12-O-tetradecanoylphorbol-13-acetate (TPA) stimulates the adipose conversion of piglet preadipocytes in primary culture

The effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) were analyzed on the proliferation and differentiation of cultured porcine preadipocytes. In both chemically-defined and serum-containing media, short term treatment ( 2 days), either during the growth phase or from confluence, significantly e nhanced cell proliferation, as assessed by tritiated thymidine incorporatio n and protein content assay. Addition of TPA during the growth phase in ser um-free medium had no effect on lipoprotein lipase (LPL), glycerol 3-phosph ate dehydrogenase (GPDH) and malic enzyme (ME) activities after 14 days of culture. By contrast, similar treatments in serum-containing medium signifi cantly increased all these enzyme activities. Addition of TPA from confluen ce in both media stimulated LPL activity on day 14 as well as ME activity o n day 17. These results were confirmed by morphologic studies. In conclusio n, this study demonstrates that a short stimulation of the protein kinase C pathway can enhance the differentiation of porcine preadipocytes. Such a p ositive effect is however dependent on the time of TPA addition as well as the culture conditions, indicating a complex regulation of the protein kina se C pathway in this cell type.