Abstract
Dietary fish oils, enriched with wโ3 fatty acids (e.g., MaxEPA fish oil), inhibit lipogenesis and have a marked hypotriglyceridemic effect in man and experimental animals. Dietary wโ3 fatty acids also reduce adipose tissue trophic growth in rats. To understand the metabolic basis for this, we measured the effect of fish oil feeding upon rat plasma triglyceride concentration, fat pad mass, fat cell size, fat cell lipolysis, as well as lipoprotein binding to adipocyte plasma membranes. In adolescent (250 g) male Wistar rats fed 20% (w/w) fish oil supplemented diets for 3 weeks, plasma triglyceride levels and epididymal and perirenal fat pad mass were significantly (P<0.005) reduced compared to pairโfed controls given 20% lard diets. These differences in fat pad mass between the diets were greater than differences in whole animal mass or in the mass of livers, testes, kidneys, spleens, or hearts. Isoproternolโstimulated lipolvsis was significantly (P < 0.005) higher in fish oil fed rats than in pairโfed controls. In young (100 g) rats plasma triglyceride levels were 10 times lower in the fish oil fed group after 5 weeks as compared to the lardโfed controls. This was accompanied by a reduction in epididymal and perirenal fat pad mass as well as a 2โ3โfold decrease in adipocyte volumes; there was no significant difference between the two groups in fat cell number in each region. Plasma membranes of epididymal adipocytes from fish oil fed rats bound significantly (P < 0.001) less HDL1 than the lardโfed rats, possibly as a result of a reduction in fat cell size and/or alteration of plasma membrane structure. Thus in both young and old rats, the reduction in plasma triglyceride concentration in conjunction with increased hormoneโstimulated lipolysis may explain in part the selective reduction in adipose tissue trophic growth accompanying fish oil consumption.