Insulin-like growth factor I (IGF-I) and insulin binding to erythrocytes of normal prepubertal children and adults.
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)
Dooghe
C
C
Laboratoire de Physiologie, Biologie de la Reproduction et du Développement, Clermont-Ferrand I, France.
Grizard
G
G
Labbe
A
A
Dardevet
D
D
Meyer
M
M
Grizard
J
J
D000328:Adult; D002648:Child; D002675:Child, Preschool; D004912:Erythrocytes / Q000378:metabolism* / Q000648:ultrastructure; D005260:Female; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007456:Iodine Isotopes; D008297:Male; D008875:Middle Aged; D011485:Protein Binding; D011627:Puberty / Q000378:metabolism*; D011972:Receptor, Insulin / Q000378:metabolism
D007328:Insulin; D007456:Iodine Isotopes; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin