1. The aim of this investigation was to ascertain of a variety of obese rodents whether the primary cause of fat cell enlargement lay in the fat cell itself, or in its environment. Rodents studied were the mutant mice ‘diabetic’ (
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or
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hybrids (NZO x BALB/c) made by mating the strains acting as donors of obese or lean fat. Transplantation of fat between lean BIO 4.22 hamsters and obese BIO 4.24 hamsters was possible because these had common histocompatability antigens. 4. In all the forms of murine obesity studied, ‘lean’ fat cells enlarged in an obese recipient to the size typical of cells in ‘obese’ fat whilst ‘obese’ fat cells shrunk in a lean recipient to, at least, the size typical of ‘lean’ fat. Lean hamster fat cells also enlarged in an ‘obese’ environment and ‘obese ’ hamster cells shrunk in a 'lean’ environment. 5. Environment therefore contributes to the determination of fat cell size in all the rodents studied, and in several rodents (
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,
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Determination of β3-Adrenoceptor Mediated Lipolysis in Human Fat Cells
