Abstract
Adult rats of various strains show small increases in the number of adipocytes in the epididymal (Epi) fat pad and large increases in the retroperitoneal (RP) fat depot when they are fed a high-fat, high-sugar diet ( HFS ). In the present study, radioautographic techniques are used to demonstrate that these increases result from replication and differentiation of adipocyte precursors. In addition, both in vivo and in vitro biochemical techniques are used to demonstrate that HFS -induced acceleration of DNA synthesis differs between Epi and RP depots. Measures of levels of incorporation of radiolabeled thymidine into DNA in rats fed HFS for 4 weeks reveal significant elevation in the RP depot but not in the Epi pad. Analysis of radioautographs indicates that formation of precursors may be accelerated in the RP depot as early as the first week of HFS -feeding. Results obtained from the in vitro biochemical assay are of interest with regard to possible clinical application since current in vivo techniques for quantitative assessment of precursor synthesis cannot be applied directly to the study of adipose tissue growth in man. While data obtained from the in vitro assay contains a relatively high degree of variation, the information it provides is in general agreement with that provided by the in vivo assay.
Highlights
Adult rats of various strains show small increases in kinase, an enzyme associated with DNA synthesis, is elthe number of adipocytes in the epididymal (Epi) fat pad and large increases in the retroperitoneal (RP) fat depot when they are fed a high-fat, high-sugar diet (HFS).In the present study, radioautographic techniqueasre used todemonstrate that these evated in the epididymal (Epi) pad of genetically obese Zucker rats during adulthood
Rates of DNA synthesis in Epi and RP fat depotswere compared in rats with continuous ad libitum access to a fattening dieMt. easures were made at several time points before significant differences in adipocyte hyperplasia normally appear
The animals showed a small drop in body weight and fat cellsize relative to controls on day 5, but the level of DNA synthesis measured at the time of injection may reflect an initial increase in body weight in response to HFS
Summary
Adult rats of various strains show small increases in kinase, an enzyme associated with DNA synthesis, is elthe number of adipocytes in the epididymal (Epi) fat pad and large increases in the retroperitoneal (RP) fat depot when they are fed a high-fat, high-sugar diet (HFS).In the present study, radioautographic techniqueasre used todemonstrate that these evated in the epididymal (Epi) pad of genetically obese Zucker rats during adulthood. Fauct, and Hirsch D e novo production of adipocytes in adult rsts 341 the RP depots of each of the four HFS-fed rats showed comparable numbers of labeled fat cells.
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