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In order to study how adipose conversion affects the extracellular environment, levels of extracellular matrix (ECM) proteins during differentiation were analyzed by 125I-labeled antibody binding to each specific primary antibody. When confluent bovine intramuscular preadipocytes (BIP) were stimulated with adipogenic medium, there was a significant accretion on the cell surface of type I-VI collagens, laminin and fibronectin, compared with undifferentiated cells. The deposition amount of ECM proteins had reached near maximal levels at an early stage of differentiation and lasted throughout the culture. However, the increasing manners were not all the same in these eight proteins. Type V and type VI collagen tended to show a transient decline after the rapid rise at the beginning of stimulation, and fibronectin instead, subsequently decreased. Further analysis by immunocytochemical staining showed that remodeling occurred in type V and VI collagen matrices during this period; extensive fibrillar networks seen at 10 d after stimulation were quite unlike that formed earlier. These specific increases and development of matrix during adipocyte differentiation imply some significance for organizing fat lobules in each ECM proteins, especially type V and VI collagens.

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