Comparative effects of 6 week fructose, dextrose and starch feeding on fat-cell lipolysis in normal rats: effects of isoproterenol, theophylline and insulin.

The precise effects of fructose feeding on adipose tissue is not clearly known. Consequently, we studied the effects of fructose feeding on stimulated and inhibited in vitro lipolysis. Twenty seven male Sprague Dawley rats, 5 weeks of age, were fed for 6 weeks on one of three diets containing 57% CHO as fructose (F), dextrose (D) or starch (S). At week 6 the epididymal fat pad weights showed no difference between groups. Stimulation of lipolysis by isoproterenol or theophylline showed: decreased sensitivity of adipocytes to isoproterenol, but not to theophylline, in F (p less than 0.05); the maximal responses were decreased, but NS, after stimulation by either isoproterenol or theophylline. The maximal antilipolytic responses to insulin were increased in F (27%) and D (29%) when compared to S (16%), (p less than 0.05). Only, in F there was an increase (NS) in ED50 (0.63 +/- 0.23 ng/ml) compared to D (0.45 +/- 0.18) and S (0.29 +/- 0.18), indicating decreased sensitivity. Nonfasting plasma insulin and triglycerides were increased at the 6th week in F (p less than 0.01), without any change in plasma glucose levels. However, there was no difference in 12 h fasting plasma glucose, insulin or triglycerides. In conclusion, a 6 week 57% fructose containing diet in normal rats led to: 1) decreased lipid mobilization in the epididymal adipose tissue; and 2) increased nonfasting plasma insulin and triglycerides. Thus fructose, under these experimental conditions, seems to have adverse metabolic effects in normal rats.