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.

Comparative effects of several simple carbohydrates on erythrocyte insulin receptors in obese subjects

The effects of simple carbohydrates on erythrocyte insulin receptors, plasma insulin and plasma glucose were studied during four hypocaloric, hyperproteic, diets. One diet contained no carbohydrate; the other three contained 36 g of either glucose, galactose or fructose. These diets were given for a 14-day period to groups of moderately obese subjects. The hypocaloric carbohydrate-free diet produced a decrease in plasma insulin and glucose concentrations concomitant with an increase in the number of insulin receptors. A similar increase in insulin receptor number was found when the diet was supplemented with glucose or galactose, but not with fructose. The presence of fructose in the diet prevented any increase in insulin receptor number.

Effects of metformin treatment on erythrocyte insulin binding in normal weight subjects, in obese non diabetic subjects, in type 1 and type 2 diabetic patients

We have evaluated the effects of metformin administration on erythrocyte insulin receptors in 21 subjects: 5 normal weight subjects, 5 obese non diabetics, 5 insulin-dependent diabetics (Type I) and 6 obese non insulin-dependent (Type II) diabetics. Plasma glucose, plasma insulin and erythrocyte insulin receptors were studied after 15 days of metformin (850 mg, t.d.) or placebo administered in a double blind random order. Maximum specific insulin binding to erythrocytes increased after metformin in the normals (p less than 0.01), in the obese non diabetics (p less than 0.01) and in the obese Type 2 diabetics (p less than 0.005), but not in Type I diabetics. Scatchard analysis showed that the receptor number per cell increased by 37% in the normals, by 17% in the obese non diabetics and by 182% in Type 2 diabetics. Receptor affinity increased in obese subjects but did not increase in normals and in diabetics. Only in Type II diabetics was there a significant decrease in plasma glucose. Metformin, thus, increased binding in normals by moderately increasing the capacity of cell receptors, in obese non diabetics by increasing the affinity, whereas in obese Type II diabetics it dramatically increases receptor capacity. This is consistent with the fact that metformin has a hypoglycaemic effect mainly in Type II diabetics, but not in non diabetics (whether obese or not), and could be due to a direct effect on the cell membrane.

Insulin receptor changes in type 2 diabetes after short term insulin treatment

We have studied erythrocyte insulin receptor changes before and after 8 days of continuous subcutaneous insulin infusion by a pump in 11 uncontrolled obese non-insulin-dependent diabetics (type 2), diet and drug resistant for at least three months previously. All the patients were hospitalized. On day 1 of the study, their oral hypoglycemic agents were stopped and hypocaloric diet (1000 Kcal/day) was maintained (strictly reinforced). This period of reinforced treatment was not accompanied by correction of hyperglycemia. On day 9 patients were placed for 12 hours on artificial pancreas in order to bring their fasting blood glucose levels down to normal values. Then they were submitted to a continuous subcutaneous insulin infusion (CSII) for the following 8 days. There was a significant decrease in mean fasting plasma glucose (P less than 0.001) and a rise in insulin (P less than 0.05) levels after insulin treatment. Mean specific insulin binding was also significantly increased (P less than 0.01). The increase in binding (with insulin therapy) correlated with the fall in fasting hyperglycemia (r = 0.786, P less than 0.01). In addition, the increase in binding correlated negatively with changes in fasting plasma insulin levels (r = -0.867, P less than 0.01), under treatment, on one hand and with the dose of exogenous insulin administered (r = -0.681, P less than 0.05) on the other hand. There was no correlation between binding and fasting plasma insulin levels (before and after insulin therapy), or between diabetes duration and any of the previous parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate intake affects insulin binding to human erythrocytes in normal weight subjects but not in subjects with family obesity

The effects of different carbohydrate intakes on insulin binding to human erythrocytes were studied in thirty nine obese and twelve normal weight subjects belonging to twelve families with a strong penetrance of obesity("family experiment"), and in nine normal weight subjects with no family or personal history of obesity or diabetes ("diet experiment"). In the "family experiment," the mean insulin binding in obese subjects was significantly lower than in control normal weight siblings and parents. This difference cannot be related to an increase in carbohydrate or caloric intakes, since there was no difference in daily food intake between the obese and the control subjects. In the "diet experiment," the volunteers were studied four times: twice with their spontaneous diet, one with a normocaloric carbohydrate rich diet and once with a normocaloric fat rich diet. Both the carbohydrate and fat rich diets resulted in a significant lowering of binding when compared to the period of spontaneous diet. In the two experiments, the decrease in binding is due to a decrease in the number of receptors per erythrocyte. The possibility of a common underlying mechanism is discussed.