Effects of cell size and exercise on glucose uptake and metabolism in adipocytes of female rats

The purpose of this study was to attain a better understanding of how the adipocyte transports and metabolizes glucose with and without the influence of exercise training. Rates of 2-deoxyglucose and glucose oxidation, using [1-14C]-and [6-14C]glucose, were measured in adipocytes from exercise-trained and sedentary control female rats of the same age. The trained animals were exercised by swimming, 6 h/day, 5 days/wk for 10 wk. The fat cells of the sedentary rats were significantly larger (P less than 0.005) than the trained animals and had very low rates of glucose uptake and [1-14C]- and [6-14C]glucose oxidation. The adipocytes of the trained rats were very responsive to insulin with 2-deoxyglucose rates seven times higher than those of the control animals and [1-14C]- and [6-14C]-glucose oxidation rates 14- and 13-fold (respectively) larger than control values. Comparisons of the data from exercised animals to younger sedentary rats indicates that glucose oxidation remains normal in the adipocytes of the trained animals whereas glucose transport is greatly improved. If the older sedentary controls are compared to younger animals, it can be seen that as the cell enlarges it loses its ability to take up or metabolize glucose. The combination of a loss in glucose transporting capacity with cellular enlargement and an increase in glucose uptake with exercise training suggests that movement of glucose across the cell membrane may be a limiting factor in glucose utilization in fat cells.