Erythrocyte insulin-like growth factor-I receptor evaluation in normal subjects, acromegalics, and growth hormone-deficient and insulin-dependent diabetic children

Insulin-like growth factor-I (IGF-I) receptors are characterized in several animal and human tissues. IGF-I receptor studies performed in erythrocytes to assess IGF-I receptor status at target-cell tissues are potentially useful for clinical studies, since tissue biopsies or cultures are not required. However, validation of results is challenged by some investigators on the basis of discrepancies described in comparative studies with other cell types, probably related to populations of different cell ages affecting binding to red blood cells (RBCs). By correcting cell age for creatine, we studied IGF-I receptor status in 24 normal subjects (11 adults and 13 children, eight prepubertal and five pubertal) and 33 patients with pathologic conditions (five adult acromegalics, six children with pituitary dwarfism, and 22 type I diabetic children, 15 prepubertal and seven pubertal). Acromegalic patients with higher plasma IGF-I and insulin levels presented lower IGF-I specific binding ([B o] mean ± SEM, 6.1% ± 0.8%) and affinity ([ED 50] 28.5 ± 2.2 ng/mL) than normal adults (B o, 10.9% ± 0.7%; ED 50, 16.4 ± 0.9 ng/mL; P < .001), and growth hormone (GH)-deficient children showed higher IGF-I binding (24.6% ± 1.7%, P < .001) without significant affinity alterations than normal prepubertal children (B o, 14.7% ± 1.0%). Both prepubertal and pubertal type I diabetic children with higher GH levels presented decreased IGF-I binding (11.4% ± 0.9% for prepubertal, P < .05; 10.0% ± 1.1% for pubertal, P < .05) to RBC receptors in comparison to the respective control group (14.7% ± 10% and 14.9% ± 1.3%, prepubertal and pubertal, respectively). Whereas in pubertal diabetics mean IGF-I basal levels were significantly reduced as compared with the respective controls, no difference was observed in mean IGF-I basal levels in normal and diabetic prepubertal children.