Data emerging from insulin receptor studies performed on red blood cells (RBCs) and monocytes from the same subject are not always in agreement; dichotomy might occur since variations in mean RBC age are not taken into account or because insulin receptors on the two cell types behave differently.

In the present investigation RBCs from normal male subjects were separated into five populations of different mean age by means of centrifugation of RBCs on a discontinuous gradient of buffered Percoli for 10 min at 1000 x g. Insulin binding varied significantly depending upon the RBC population tested and was closely correlated to the activity of pyruvate kinase (r2 = 0.86), a well-known marker of RBC age.

These data suggested that pyruvate kinase assay might be helpful in studies of RBCs. To confirm this hypothesis, RBCs from 10 normal male subjects and 13 male patients with hemolytic anemia were studied; insulin binding was correlated to pyruvate kinase activity. By adjusting insulin binding to 2 x 109 RBCs/ml the range of data was abnormally high, but it became acceptable after adjusting insulin binding to pyruvate kinase activity (0.75 U/2 x 109 RBCs). The overalr2 = 0.82) but only slightly to reticulocyte number (r2 = 0.56) since not only reticulocytes but also erythrocytes lose receptors during maturation.

Pyruvate kinase activity was measured in RBCs from normal men and from normally menstruating women at the seventh and twenty-fourth days of the cycle; results demonstrated that adjustment of data, according to mean RBC age, broadens dichotomy of monocyte and RBC data.

In conclusion, this paper demonstrates that (1) insulin binding experiments may be carried out on RBCs separated into populations of different mean age; (2) by assaying the pyruvate kinase activity, it is possible to study RBC samples of different mean age and to reveal insulin binding variations provoked by changes in mean RBC age; (3) RBCs lose insulin receptors physiologically and continuously with age; (4) RBC insulin receptors of patients with hemolytic anemia are normal; and (5) monocyte and RBC insulin receptors may behave differently.

This content is only available via PDF.