Association of fat cell size and paracrine growth factors in development of hyperplastic obesity

Inguinal, epididymal, and retroperitoneal adipose tissue from lean and obes e Zucker rats, 3-15 wk of age, was used to determine the association among adipocyte size distribution, the presence of paracrine growth factors in ad ipose tissue, and subsequent changes in adipocyte number. For each specific depot and time point, obese rats had a greater percentage of large adipocy tes than did lean rats. A positive correlation (P < 0.02) was found in obes e rats between the percentage of inguinal and epididymal adipocytes in the 140- to 180-mu m size range and the ability of conditioned medium prepared from these depots to stimulate cellular proliferation in a bioassay system utilizing preadipocytes from inguinal fat pads of normal rats. Proliferativ e activity of the conditioned medium from all depots in obese rats was posi tively correlated (P < 0.01) to subsequent changes in fat cell number. The data presented here for the inguinal and epididymal depot of obese Zucker r ats are consistent with the hypothesis that enlarged adipocytes secrete gro wth factors that induce preadipocyte proliferation.