Acute Reversal of the Enhanced Insulin Action in Trained Athletes: Association with Insulin Receptor Changes

We studied the effect of aerobic training and detraining on insulin-stimulated glucose disposal and on erythrocyte insulin receptor binding. Seven endurancetrained athletes were studied at 12 h, 60 h, and 7 days after cessation of training and compared with three untrained, age- and weight-matched controls. The metabolic clearance rate of glucose as measured by the euglycemic clamp technique was 15.6 ± 1 . 8 ml/kg/min (mean ± SEM) in the trained subjects 12 h after the last bout of exercise compared with 7.8 ± 1.2 ml/kg/min in the untrained control group. When the trained subjects refrained from physical training, the metabolic clearance rate decreased to 10.1 ± 1 . 0 ml/kg/min at 60 h and further to 8.5 ± 0.5 ml/kg/min after 7 days of detraining. The percentage of specific insulin binding to young erythrocytes (density 1.089–1.092), isolated by density gradient centrifugation, decreased from 10.4 ± 0.9 at 12 h after the last exercise to 8.1 ± 0.7%/3 × 109 cells after 60 h of detraining (P < 0.001). The decrease in insulin binding to erythrocytes was almost entirely accounted for by a decrease in the number of insulin receptors. We conclude that the increase in peripheral insulin action seen in trained athletes is rapidly reversed, possibly by a mechanism separate from other phenomena associated with chronic training. The parallel findings of decreased in vivo insulin action and decreased insulin binding in young erythrocytes suggest that modulation of in vivo insulin response by detraining may be at least partially mediated by changes in insulin receptor number. Isolated young erythrocytes are better indicators of acute insulin receptor modulation than are whole cell preparations.