The Lipids of Faeces

Fractionation schemes have been devised for separation of the major classes from unsaponified human and rat faecal lipids. A number of the shortcomings of some previous fractionation procedures have been overcome, notably by improved separation of acidic and non-acidic compounds, purification of bile acid and fatty acid fractions, isolation of sterols by silicic acid chromatography and further fractionation of other neutral lipids.
The fractionation procedures have been applied to faeces of rats injected intravenously with serum lipoprotein containing free and ester cholesterol labelled with 14c. Although activity levels in the lipid fractions were low, useful information was obtained, and the procedures are suitable for use in other tracer experiments involving excretion of active lipids in the faeces.
The following lipid classes were isolated from rat faeces: free fatty acids, free and conjugated bile acids, longchain alcohols and esters, hydrocarbons, free and esterified sterols and phospholipids. There was evidence for the presence of mono- and diglycerides.
Free fatty acids were inactive and constituted the major lipid class present; fatty acid soaps were absent. The complex bile acid mixture contained about two-thirds of the total faecal activity,in the tracer experiments; a small proportion of these acids was present in the conjugated form. Both free and esterified long-chain alcohols were present, and were inactive. Rat faeces contained both straight-chain and cyclic hydrocarbons; the latter were probably derived from dietary mineral oil, but es wis some evidence for the presence of steroidal hydrocarbons. Sterols were represented by coprostanol, cholesterol and sterols of similar polarity, by more polar sterols, and by esterified sterols. One-third of the total faecal activity was present in these components. The specific activity of the esterified sterols suggested that esters derived from serum cholesterol had been considerably diluted with inactive dietary sterol esters.