Influence of arachidonate metabolite pathway on adipose differentiation was investigated using primary culture of adipocyte precursors in defined medium. Treatment of the cells with cyclooxygenase inhibitors stimulates adipose differentiation by at least 2-fold. Among the various arachidonate metabolites tested, only prostaglandin F2 alpha (PGF2 alpha) was found to inhibit the differentiation of adipocyte precursors in a dose dependent fashion. Other eicosanoids tested did not have any effect. A 50% inhibition of adipose differentiation was observed with a dose of PGF2 alpha of 3 x 10(-9)M to 7 x 10(-9)M according to the strain of rats used. Maximal inhibition occurred at PGF2 alpha concentrations equal or higher than 10(-8)M. PGF2 alpha inhibited not only the expression of late markers of adipose differentiation such as G3PDH and triglycerides accumulation but also the mRNA expression of early markers of adipose differentiation such as clone 154, lipoprotein lipase and ap2 gene. These results indicate that PGF2 alpha represents a physiological negative modulator of adipose differentiation.