The distribution and lipid composition of ultracentrifugally separated lipoproteins of young and old rat plasma.

The lipoproteins of young and old Wistar rats differ markedly in distribution and chemical composition. The major differences are: (1) the presence of high levels of free and esterified cholesterol, triglycerides and free fatty acids in the lipoproteins of old rat plasma when lipids are analyzed/100 ml of plasma. However, the ratio of total cholesterol to protein mass indicates the presence of comparable cholesterol pools in all lipoprotein fractions of young and old rats excepting the d 1.063--1.21 fraction where a higher cholesterol pool in old rats is indicated. (2) The amount of sphingomyelin increases in lipoprotein fractions of old rat plasma thereby actually decreasing the lecithin/sphingomyelin ratio in these plasma fractions. (2) Unsaturated fatty acids predominate in young rat plasma lipoproteins, and saturated fatty acids predominate in old rat lipoprotein fractions. The ratio of polyunsaturated (linoleic, linolenic, arachidonic) to saturated (palmitic, stearic) fatty acids in young rat sera was 0.89 and in old rat sera, 0.55.