Denver R J, Nicoll C S
Department of Integrative Biology, University of California, Berkeley 94720.
J Endocrinol. 1994 Aug;142(2):299-310. doi: 10.1677/joe.0.1420299.
We investigated the influence of and interactions among pancreatic hormones on the secretion of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IG-FBPs) by treating primary hepatocytes from young male Long-Evans rats with insulin or glucagon in combination with rat GH (rGH). The concentration of IGF-I secreted into the medium was estimated by radioimmunoassay after formic acid-acetone cryoextraction, and secreted IGFBPs were analysed by Western ligand blot and immunoblot; accumulation of IGF-I mRNA was analysed by Northern blot. Both insulin (0.1-100 nmol/l) and rGH (0.5, 5 and 50 pmol/l) produced a dose-dependent stimulation of IGF-I secretion over a 24-h incubation period. In contrast, glucagon (0.1-100 nmol/l) inhibited IGF-I production in a dose-related manner. Glucagon (10 nmol/l) also inhibited IGF-I secretion stimulated by rGH (5 pmol/l) and insulin (10 nmol/l). Northern blot analysis of total RNA isolated from rat hepatocytes revealed that rGH (5 pmol/l) elevated IGF-I mRNA levels, glucagon (10 nmol/l) alone had no effect on this parameter, but glucagon significantly reduced IGF-I transcript accumulation in response to rGH. IGFBPs secreted by rat hepatocytes run in two molecular weight ranges on SDS-PAGE: approximately 25 kDa (IGFBP-4) and approximately 29-31 kDa (IGFBP-1 and -2); the predominant hormonally regulated IGFBP was identified as IGFBP-1. Insulin produced a dose-dependent inhibition of production of IGFBP-1, while glucagon was stimulatory; when given together at an equivalent concentration (1 nmol/l), the effects of insulin were dominant to glucagon on IGFBP-1. These observations provide support for significant opposite roles for the pancreatic hormones, insulin and glucagon, in the regulation of liver IGF-I and IGFBP-1 production. As the production of pancreatic hormones is influenced by nutritional status, these polypeptides may mediate the effects of changing nutritional state on the hormonal control of protein anabolism and glucose homeostasis by directly influencing the circulating level of liver-derived IGF-I and its binding proteins.
我们通过用胰岛素或胰高血糖素联合大鼠生长激素（rGH）处理年轻雄性Long-Evans大鼠的原代肝细胞，研究了胰腺激素对胰岛素样生长因子-I（IGF-I）和IGF结合蛋白（IG-FBP）分泌的影响及其相互作用。经甲酸 - 丙酮冷冻提取后，通过放射免疫测定法估计分泌到培养基中的IGF-I浓度，通过Western配体印迹和免疫印迹分析分泌的IGFBPs；通过Northern印迹分析IGF-I mRNA的积累。在24小时的孵育期内，胰岛素（0.1 - 100 nmol/l）和rGH（0.5、5和50 pmol/l）均对IGF-I分泌产生剂量依赖性刺激。相反，胰高血糖素（0.1 - 100 nmol/l）以剂量相关的方式抑制IGF-I的产生。胰高血糖素（10 nmol/l）也抑制由rGH（5 pmol/l）和胰岛素（10 nmol/l）刺激的IGF-I分泌。对从大鼠肝细胞分离的总RNA进行Northern印迹分析表明，rGH（5 pmol/l）提高了IGF-I mRNA水平，单独的胰高血糖素（10 nmol/l）对该参数无影响，但胰高血糖素显著降低了rGH刺激下的IGF-I转录本积累。大鼠肝细胞分泌的IGFBPs在SDS-PAGE上呈现两个分子量范围：约25 kDa（IGFBP-4）和约29 - 31 kDa（IGFBP-1和-2）；主要受激素调节的IGFBP被鉴定为IGFBP-1。胰岛素对IGFBP-1的产生产生剂量依赖性抑制，而胰高血糖素具有刺激作用；当以等效浓度（1 nmol/l）一起给予时，胰岛素对IGFBP-1的作用比胰高血糖素占主导。这些观察结果支持胰腺激素胰岛素和胰高血糖素在调节肝脏IGF-I和IGFBP-1产生中具有显著相反的作用。由于胰腺激素的产生受营养状态影响，这些多肽可能通过直接影响肝脏来源的IGF-I及其结合蛋白的循环水平，介导营养状态变化对蛋白质合成代谢和葡萄糖稳态激素控制的影响。
