Frystyk J, Delhanty P J, Skjaerbaek C, Baxter R C
Kolling Institute of Medical Research, Royal North Shore Hospital, University of Sydney, Sydney, New South Wales 2065, Australia.
Am J Physiol. 1999 Aug;277(2):E245-52. doi: 10.1152/ajpendo.1999.277.2.E245.
There is little information on free insulin-like growth factor I (IGF-I) and its regulatory proteins during fasting and refeeding. Therefore, we examined rats during fasting (0, 1, 2, and 3 days) and refeeding (3, 6, and 12 h and 1, 2, 3, and 7 days) (n = 6-9). Serum was analyzed for insulin, C-peptide, growth hormone (GH), free and total IGF-I, IGF-binding protein (IGFBP)-1 and -3, and the acid-labile subunit (ALS). Additionally, liver mRNA for IGF-I, IGFBP-1, and ALS was determined. Fasting reduced serum levels of GH, free and total IGF-I, IGFBP-3, and ALS, whereas IGFBP-1 was increased (P < 0.0001). Refeeding normalized IGFBP-1 at 3 h and GH at 12 h. Free IGF-I changed in parallel with total IGF-I, ALS, and IGFBP-3, being normalized at 48 h of refeeding. IGFBP-1 (peptide and mRNA) correlated inversely with insulin and C-peptide (P < 0.001). The correlation between peptide and mRNA was relatively strong for IGFBP-1 (r(2) = 0.36; P < 0.0001), moderate for IGF-I (r(2) = 0.18; P < 0.0005), and insignificant for ALS. In conclusion, insulin appears to regulate IGFBP-1 in fasted and refed rats. However, the normal inverse relationship between free IGF-I and IGFBP-1 was absent, and free IGF-I changed in parallel with total IGF-I and thus ALS and IGFBP-3. Finally, the regulation of the hepatic synthesis of IGF-I, IGFBP-1, and ALS seems to differ substantially.
关于空腹和重新喂食期间游离胰岛素样生长因子I（IGF-I）及其调节蛋白的信息很少。因此，我们对大鼠在空腹（0、1、2和3天）和重新喂食（3、6和12小时以及1、2、3和7天）期间进行了研究（n = 6 - 9）。分析血清中的胰岛素、C肽、生长激素（GH）、游离和总IGF-I、IGF结合蛋白（IGFBP）-1和-3以及酸不稳定亚基（ALS）。此外，还测定了肝脏中IGF-I、IGFBP-1和ALS的mRNA。空腹降低了血清中GH、游离和总IGF-I、IGFBP-3和ALS的水平，而IGFBP-1升高（P < 0.0001）。重新喂食在3小时使IGFBP-1恢复正常，在12小时使GH恢复正常。游离IGF-I与总IGF-I、ALS和IGFBP-3平行变化，在重新喂食48小时时恢复正常。IGFBP-1（肽和mRNA）与胰岛素和C肽呈负相关（P < 0.001）。对于IGFBP-1，肽与mRNA之间的相关性相对较强（r(2) = 0.36；P < 0.0001），对于IGF-I为中等（r(2) = 0.18；P < 0.0005），对于ALS则不显著。总之，胰岛素似乎在空腹和重新喂食的大鼠中调节IGFBP-1。然而，游离IGF-I与IGFBP-1之间正常的负相关关系不存在，游离IGF-I与总IGF-I平行变化，因此也与ALS和IGFBP-3平行变化。最后，肝脏中IGF-I、IGFBP-1和ALS合成的调节似乎有很大差异。
