Cultured Mammary Epithelial Cells Secrete a Factor Which Suppresses Lipoprotein Lipase Production by 3T3-L1 Adipocytes

The enzyme lipoprotein lipase (LPL) is made in tissues which use plasma lipoprotein triglycerides either as a source of energy, e.g. muscle, or for storage, adipose tissue (Eckel, 1989). In rodents, LPL activity is low in the mammary gland and high in adipose tissue during pregnancy. At birth there are reciprocal changes with LPL activity in the mammary gland rising to very high levels while it is barely detectable in adipose tissues. This allows triglycerides to be diverted from storage in adipose tissue towards the production of milk fat (Hamosh et al., 1970; Jensen et al., 1994). However, LPL is synthesized by the adipocytes in the mammary gland (Jensen et al., 1991), raising the question: how are the same cell types in two different regions of the body controlled independently?