Demonstration of de novo production of adipocytes in adult rats by biochemical and radioautographic techniques.

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.