Studies on the metabolic effects induced in the rat by a high-fat diet. (U- 14 C) glucose metabolism in epididymal adipose tissue.

Abstract

Rats were fed for 3–4 weeks from weaning either a control carbohydrate diet (58% starch) or one of two fat diets (35.5% and 58% lard); some rats were changed from fat (35.5%) to control diet 1 to 5 days before the experiment. Epididymal adipose tissue was incubated in the presence of [U-14C]glucose (10 mM) and (or no) insulin (100 μU/ml). Glucose uptake and conversion into CO2, glycogen, fatty acid and glyceride-glycerol were measured together with lactate and glycerol release during a 2-hour incubation. The level of free fatty acids in tissue was also determined. Incorporations of glucose carbon into CO2 and fatty acid were severely reduced by both fat diets and increased during the first 5 days after change to control diet in an almost linear way, to values still far from the control values. After both fat diets, lactate release was doubled, accounting for half the glucose uptake. Lipolysis, measured by glycerol release, was unchanged (35.5% fat) or increased (58% fat) by fat diet, but the antilipolytic effect of insulin was entirely preserved in both fat conditions. A 6-hour preincubation of the tissue with glucose increased glucose uptake and metabolism in adipose tissue of control and fat-fed rats, independently of the presence of insulin (50 μU/ml) in the medium. This effect does not seen to have any relation with the progressive restoration of lipogenesis observed after changing the animals from fat to carbohydrate diet.