Dehoff M H, Elgin R G, Collier R J, Clemmons D R
Department of Dairy Science, University of Florida, Gainesville 32611.
Endocrinology. 1988 Jun;122(6):2412-7. doi: 10.1210/endo-122-6-2412.
Bovine GH is a potent stimulant of lactation, and the insulin-like growth factors I and II (IGF-I and -II) are believed to mediate GH's growth-promoting actions. Since all of IGF's known actions are mediated through its receptor subtypes, we analyzed the distribution of IGF receptor subtypes in lactating and nonlactating bovine mammary tissue. Analysis of competition curves showed that IGF-I had greater potency than IGF-II in competing with [125I]IGF-I for binding to membranes prepared from both lactating and nonlactating animals. An insulin concentration of 4 micrograms/ml displaced less than 40% of the [125I]IGF-I bound to membranes prepared from both lactating and nonlactating animals, indicating that a high percentage of [125I]IGF-I was bound to the type II receptor. Lactation was associated with an increase in the total amount of [125I]IGF-I bound, and this change was due to an increase in binding to both receptor subtypes. Specifically, membranes prepared from lactating animals had a 3-fold increase in binding competed for by insulin and a 2-fold increase in binding not competed for by insulin. Affinity cross-linking of [125I]IGF-I to membranes prepared from both lactating and nonlactating animals, followed by polyacrylamide gel electrophoresis (PAGE) and autoradiography, showed that 260K and 135K bands were present. Competition experiments indicated that unlabeled IGF-I effectively competed for binding to the 260K band, whereas insulin did not. Binding to the 135K band could be inhibited by both IGF-I and insulin. The intensity of the labeled bands showed that type II receptors were relatively more abundant than type I receptors in membranes from both lactating and nonlactating animals. Membranes prepared from lactating animals showed both 135K and 127K species of the type I receptor, whereas nonlactating animals showed only the 135K band. We conclude that type I and II receptors are present in bovine mammary tissue, and type II predominate. Lactation is associated with increases in the concentration of both receptor subtypes, especially type I receptors. Lactation may be associated with structural changes in the type I receptor. These changes in receptor distribution could play a role in modulating the physiological effects of the IGFs on mammary tissue.
牛生长激素是一种强效的泌乳刺激剂，胰岛素样生长因子I和II（IGF-I和IGF-II）被认为介导生长激素的促生长作用。由于IGF的所有已知作用都是通过其受体亚型介导的，我们分析了IGF受体亚型在泌乳和非泌乳牛乳腺组织中的分布。竞争曲线分析表明，在与[125I]IGF-I竞争结合泌乳和非泌乳动物制备的膜时，IGF-I比IGF-II具有更高的效力。4微克/毫升的胰岛素浓度使结合到泌乳和非泌乳动物制备的膜上的[125I]IGF-I的取代率不到40%，这表明高比例的[125I]IGF-I与II型受体结合。泌乳与结合的[125I]IGF-I总量增加有关，这种变化是由于与两种受体亚型的结合增加所致。具体而言，泌乳动物制备的膜上，胰岛素竞争结合增加了3倍，非胰岛素竞争结合增加了2倍。将[125I]IGF-I与泌乳和非泌乳动物制备的膜进行亲和交联，然后进行聚丙烯酰胺凝胶电泳（PAGE）和放射自显影，结果显示存在260K和135K条带。竞争实验表明，未标记的IGF-I能有效竞争结合260K条带，而胰岛素则不能。IGF-I和胰岛素均可抑制与135K条带的结合。标记条带的强度表明，在泌乳和非泌乳动物的膜中，II型受体相对比I型受体更丰富。泌乳动物制备的膜显示I型受体有135K和127K两种类型，而非泌乳动物仅显示135K条带。我们得出结论，I型和II型受体存在于牛乳腺组织中，且II型受体占主导。泌乳与两种受体亚型的浓度增加有关，尤其是I型受体。泌乳可能与I型受体的结构变化有关。受体分布的这些变化可能在调节IGF对乳腺组织的生理作用中发挥作用。
