Influence of Dietary Protein and Fat on Lipogenesis and Enzymatic Activity in Pig Adipose Tissue

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Abstract
Biopsy samples of porcine adipose tissue were used to investigate the effect of dietary protein and fat levels on in vitro lipogenesis as measured by the incorporation of glucose-U-14C into fatty acids. In addition, the activities of the pentose pathway dehydrogenases, malic enzyme and citrate cleavage enzyme were also studied. Carcass measurements were made on all animals to determine whether in vitro rates of lipogenesis were indicative of total body fat. Increasing the level of dietary fat (corn oil) from 1 to 13% markedly depressed (60 to 70%) in vitro lipogenesis but increased measurements of body fat, presumably due to the direct deposition of dietary fat. Increasing the protein level of the diet from 12 to 24% significantly reduced in vitro lipogenesis, and carcass measurements suggested a reduction in body fat in one experiment, but protein level had no significant effect on lipogenesis or measurements of body fat in a second experiment. The activities of the pentose pathway dehydrogenases and malic enzyme were significantly depressed in adipose tissue homogenates of pigs fed the high fat diets. The activity of malic enzyme appeared to be closely related to the rate of lipogenesis. The findings are discussed in light of present knowledge of the control of fat synthesis and their relevance to current investigations of carcass fat content of pigs.