Abstract
1. Experiments are described whose results
indicate that the half-life of serum ¹⁴C-labelled
cholesterol in the rat was decreased
when the animals had been pre-fed a diet
containing unsaturated fat.
2. In most of these experiments there was also
an indication that the rate of biosynthesis
of cholesterol from acetate was increased
when the animals had been pre-fed such a
diet.
3. A proposed explanation for these phenomena
is that unsaturated fatty acids may combine
with cholesterol to form esters which are
metabolized more readily than are esters
formed with other fatty acids.
4. The isolation of a new Lifschútz chromogen
is described. The material was present in
human serum and leucocytes and in rat serum,
skin and liver. It was shown to be
identical with the 3ß-oleyl and linoleyl
esters of 7α-hydroxycholesterol.
5. The chemical synthesis of a series of 3ß-acyl
esters of 7α-hydroxycholesterol is
described in detail, as previously a method
has been reported only for the acetyl ester.
The physical and chromatographic
properties of the esters are tabulated.
6. The synthetic esters were used as substrates
for enzymic experiments. The results of
these experiments show that the cholesterol
esterase system of pancreas was effective
for both the hydrolysis and synthesis of the
esters, and that of liver for hydrolysis
only.
7. The esters were efficiently metabolized to
bile acids in vitro.
8. Attempts to produce the synthetic esters
either by enzymic oxidation or by autoxidatio
of cholesteryl esters were not successful.
9. A description is given of the curious changes
undergone by the esters on exposure to
ultraviolet light. The resultant changes
in structure are discussed.
10. A possible Ale for the naturally occurring
esters is suggested, whereby they may form
an alternative pathway in the production of
bile acids from cholesterol.
11. A hypothesis is described in which it is
proposed that the preferential oxidation of
certain cholesteryl esters to form esters
of 7α-hydroxycholesterol may explain the
effect of unsaturated fatty acids on
cholesterol turnover.
