MATERIALS AND METHODS

Animals. C57 BL/Ks mdblmdb mice of both sexes, homozygous for the two genes db and m were used. Two breeding pairs were kindly supplied by Dr. DL Coleman (Jackson Laboratory, Bar Harbor, Maine), and a colony was derived from them in our laboratories, using a random breeding system. Controls were age-and sexmatched C57 BL/Ks++/++ mice, except for a few experiments carried out with mice before weaning, in which controls were the black nondiabetic littermates, a mix of mdb/++ and++/++ genotypes. After weaning, mice were fed ad libitum with UAR laboratory chow (Villemoisson, Epinay/Orge, France) containing 3% fat, 17% protein, and 59% carbohydrate until the time of experiment (between 9 and 11 AM). Animals were housed at 23OC with a 12-h dark-light cycle. All mice were weaned at 3 wk of age. In vivo Zipogenesis. Mice were anesthetized with an