Journal of Lipid Research, Vol 20, 857-864, Copyright © 1979 by Lipid Research, Inc.
Onset of genetic obesity in the absence of hyperphagia during the first week of life in the Zucker rat (fa/fa)
A Boulange, E Planche and P de Gasquet
The aim of this study was to discover which of three major abnormalities of
the genetically obese Zucker rat (fa/fa), namely hyperphagia, excess
adiposity, and hyperlipidemia, is the first to appear prior to manifest
obesity, i.e., before weaning. Suckling fa/fa rats, bred from heterozygous
parents, were detected by sizing fat cells obtained from an inguinal fat
pad biopsy. Cell hypertrophy was observed in fa/fa rats, compared to
Fa/-littermates of the same sex, as soon as 5-7 days after birth.
Prediction of fa/fa genotype at this age by this method was assessed using
a series of 80 pups and proved to be totally successful. The identity of
the "predicted" obese pups was confirmed morphologically at 6 weeks of age.
Food (milk) intake was estimated from water turnover rates determined on 86
pups aged 2-8 days using tritiated water. The results show that 7-day-old
fa/fa rats had heavier inguinal fat pads with larger adipocytes and higher
lipoprotein lipase activity than their lean controls. There was no genotype
effect on water intake adjusted to body weight during the first week of
life. Moreover weight of stomach contents and triglyceridemia were similar
in all animals at 7 days. These results show that excess adiposity develops
in the fa/fa rat during the first week of life, before hypertriglyceridemia
and hyperphagia, and raises the question of whether this adiposity results
from a defect in energy expenditure or an abnormality of fat cell storage
capacity, or both.