Influence of paracrine factors on preadipocyte replication and differentiation.

Regional adipose tissue growth may be modulated by paracrine factors that influence preadipocyte replication and/or differentiation. To investigate this hypothesis, we have studied the effects of culture media conditioned by adipose microvascular endothelial cells, preadipocytes, or mature fat cells, on rat preadipocyte replication and differentiation in vitro. Endothelial cell-conditioned medium (ECCM) stimulated preadipocyte replication while medium conditioned by mature fat or preadipocytes had little effect. ECCM contained heat and trypsin sensitive polypeptides, with molecular masses in the 18-35 kDa range. Mature fat-conditioned medium, but not medium enriched with triacylglycerols, induced differentiation in about 50 percent of preadipocytes. This effect was greatly reduced in cells derived from genetically obese JCR:LA-corpulent (cp) rats compared to those derived from lean JCR:LA-cp or Sprague-Dawley rats. The present studies demonstrate the presence of paracrine factors which may play a role in regulating regional adipose tissue growth.