Phenotypic variability in unweaned 3-week-old Zucker rats.

At 3 weeks of age, Zucker rats could not be classified as normal or obese according to body or liver weight. On the other hand, determination of subcutaneous adipose tissue weight per 100 grams of body weight permitted both phenotypes to be distinguished, provided that the growth variations particular to each litter were taken into account. Rats whose future obesity is predictable using this method, have significantly elevated serum levels of triacylglycerols, total cholesterol and phospholipids. However, further analysis of these values indicated that in fact there were two subgroups of both obese and non-obese rats, i.e., those which had elevated serum lipid levels and those which did not.