Insulin-Like Growth Factor I (IGF-I) and Insulin Binding to Erythrocytes of Normal Prepubertal Children and Adults

Abstract

Erythrocyte insulin-like growth factor I (IGF-I) and insulin receptors were characterized in 10 normal prepubertal children (5 girls and 5 boys) aged 4-11 yrs and 10 normal adults (4 women and 6 men) aged 32-47 yrs. erythrocytes were purified from 5 ml of blood by Ficoll-Paque gradient centrifugation. Reticulocytes count in the erythrocyte suspensions were lower than 1%. Insulin and IGF-I binding assays were performed simultaneously. Maximal percent binding of [125I] labelled IGF-I was significantly higher in prepubertal children than in adults (8.7 +/- 0.7% versus 6.2 +/- 0.5% at a concentration of 5 x 10(9) erythrocytes/ml). Scatchard analysis revealed the high affinity constant was better in prepubertal children (Ka = 4.6 +/- 1.3 nM-1 versus 1.8 +/- 0.2 nM-1), whereas the binding capacity was similar (5.8 +/- 1.1 versus 7.7 +/- 0.8 high affinity binding sites/cell). In both groups, unlabelled IGF-I inhibited tracer-binding half maximally at about 1 nM. Insulin was 100-fold less potent. In adults, specific binding of [125I] labelled IGF-I was higher in women (7.6 +/- 0.7%) than in men (5.3 +/- 0.4%). No significant difference was observed in maximal specific binding of [125I] labelled insulin between prepubertal children (8.2 +/- 0.5%) and adults (7.2 +/- 0.7%). In both groups, competition by unlabelled insulin for [125I] labelled insulin binding gave 50% displacement for approximately 0.25 nM and IGF-I was about 80-fold less potent. Both IGF-I and insulin binding parameters were not significantly correlated with plasma hormone levels. In prepubertal children, the high-affinity IGF-I receptors number decreased with increasing high-affinity insulin receptors number.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased number of IGF‐I receptors on erythrocytes of women with polycystic ovarian syndrome

“…The results of this study demonstrate that women with PCOS have an increased number of IGF-I receptors on erythrocytes in comparison to normo-ovulatory women. Although the mature erythrocyte has no nucleus it reflects the intrinsic genetic programming of the primary cell and previous insulin and IGF-I binding studies have shown that it is an acceptable tissue for evaluating changes in receptor concentration and affinity (Geffner et al, 1987;Ward, 1988;Dooghe et al, 1991;Eshet et al, 1993). Unlike previous studies, demonstrating that IGF-I regulates its own receptor on erythrocytes (Eshet et al, 1991(Eshet et al, , 1993Hochberg et al, 1992), we found no difference in serum IGF-I levels between PCOS and controls, both being within the normal range.…”

Modulation of IGF‐I receptors by exogenous hGH treatment in constitutionally short children

“…It has since been clearly demonstrated not only that erythroid progenitor cells respond to stimulation by IGF-I, indicating the presence of IGF-I receptors (Geffner et al, 1987), but also that erythrocytes (RBC) originating from these cells have specific IGF-I receptors (Polychronakos et al, 1983). Because it is easy to obtain a large number of RBC from small volumes of blood, they are now being used in clinical investigations (Hizuka et a!., 1985;Catanese et al, 1986;Izumi et a!., 1986;Dooghe et al, 1991). Eshet et al (1991;1993) recently demonstrated that there is an increase in IGF-I binding sites on RBC and increase in mRNA of IGF-I receptor in lymphocytes of patients with chronic low IGF-I serum concentrations.…”