Decreased insulin binding to adipocytes precedes both hyperinsulinemia and decreased insulin binding to erythrocytes in cafeteria-fed rats

The relationship between food intake, obesity, insulin binding to adipocytes and erythrocytes, plasma insulin and plasma glucose was studied in an animal model of nutritional obesity--'the cafeteria-fed rats'--after 3 days, 10 days, and 3 weeks of cafeteria feeding. The antilipolytic effect of insulin was also studied. The cafeteria-fed rats ate more carbohydrates after 3 days of diet, while from the 10th day, as previously found, they ate about the same amount of carbohydrates but more lipids and increased in weight. Insulin binding to adipocytes started to decrease (P less than 0.05) 10 days after beginning the cafeteria diet despite the absence of hyperinsulinemia. This decrease in insulin binding to adipocytes was accompanied by a decrease in the responsiveness of adipocytes to the antilipolytic effect of insulin. Hyperinsulinemia (P less than 0.01) appeared only after 3 weeks. At the same time, insulin binding to erythrocytes started also to decrease (P less than 0.05). Plasma glucose levels in the cafeteria-fed rats were unchanged when compared to their controls at any time of the study. There was no correlation between body weight, plasma insulin and insulin binding, to adipocytes and to erythrocytes, at any time of the study. Thus it is possible that factors other than hyperinsulinemia could be involved in the decrease in insulin binding to both adipocytes and erythrocytes.