Minimal hydrolysis of epidermal growth factor by gastric fluid of preterm infants.
Minimal hydrolysis of epidermal growth factor by gastric fluid of preterm infants.
复制标题
早产儿胃液对表皮生长因子的最小水解。
作者：
Britton,JR;George-Nascimento,C;Udall,JN;Koldovský,O
乳中存在高浓度的表皮生长因子（EGF），可能在胃肠道的生长中起作用。如果摄取的EGF要在胃肠道内发挥作用，胃部对蛋白质水解降解的抵抗力是必要的。虽然EGF对低pH值和蛋白酶的稳定性预示着胃的存活，但胃的消化程度仍有待确定。因此，我们采用体外方法测量了125i -人重组EGF在早产儿胃中的降解情况，其中EGF在37℃下与pH为1.8、3.2和5.8的胃液孵育，然后分析降解产物。由于早产婴儿在喂养后1小时出现最大的酸蛋白水解活性，因此从18名出生时平均胎龄为30.4（3.0）周、出生后平均胎龄为26.3（12.7）天的婴儿中采集了当时的液体。与在相同条件下发生的碘化酪蛋白的大量水解相比，孵育长达60分钟显示三氯乙酸可沉淀放射性的最小损失。在Sephadex G-25上对反应混合物进行色谱分析，发现与EGF共溶的单一主放射性峰。与胃液孵育后，表皮生长因子与抗egf亲和柱和胎盘膜受体结合的能力也保持了75%以上。这些数据支持了摄取的EGF在早产儿中具有潜在生物活性形式的大量胃存活的概念。
Epidermal growth factor (EGF), present in high concentrations in milk, may play a role in growth of the gastrointestinal tract. Resistance to proteolytic degradation in the stomach is necessary if ingested EGF is to function within the gastrointestinal tract. Although EGF stability to low pH and proteases predicts gastric survival, the extent of digestion in the stomach remains to be defined. Consequently, we measured gastric degradation of 125I-human recombinant EGF in preterm infants with an in vitro method in which EGF was incubated at 37 degrees C with stomach fluid at pH 1.8, 3.2, and 5.8 followed by analysis of degradation products. As maximal acid proteolytic activity is present one hour after feeding in preterm infants, fluid was obtained at that time from 18 infants with a mean gestational age at birth of 30.4 (3.0) (SD) weeks and a postnatal age of 26.3 (12.7) days at sampling. Incubations for up to 60 minutes revealed minimal loss of trichloroacetic acid precipitable radioactivity, in contrast to the substantial hydrolysis of iodinated casein which occurred under the same conditions. Chromatography of reaction mixtures on Sephadex G-25 showed a single major peak of radioactivity which coeluted with EGF. Epidermal growth factor also retained greater than 75% of its ability to bind to anti-EGF affinity columns and placental membrane receptors after incubation with gastric fluid. These data support the concept of substantial gastric survival of ingested EGF in a potentially biologically active form in preterm infants.