Red blood cell age, pyruvate kinase activity, and insulin receptors. Evidence that monocytes and RBCs may behave differently

Ontogenesis of insulin receptors in human cerebral cortex

This study examines the ontogenesis of insulin receptors in human cerebral cortex. Synaptosomal membrane fraction was obtained after subcellular fractionation of human brain tissue. The 24 cases studied were classified according to the statistical differences found in: Group I, pre-term, up to 30 weeks of gestation; group II, full-term and newborns; group III from one year to adulthood. Scatchard plots of insulin binding to brain membranes were curvilinear and showed a decrease in insulin receptor number as a function of age with slight differences in affinity. Receptor number were 3.0 +/- 0.8 pmol/mg in Group I, 0.6 +/- 0.14 pmol/mg and 0.2 +/- 0.024 pmol/mg in Groups II and III respectively. Values of 5'nucleotidase and Na+ K+ ATPase activities, were similar in all groups, which indicates that the purity of the fraction used for binding was similar in each group. According to the ontogenic profile in insulin binding described in this work, it may be assumed that the higher concentration of insulin receptors in human brain during the fetal period can determine some insulin action in this early stage of maturation, even though the functionality of these receptors remains to be elucidated.

Erythrocyte insulin receptor: normalization of binding data for the average cell age by the red cell creatine determination in obese, diabetic and acromegalic patients

Insulin binding studies performed in erythrocytes (RBC) have been employed in clinical studies assessing the status of insulin receptors at target cell tissues. However, some authors challenged this assumption on the basis of some discrepancies described in comparative studies of other cell types, probably related to populations of different cell age affecting insulin binding to RBC. We evaluated insulin binding to RBC in normal males (n = 10), non-obese diabetic males (n = 13), normal females (n = 15), obese (n = 11) and acromegalic females (n = 5), before and after correction of insulin binding data for creatine concentration in the RBC as a procedure of correction for age, since a negative correlation was described between creatine content and RBC age which also correlates inversely with % insulin binding. Insulin binding in all three groups of patients was not statistically different from corresponding values for normal males and females respectively before correction of data for creatine, but significantly reduced values were found after adjustment for creatine in accordance with published data concerning monocytes. In conclusions, the procedure of correcting insulin binding in erythrocytes by the creatine content in RBC is potentially useful for clinical investigations, since the influence of RBC age is excluded.

Characterization of differences in insulin receptors from young and old red blood cells

It has been demonstrated that young RBCs (reticulocytes and early mature erythrocytes) possess more insulin receptors than old RBCs (late mature erythrocytes) but it is not yet known whether insulin receptors on young and old RBCs are regulated similarly. In the present investigation insulin receptors on young and old RBCs have, therefore, been studied in five normal male subjects before and after 2 days dexamethasone ingestion (0.5 mg tablet every 6 h) and, in the same subjects, before and 5 h after ingestion of 75 g glucose. The results obtained clearly demonstrate that dexamethasone increases insulin receptor concentration while glucose ingestion increases both insulin receptor affinity and concentration on young RBCs. By contrast, neither stimuli modify insulin receptors on old RBCs. Studies on RBCs are usually performed on the whole RBC population not taking into account this differential responsiveness of receptors on young versus old RBCs; consequently, this phenomenon might be responsible of the fact that some data reported on RBCs are not in agreement with those reported on monocytes or adipocytes and it should be taken into consideration when using RBCs to evaluate insulin receptor regulation.