Baxter R C, Zaltsman Z, Turtle J R
J Clin Endocrinol Metab. 1984 Jun;58(6):955-9. doi: 10.1210/jcem-58-6-955.
Milk contains cell growth factors, but somatomedin-C/insulin-like growth factor I has not previously been identified. Acid-ethanol extracts of fresh human milk samples displaced somatomedin-C tracer from the specific somatomedin-C antiserum Tr4 parallel to standard. In samples obtained between days 1 and 9 postpartum, highest levels [17.6 +/- 10.4 (+/- SD) ng/ml; n = 7) were found in day 1 samples; these fell to stable levels of 6-8 ng/ml over the next several days. Sephadex G-200 chromatography of fresh 1- to 2-day-postpartum milk samples revealed immunoreactive peaks of approximately 150,000 and 40,000 mol wt, accounting for about 80% of the immunoreactivity; the remainder corresponded in elution volume to free somatomedin-C. On chromatography of the high molecular weight fractions in 1 M acetic acid, most of the immunoreactivity shifted to the position of somatomedin-C. Milk samples stripped of their endogenous somatomedins by ion exchange chromatography at low pH specifically bound somatomedin-C tracer in proportion to the amount of added protein up to 20% binding. Displacement of tracer by unlabeled somatomedin-C indicated an association constant of about 1 X 10(10) liter/mol. Fresh milk incubated with somatomedin-C tracer and fractionated by neutral gel chromatography bound the tracer predominantly in the 40,000 mol wt region, which was abolished when excess unlabeled peptide was included in the incubation. These results indicate that fresh human milk contains immunoreactive somatomedin-C, of which a significant proportion is not protein bound at neutral pH. Somatomedin-C may account for some of the mitogenic activity of milk reported by others. The role of this activity in neonatal growth is unknown.
牛奶含有细胞生长因子，但此前尚未鉴定出生长调节素-C/胰岛素样生长因子I。新鲜人乳样品的酸乙醇提取物可使特异性生长调节素-C抗血清Tr4中的生长调节素-C示踪剂与标准品平行移位。在产后第1天至第9天采集的样本中，第1天的样本中生长调节素-C水平最高[17.6±10.4（±标准差）ng/ml；n = 7]；在接下来的几天里，这些水平降至6 - 8 ng/ml的稳定水平。对产后1至2天的新鲜母乳样品进行葡聚糖G - 200色谱分析，发现免疫反应峰的分子量约为150,000和40,000道尔顿，约占免疫反应性的80%；其余部分在洗脱体积上与游离生长调节素-C相对应。对高分子量组分在1 M乙酸中进行色谱分析时，大部分免疫反应性转移到了生长调节素-C的位置。通过在低pH下进行离子交换色谱去除内源性生长调节素的母乳样品，可按添加蛋白量的比例特异性结合生长调节素-C示踪剂，结合率高达20%。未标记的生长调节素-C对示踪剂的置换表明其缔合常数约为1×10¹⁰升/摩尔。用生长调节素-C示踪剂孵育新鲜牛奶并通过中性凝胶色谱进行分离，示踪剂主要结合在分子量40,000道尔顿的区域，当孵育中加入过量未标记肽时，这种结合被消除。这些结果表明，新鲜人乳中含有免疫反应性生长调节素-C，其中很大一部分在中性pH下不与蛋白质结合。生长调节素-C可能是其他人报道的牛奶促有丝分裂活性的部分原因。这种活性在新生儿生长中的作用尚不清楚。
