Diurnal variation in specific insulin binding to erythrocytes

We studied the insulin binding to erythrocytes during a 24-h period in 11 normal subjects. Compared with 0800 and 1600 h the specific 125I-insulin binding decreased significantly at midnight. These changes were mainly due to alterations in insulin binding affinity rather than a decrease in receptor number. An inverse finding was obtained concerning the plasma insulin levels. In fact, the highest insulin concentrations were observed at midnight. The results suggest that diurnal variations in insulin receptor function occur in response to fluctuations of plasma insulin levels.