage of esterification was 3-10 times greater for precursor sterols than for cholesterol. These results must be interpreted taking into account the sterol composition of the diet. Thus a sterol, probably β-sitosterol, is consistently found in animal tissues in minute amount. © 1969.
