The feeding of perfluorodecanoic acid (PFDA) to male rats at a dietary concentration of 0.005% (w/w) for 7 days resulted in a marked increase in the activity of microsomal stearoyl-CoA desaturation in the liver. This increase in the overall desaturation activity was due to the induction of terminal desaturase among the components comprising the desaturation system. In contrast, PFDA inhibited desaturation invitro, seemingly due to interference with electron transport through the desaturation system. Accordingly, PFDA can be an inducer and also an inhibitor of Δ9-desaturation. PFDA feeding enhanced the conversion of radioactive stearic acid into oleic acid in the liver invivo, indicating that the induction of δ9-desaturase by PFDA functions invivo. PFDA feeding increased the mass of octadecenoic acid (C18:1) in the liver and the proportion of C18:1 in microsomal lipid. A highly significant linear correlation existed between the microsomal desaturase activity and the proportion of C18:1 in microsomal lipid when compared using rats in five different physiological states: control, PFDA-fed, p-chlorophenoxyisobutyric acid (clofibric acid)-fed, starved and starved/refed. These results suggest that the increase in the hepatic level of C18:1 caused by feeding of PFDA to rats can be explained by the common concept of regulation, i.e. the hepatic level of C18:1 is under the control of δ9-desaturase. The dietary administration of PFDA also increased the content of cytochrome P-450 and the activity of 7-ethoxycoumarin O-de-ethylase in the liver.

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Present address; Faculty of Pharmaceutical Sciences, Science University of Tokyo, 12 Ichigaya Funagawara-machi, Shinjuku-ku, Tokyo 162, Japan.