Bidirectional alteration of insulin receptor affinity by different forms of physical exercise

Insulin binding of monocytes and erythrocytes was studied in untrained male volunteers after 15 min of exhaustive bicycle exercise (EE) and several days later after moderate exercise (ME) for 90 min. Insulin receptor affinity decreased after EE in monocytes (26.4% decrease; P less than 0.01) and in erythrocytes (10.4%; P less than 0.05) with no change in receptor number. After ME, however, binding to monocytes was enhanced by 15.2% (P less than 0.05) due to increased receptor affinity. The number of circulating monocytes was markedly increased after both forms of exercise, averaging 105% after EE and 57% after ME. The bidirectional effect on monocyte insulin binding could be reproduced in vitro by incubation of preexercise cells with post-exercise serum: 12.4% (P less than 0.05) decrease with EE serum and 6.1% (P less than 0.05) increase with ME serum. The effect was prevented by overnight dialysis. These results suggest that physical exercise not only entails adjustment of serum insulin but also of cellular hormone sensitivity, presumably through the mediation of low-molecular-weight serum components.