Title:
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A study of retinal pigment epithelial dystrophy (RPED) in dogs : with special reference to aspects of plasma lipid metabolism
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Retinal pigment epithelial dystrophy (RPED) is a progressive retinal
degeneration which occurs in a number of breeds of dog. It is characterised primarily
by the accumulation of abnormal lipofuscin-like pigment granules within retinal pigment
epithelial (RPE) cells of the tapetal fundus. Similar lipopigments accumulate in the RPE
in man in a range of diseases and during normal ageing. It is believed that they may
result from the incomplete degradation of phagocytosed photoreceptor outer segment
membranes and that autoxidative processes and abnormalities in lipid metabolism may
be important in their formation. The purpose of this study was to examine these
hypotheses, primarily through a study of the Briard dog, a breed in which RPED is
particularly prevalent.
The RPE lipopigment from affected dogs was analysed and compared with
similar pigments from RPE diseases in other species. Lipid and lipoprotein metabolism
and plasma antioxidants were studied in normal Briard dogs and in RPED affected
dogs of several breeds. The influence of a number of factors on canine RPE in vitro
were investigated.
Breed and species variation in RPE lipopigments were demonstrated and the
pigments that accumulate in RPED were partially characterised. A primary
hypercholesterolaemia was demonstrated in Briard dogs and this was further
characterised by plasma lipoprotein electrophoresis and precipitation, and
apolipoprotein analysis. The results of these lipoprotein and apolipoprotein studies
were consistent with the findings of studies of hyperlipidaemia in human retinitis
pigmentosa. Abnormalities were also demonstrated in the plasma antioxidants of RPED
affected dogs. The studies of canine RPE in vitro demonstrated the effects of a number
of factors on the behaviour of these cells in culture. The use of such culture techniques
may represent a useful method for further investigation of the initial hypotheses in the
light of the findings of this project
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