Watts C, Gain K R
Diabetes. 1984 Jan;33(1):50-6. doi: 10.2337/diab.33.1.50.
The apparent hyperinsulinemia seen in the fetal rat in late gestation (day 20) is shown to be due to an immunoreactive insulin (IRI) species peculiar to the fetal rat, and not monomeric insulin. This species disappears within 12 h after birth and only insulin as found in the adult can then be detected. The fetal serum IRI has a molecular weight of approximately 11,000 and differs from monomeric insulin and proinsulin in its behavior on gel filtration and anion-exchange chromatography. The activity of fetal serum in an insulin bioassay based on the incorporation of glucose into lipid was half that expected on the basis of the serum IRI concentration. The addition of fetal serum to purified insulin or proinsulin caused an increase in the apparent molecular weight of both hormones by 2000. In the case of insulin, the generated species of mol wt 8000 was clearly differentiated from the endogenous species (11,000) on Sephadex G50. The fetal pancreas at this age was found to contain predominantly monomeric insulin that had full biologic activity in the insulin bioassay. It is postulated that the fetal pancreas secretes monomeric insulin, which is then modified in the circulation to a complex with reduced biologic activity. This process appears to have two steps in that in vitro fetal serum increases the apparent molecular weight of added insulin to 8000, whereas in vivo an additional component of approximately 3000 mol wt is involved to produce the endogenous insulin complex.
妊娠后期（第20天）的胎鼠出现的明显高胰岛素血症被证明是由于胎鼠特有的一种免疫反应性胰岛素（IRI），而非单体胰岛素所致。这种物质在出生后12小时内消失，之后只能检测到成体中存在的胰岛素。胎鼠血清IRI的分子量约为11,000，在凝胶过滤和阴离子交换色谱上的行为与单体胰岛素和胰岛素原不同。基于葡萄糖掺入脂质的胰岛素生物测定中，胎鼠血清的活性仅为根据血清IRI浓度预期活性的一半。向纯化的胰岛素或胰岛素原中加入胎鼠血清会使两种激素的表观分子量增加2000。就胰岛素而言，在葡聚糖凝胶G50上，生成的分子量为8000的物质与内源性物质（11,000）明显不同。发现这个年龄段的胎鼠胰腺主要含有在胰岛素生物测定中具有完全生物活性的单体胰岛素。据推测，胎鼠胰腺分泌单体胰岛素，然后在循环中被修饰为生物活性降低的复合物。这个过程似乎有两个步骤，因为体外胎鼠血清会使添加的胰岛素表观分子量增加到8000，而在体内，大约分子量为3000的另一种成分参与形成内源性胰岛素复合物。
