Lough, Alexander Kenneth

2018-05-22T12:44:06Z

2018-05-22T12:44:06Z

1955

The presence of cholesterol in egg yolk was first shown by Lecanu (1329). Gobley (1346) and Menozzi (1903) examined the cholesterol prepared from this source and found it to be identical viith that from gall-stones and bile. Although other sterols have been found in egg yolk it has been shown that these are present in relatively small amount, Ergosterol separated from 'egg cholesterol1 (Windaus and Stange, 1936) was shown by ultraviolet absorp¬ tion analysis to constitute about 0,1% of the total sterol (Schoanheimer and Dam, 1932; Windaus and Stange, 1936; Skarzynski, 1936). Skarzynski (1936) found the sterol content of the agg to include 3-4% dihydrocholesterol and showed that this proportion did not change after 20 days' incubation. Stokes, Fish and Hickey (1953) employing counter-current distribution methods observed that 95% of the digitonin precipitable material from the egg appeared to consist of cholesterol.

The existence of a high concentration of cholesterol (more than 1%) in egg yolk has aroused considerable interest and many workers have been attracted to problems concerning the metabolism of this substance during embryonic development Although much of the early work has been vitiated by the use of / of crude analytical techniques or by failure to take into account the variation in total cholesterol from egg to egg, it is fairly well established that little net change occurs in the cholesterol content of the egg after incubation (Dam, I9285 19295 Skarzynski, 1936; Stokes, Fish and Hickay, 1953),

Kusui (1929) showed that apart from stray traces cholesterol in the incubated egg is confined to embryo and yolk.

The distribution of total cholesterol between embryo and yolk has interested two groups of workers (Roffo and Izaretti, 1926| Serono, Montezoraolo and Balboni, 1936) but in both cases the work involved the analysis of only one egg at each of several stages of incubation. It is therefore not surprising that the conclusions obtained show wide disagreement.

Mueller (1915) first observed that esterified cholesterol, which accounts for about 10% of the total cholesterol in the egg at the beginning of incubation increases to over 40% at hatching. Although later workers (Thannhauser and Schaber, 1923; Kusui, 19295 Dam, 1929) confirmed Mueller's (1915) conclusion, little attempt has been made to determine the distribution of ester cholesterol in the incubated egg. Kusui (1929) studied free and esterified cholesterol in both embryo and yolk but his results can be of little significance since the entire investigation was made on a total of only six eggs. It has, however, been shown (Entenman, Lorena and Ghaikoff, 1940) that the liver of the newly hatched chick contains as much as 7% cholesterol (wet weight tissue) of which some 90% is esterified, and that this high concentration of cholesterol diminishes to less than 1% within two weeks following hatching.

Bntenman et al» (1940) also observed a high concen¬ tration of cholesterol in the blood of the newly hatched chick, and a decrease of some 60% during the first two weeks of life. These results are, however, in disagreement with the observations of Zorn and Dalton (1936) who found a hypereholesterolaeraia in the blood of the 18 day embryo, a | disappearance of this condition at hatching and a rise in blood total cholesterol two days after hatching.

In recent years it has become evident that at least in mammals and more particularly in man, cholesterol is transported in the blood serum in the form of two main lipoprotein fractions which migrate electrophoretieally near the α globulins and the(Β globulins respectively. This work has been collected and reviewed by Cohn (1953). The first work of this kind to be done on birds was reported by McKinley, Oliver, Maw end Common (1953) who found two distinct lipid components in the serum of immature pullets by the application of lipid staining techniques to paper electrophoresis diagrams.

The work reported in this thesis comprised:

(i) An investigation of the changes in free and ester cholesterol in the embryo and the remainder of the egg throughout the course of incubation,

(ii) A study of the lipid changes in the developing chick livers which seemed of interest in view of the observation by Enienman et al. (1940) that the liver of the newly hatched chick is rich in cholesterol esters.

(iii) An attempt to locate the site, or sites, of a cholesterol ester synthesizing system in the incubated egg.

(iv) A re-investigation of the changes in blood cholesterol concentration during embryonic development and in the newly hatched chick,

(v) A study of protein-bound cholesterol in the serum of the late- embryo and the newly hatched chick

http://hdl.handle.net/1842/30401

The University of Edinburgh

Annexe Thesis Digitisation Project 2018 Block 19

Cholesterol metabolism in the embryonated hen egg

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy