Phillips I D, Arany E, Strain A J, Han V K, Hill D J
Department of Medicine, University of Western Ontario, London, Canada.
J Endocrinol. 1993 May;137(2):271-80. doi: 10.1677/joe.0.1370271.
The presence of insulin-like growth factors (IGFs) in blood is regulated by their association with specific IGF-binding proteins (IGFBPs). In turn, the level of IGFBPs in the blood is likely to depend on a dynamic equilibrium between peptide production and clearance to extravascular tissues or organ-specific degradation. Since circulating IGFBPs may largely derive from liver we have employed partial hepatectomy in the rat to study the clearance rate of endogenous IGFBPs from blood once a major site of production is removed. Adult male rats were partially hepatectomized and serum and the remaining liver removed between 30 min and 7 days after surgery. Ligand blot analysis revealed two major species of IGFBP, of 28-30 kDa and 40-44 kDa in sera from control rats or sham-operated rats respectively. The larger species corresponded in size to rat IGFBP-3, but the smaller form was not recognized by antisera against rat IGFBP-1, bovine IGFBP-2 or human IGFBP-5 following Western immunoblot. Following hepatectomy, the levels of both IGFBP forms in the serum declined within 30 min and were barely detectable after 3 h or 6 h. They began to increase again in serum 24 h following surgery. The reduction in IGFBPs following hepatectomy was not primarily due to degradation by specific proteases in serum. Circulating levels of insulin were increased fivefold 3 h after hepatectomy but subsequently returned to control values. The rise in insulin was accompanied by a significant (P < 0.05) reduction in circulating IGF-I after 3 h which persisted at 24 h. Glucose levels in serum showed a transient but non-significant reduction between 90 min and 6 h after hepatectomy. Total RNA was extracted from remnant liver and subjected to Northern blot hybridization with 32P-labelled cDNAs encoding rat IGFBP-1, -2 or -3. Messenger RNA encoding IGFBP-1 was barely detectable in liver from control or sham-operated animals, but increased within 30 min of partial hepatectomy and peaked at 3 h. It subsequently declined and was again barely detectable after 24 h. No expression of IGFBP-2 or -3 mRNAs was found by Northern blot analysis in the liver of control animals or following partial hepatectomy. These results suggest that both IGF-I and IGFBPs in rat serum decreased rapidly following partial hepatectomy, and that this was due largely to the rapid clearance of the peptide and its binding proteins once the major source of production was removed.(ABSTRACT TRUNCATED AT 400 WORDS)
血液中胰岛素样生长因子（IGFs）的存在是由它们与特定的IGF结合蛋白（IGFBPs）的结合来调节的。反过来，血液中IGFBPs的水平可能取决于肽的产生与向血管外组织清除或器官特异性降解之间的动态平衡。由于循环中的IGFBPs可能主要来源于肝脏，我们采用大鼠部分肝切除术来研究一旦主要产生部位被切除后，内源性IGFBPs从血液中的清除率。成年雄性大鼠接受部分肝切除术，并在术后30分钟至7天之间采集血清和剩余肝脏。配体印迹分析显示，对照大鼠或假手术大鼠血清中分别有两种主要的IGFBP，分子量分别为28 - 30 kDa和40 - 44 kDa。较大的一种在大小上与大鼠IGFBP - 3相对应，但较小的形式在Western免疫印迹后未被抗大鼠IGFBP - 1、牛IGFBP - 2或人IGFBP - 5的抗血清识别。肝切除术后，血清中两种IGFBP形式的水平在30分钟内下降，3小时或6小时后几乎检测不到。术后24小时血清中它们又开始再次升高。肝切除术后IGFBPs的减少主要不是由于血清中特定蛋白酶的降解。肝切除术后3小时胰岛素的循环水平增加了五倍，但随后恢复到对照值。胰岛素升高伴随着3小时后循环IGF - I的显著（P < 0.05）降低，这种降低在24小时时仍然存在。肝切除术后90分钟至6小时之间血清葡萄糖水平出现短暂但不显著的降低。从剩余肝脏中提取总RNA，并与编码大鼠IGFBP - 1、 - 2或 - 3的32P标记的cDNA进行Northern印迹杂交。在对照或假手术动物的肝脏中几乎检测不到编码IGFBP - 1的信使RNA，但在部分肝切除术后30分钟内增加，并在3小时达到峰值。随后下降，24小时后再次几乎检测不到。Northern印迹分析在对照动物肝脏或部分肝切除术后未发现IGFBP - 2或 - 3 mRNA的表达。这些结果表明，大鼠部分肝切除术后血清中的IGF - I和IGFBPs均迅速下降，这主要是由于一旦主要产生来源被切除，肽及其结合蛋白的快速清除。（摘要截短至400字）
