Harrison H C, Goodner C J, Berrie M A
Department of Medicine, University of Washington, Seattle.
Diabetes. 1991 Aug;40(8):990-7. doi: 10.2337/diab.40.8.990.
Hepatic glucose production is stimulated in vitro twice as effectively by pulsatile as by continuous glucagon, given equivalent time-averaged doses. Efficacy studies of pulsatile insulin have yielded conflicting results. In the rat hepatoma cell line H-4-II-E-C3, insulin rapidly (t1/2 15 min) inhibits transcription of the gene and lowers mRNA levels for the gluconeogenic enzyme. PEPCK via a receptor-mediated process. We attached H-4-II-E-C3 cells to Cytodex-3 microcarriers and used a perifusion column system to test whether pulsatile insulin is more or less effective than equivalent time-averaged doses of continuous insulin. PEPCK transcription was induced by inclusion of cAMP analogue 8-(4-chlorophenyl-thio)-cAMP (0.1 mM) and dexamethasone (0.5 microM) in the perifusion medium. Three columns were exposed either to continuous, pulsatile, or no insulin. After 3 h, total nucleic acid was extracted, and mRNA(PEPCK) was measured with a sensitive-solution hybridization assay. Continuous insulin inhibited PEPCK expression in a dose-dependent fashion with EC50 1 x 10(-11) M. Equivalent time-averaged amounts of insulin delivered as pulses achieved significant inhibition but less effectively than continuous insulin. The apparent EC50 for pulsatile insulin increased from 2 x 10(-11) M to 5 x 10(-11) M as the oscillatory period was raised from 5 to 20 min, respectively. These observations suggest that insulin-mediated inhibition of PEPCK gene transcription is diminished by a pulsatile mode of administration in marked contrast to the pulse enhancement demonstrated for glucagon-mediated hepatic glucose production.
在给予等效时间平均剂量的情况下，体外实验中，脉冲式胰高血糖素刺激肝葡萄糖生成的效果是持续性胰高血糖素的两倍。脉冲式胰岛素的功效研究结果相互矛盾。在大鼠肝癌细胞系H-4-II-E-C3中，胰岛素迅速（半衰期15分钟）抑制该基因的转录，并通过受体介导的过程降低糖异生酶磷酸烯醇式丙酮酸羧激酶（PEPCK）的mRNA水平。我们将H-4-II-E-C3细胞附着于Cytodex-3微载体上，并使用灌注柱系统来测试脉冲式胰岛素与等效时间平均剂量的持续性胰岛素相比，其效果是更好还是更差。通过在灌注培养基中加入环磷酸腺苷类似物8-（4-氯苯基硫代）-环磷酸腺苷（0.1 mM）和地塞米松（0.5 microM）来诱导PEPCK转录。三个灌注柱分别暴露于持续性胰岛素、脉冲式胰岛素或无胰岛素环境中。3小时后，提取总核酸，并用灵敏溶液杂交分析法测量mRNA（PEPCK）。持续性胰岛素以剂量依赖性方式抑制PEPCK表达，半数有效浓度（EC50）为1×10⁻¹¹ M。以脉冲形式给予的等效时间平均量的胰岛素可实现显著抑制，但效果不如持续性胰岛素。随着振荡周期从5分钟增加到20分钟，脉冲式胰岛素的表观EC50分别从2×10⁻¹¹ M增加到5×10⁻¹¹ M。这些观察结果表明，与胰高血糖素介导的肝葡萄糖生成的脉冲增强作用形成鲜明对比的是，脉冲式给药方式会减弱胰岛素介导的对PEPCK基因转录的抑制作用。
