Morris A H, Joyce J L, Reiter E O
Baystate Medical Center, Department of Pediatrics, Springfield, Massachusetts 01199.
Pediatr Res. 1989 Apr;25(4):409-13. doi: 10.1203/00006450-198904000-00021.
Young children are growing at a time when circulating levels of IGF-I measured by RIA are generally less than or equal to values in nongrowing adults. 125I-Thr59-IGF-I binding to receptors on conveniently available red blood cells was studied in 33 normal adults (nine males, 24 females) and 13 normal prepubertal children aged 3-10 y (10 boys, three girls; all Tanner stage 1). Red blood cell specific binding of 125I-Thr59-IGF-I was determined by displacement of labeled Thr59-IGF-I by unlabeled Thr59-IGF-I or insulin in a dose-dependent manner. Mean (+/- SEM) 125I-Thr59-IGF-I specific binding was significantly higher (p = 0.01) in prepubertal children than in adults (13.9 +/- 0.7% versus 11.6 +/- 0.5%/3 x 10(9) cells/mL). Specific binding did not differ between adult males and females. There was no significant correlation between specific binding and reticulocyte count. Scatchard analysis demonstrated a linear plot. Increased binding to red blood cells in the prepubertal children appeared to be due to an increase in receptor affinity (Ka = 4.97 +/- 0.42 x 10(8) M-1 versus 3.70 +/- 0.41 x 10(8) M-1; children versus adults; p = 0.03). Mean receptor concentrations were not different in children and adults (64.4 +/- 8.5 versus 58.0 +/- 5.6 binding sites/cell). There was a significant positive correlation between 125I-Thr59-IGF-I specific binding and affinity (p = 0.007, r = 0.39). We speculate that the greater specific binding of labeled Thr59-IGF-I to red blood cells in prepubertal children may provide a mechanism for enhanced cellular responsiveness to relatively low levels of circulating IGF-I.
幼儿成长时期，通过放射免疫分析法测定的循环中IGF-I水平通常低于或等于非成长成年人的水平。在33名正常成年人（9名男性，24名女性）和13名3至10岁的正常青春期前儿童（10名男孩，3名女孩；均为坦纳1期）中，研究了125I-Thr59-IGF-I与方便获取的红细胞上受体的结合情况。125I-Thr59-IGF-I的红细胞特异性结合通过未标记的Thr59-IGF-I或胰岛素以剂量依赖性方式取代标记的Thr59-IGF-I来确定。青春期前儿童中125I-Thr59-IGF-I的平均（±SEM）特异性结合显著高于成年人（13.9±0.7%对11.6±0.5%/3×10⁹细胞/mL；p = 0.01）。成年男性和女性之间的特异性结合没有差异。特异性结合与网织红细胞计数之间没有显著相关性。Scatchard分析显示为线性图。青春期前儿童红细胞结合增加似乎是由于受体亲和力增加（Ka = 4.97±0.42×10⁸ M⁻¹对3.70±0.41×10⁸ M⁻¹；儿童对成年人；p = 0.03）。儿童和成年人的平均受体浓度没有差异（64.4±8.5对58.0±5.6个结合位点/细胞）。125I-Thr59-IGF-I特异性结合与亲和力之间存在显著正相关（p = 0.007，r = 0.39）。我们推测，青春期前儿童中标记的Thr59-IGF-I与红细胞的更大特异性结合可能为增强细胞对相对低水平循环IGF-I的反应性提供一种机制。
