Rao R K, Philipps A F, Williams C S, McCracken D M, Koldovsky O
Department of Pediatrics, University of Arizona College of Medicine, Tucson, USA.
J Pediatr Gastroenterol Nutr. 1998 Feb;26(2):179-85. doi: 10.1097/00005176-199802000-00012.
Insulin-like growth factors (IGF)-I and -II are present in milk of a number of mammalian species. The stability of IGF-I and -II in the intestinal lumen was investigated by measuring the proteolytic degradation of 125I-labeled IGF-I and IGF-II by rat (suckling and adult) intestinal luminal flushings in vitro.
Degradation of 125I-labeled IGF-I and IGF-II was assessed by measuring the generation of acid-soluble radioactivity and the reduction of the amounts of peak activity (gel filtration). Degradation was confirmed by measuring the loss of immunoreactivity and receptor activity.
Incubation of 125I-IGF-I with midjejunal luminal flushings from 12-day-old suckling rats generated acid-soluble radioactivity in a time- and dose-(flushing) dependent manner, whereas incubation of 125I-IGF-II produced only minor amounts of acid-soluble radioactivity. Degradation activity in luminal flushings from adult rat intestine was several times greater than that in luminal flushings from suckling rats. Degradation of 125I-IGF-II was several times lower than that of 125I-IGF-I in the intestinal luminal flushings from suckling and adult rats. The rate of decrease in immunoprecipitable 125I-IGF-I was considerably lower than the rate of decrease in receptor-active radioactivity. Except for immunoreactivity, analyses of acid-precipitable, peak-A, and receptor-active radioactivities demonstrate that IGF-II is relatively more stable than IGF-I in luminal flushings of suckling rat duodenum, jejunum, and midjejunum.
These results show that the stability of IGF in the gastrointestinal lumen depends on the age of the animal and the segment of the gastrointestinal tract, as well as on the peptide isoform.
胰岛素样生长因子（IGF）-I和-II存在于多种哺乳动物的乳汁中。通过在体外测量大鼠（哺乳和成年）肠腔冲洗液对125I标记的IGF-I和IGF-II的蛋白水解降解，研究了IGF-I和IGF-II在肠腔中的稳定性。
通过测量酸溶性放射性的产生和峰值活性（凝胶过滤）量的减少来评估125I标记的IGF-I和IGF-II的降解。通过测量免疫反应性和受体活性的丧失来确认降解。
125I-IGF-I与12日龄哺乳大鼠空肠中段冲洗液孵育，以时间和剂量（冲洗液）依赖性方式产生酸溶性放射性，而125I-IGF-II孵育仅产生少量酸溶性放射性。成年大鼠肠腔冲洗液中的降解活性比哺乳大鼠肠腔冲洗液中的降解活性高几倍。在哺乳和成年大鼠的肠腔冲洗液中，125I-IGF-II的降解比125I-IGF-I低几倍。可免疫沉淀的125I-IGF-I的减少速率明显低于受体活性放射性的减少速率。除免疫反应性外，对酸沉淀、峰A和受体活性放射性的分析表明，在哺乳大鼠十二指肠、空肠和空肠中段的冲洗液中，IGF-II比IGF-I相对更稳定。
这些结果表明，IGF在胃肠道腔中的稳定性取决于动物的年龄、胃肠道的节段以及肽异构体。
