A preadipocyte clonal line has been established from porcine subcutaneous tissue. This line, designated PSPA, showed a fibroblastic phenotype and kept on growing under a preadipose condition even after reaching confluence. When confluent cultures were stimulated with insulin, dexamethasone, biotin, pantothenate, and octanoate, growth was arrested, and the cells exhibited a marked increase in lipogenesis. However, adipose conversion was not induced upon exposure of PSPA cells to a standard hormonal mixture of mouse 3T3-L1 cells, and they continued dividing as did the preadipocytes in growth-medium. By serially omitting each individual adipogenic agent from the PSPA differentiation medium, it was determined that octanoate was one of the most essential but the only factor able to induce growth arrest. Octanoate supplementation to 3T3-L1 medium increased the triglyceride accumulation of PSPA cells accompanied by growth arrest. Both RT-PCR and Western blot analysis supported the idea of octanoate as a potential agent with the antiproliferative activity requisite for porcine preadipocytes to enter terminal differentiation. (C) 2003 Elsevier Inc. All rights reserved.