Effect of Meal-Feeding on Insulin Sensitivity and Incorporation of [U-14C] Glucose into Lipids in Rat Aorta

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Abstract
In vitro aortic lipogenesis from D-[U-14C]glucose was significantly greater in meal-fed rats than in ad libitum fed controls. In addition, aortic tissue from meal-fed rats showed a sensitivity to insulin which was absent in the same preparations from nibbling rats. Two preparations of aortic tissue were used in this study. “Intima-media” contained intima and approximately the inner two-third of the media. “Adventitia” contained the remainder of the media and the inner, fat-free adventitia. This latter preparation was more sensitive to the change from a nibbling to a meal-eating regime, although the effects were clearly evident in the intimamedia, suggesting that both adventitial and medial cells were susceptible to the metabolic changes associated with the adaptation to meal-eating. Of the two major aortic lipid components synthesized from glucose in vitro, phospholipids and triglycerides, the former were essentially unaltered in meal fed rats. However, in comparison with nibbling rats, 14C-incorporation into aortic triglycerides was increased two-fold in the intima-media and three-fold in the media-adventitia, and was almost doubled again in both preparations in the presence of insulin. The development of adaptive hyperlipogenesis and insulin sensitivity in these preparations is discussed in terms of possible variations in insulin receptor number in target tissues of mealfed rats.