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Zucker Fatty Rats


Crl:ZUC(Orl)-Lepr (outbred)


Research applications

· Obesity

Strain origin

The spontaneous mutation "obese" (Fatty) was found in 1961 in the 13 M rat stock of Sherman and Merck, by Dr. Lois Zucker, Harriet Bird Memorial Laboratory, Stow, MA, USA. Zucker, LM and Zucker, TF (1961), J. Hered., 52, 275. The strain was introduced to Orléans at CSEAL, France in 1970 ; then transferred to Charles River Laboratories France in 1991.

· Model of human early-onset, hyperplastic - hypertrophic obesity and insulin resistance · Model of human NIDDM · Hypertension



Strain characteristics

· Obesity is evident at 5 weeks and may be noted as early as 3 weeks of age. By 14 weeks of age, their body composition is over 40 percent lipid and at 40 weeks of age, fa/fa rats weigh almost double as much as normal fa/+ littermates. Restricted feeding does not affect obesity. Feeding sucrose increases the level of lipogenesis in fa/fa rats. Obesity is unusual in the fact that fat cell proliferation occurs beyond the normal developmental period. It is of the hypertrophic-hyperplastic type involving an increase in both number and size of the adipocytes. · Significantly hyperphagic compared to lean littermates as early as 17 days of age and during periods of rapid growth. The obese Zucker rats' hyperphagia is not necessary for expression of the obese syndrome. · Hyperlipemia found after weaning, and increases with age. Total fatty acid serum content of mutants reaches tenfold levels of non-obese fa/+ rats. · Mean arterial pressure for obese (fatty) Zucker rats is significantly greater than in the lean Zucker rat and the Lewis rat. The greater blood pressure in the obese rats was not dependent on hyperphagia or increased body weight per se since moderate caloric restriction, achieved by pair-feeding with lean rats, decreased weight gain but did not attenuate hypertension. Pair-fed obese rats retained less sodium than lean control rats, suggesting that greater blood pressure in the obese rats is not a consequence of increased renal retention of sodium. A unique feature of the Zucker strain is that the increased blood pressure appears to be specifically associated with the obese genotype. Fatty rats do not develop a premature atherosclerosis. · Obese Zucker rats are hyperinsulinemic, both in the fed state and in response to oral glucose. Skeletal muscle of the Zucker fa/fa rat is highly insulin resistant, with depressed basal and insulin-stimulated glucose transport. Obese Zucker rats exhibit severe hepatic as well as peripheral insulin resistance. Moderate diabeteslike microvascular changes were reported consisting of decreased plantar muscle capillary density and increased basement membrane thickness in obese compared to lean Zucker rats. · Abnormal brain neuropeptide physiology related to a fa gene-dosage effect. Obese (fa/fa) and heterozygous lean (+/fa) Zucker rats have lower than normal brain insulin content when compared to homozygous lean (+/+) animals, particularly in the olfactory bulb.

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Zucker Fatty Rats

Growth Curve

800 780 760 740 720 700 680 660 640 620 600 580 560 540 520 500 480 460 440 420 400 380 360 340 320 300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0


n = 10 Date = 2001 Breeding Unit = B42, France


Female Lean Male


Lean Female


















Growth curves may vary slightly from room to room

Breeding system

Mating system* Litter size at birth Gestation period Weaning age Watering system Bedding Diet Room temperature Light cycle Harem - 1 homozygous male and 5 heterozygous females 8-9 22 - 23 days 22 - 25 days Filtered (0.1 µm) and UV treatment Bottle system Sawdust bedding, autoclaved Rodent VRF1, autoclaved 21 ± 3 °C 12 ­ 12 (6:00 pm ­ 6:00 am)

*Colony management

fa/fa males are only occasionally fertile while fa/fa females are uniformly sterile. Therefore, heterozygotes fa/+ female breeders are used resulting in 50% fa/fa and 50% fa/+ progeny. Phenotypic identification of fa/fa models occurs at 3 weeks of age.

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Zucker Fatty

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