GLUCOCORTICOIDS, HYPOGLYCEMIA & BRAIN GLUCOSE TRANSPORT

低血糖是许多糖尿病患者，尤其是1型糖尿病患者实现良好血糖控制的障碍。无法察觉低血糖，对低血糖没有意识，以及无法建立一个具有保护作用的反胰岛素激素防御——有缺陷的反调节——是糖尿病患者反复发生严重低血糖的最重要的危险因素。最近来自几条不同研究线的证据表明，影响大脑的一种常见激素机制可能是低血糖无意识和有缺陷的反调节的基础。首先，糖皮质激素应激激素可能在诱导低血糖无意识和有缺陷的反调节中起重要作用。第二，营养葡萄糖进入脑细胞的运输也可能是这两种相互关联现象的基础。第三，大脑的某些关键区域，特别是腹内侧下丘脑和海马体，可能参与导致低血糖无意识和缺陷的信号转导。第四，前期工作表明糖皮质激素可以改变脑葡萄糖转运蛋白的表达。因此，提出的研究将验证低血糖诱导糖皮质激素应激激素的假设，通过这样做，这些激素有助于改变大脑关键区域的脑葡萄糖运输和代谢，这是随后有缺陷的抗胰岛素保护激素反应的主要基础。这个项目的具体目标是：1。确定给予大鼠轻度和更显著的皮质酮应激水平如何影响脑GLUT1和GLUT3蛋白和mRNA的区域表达。2. 确定反复低血糖如何影响局部脑GLUT1和GLUT3蛋白和mRNA表达。3. 确定应激水平皮质酮给予大鼠和慢性胰岛素低血糖如何影响低血糖诱导的应激反应。4. 确定胰岛素低血糖后糖皮质激素分泌的药物阻断如何影响脑内GLUT1和GLUT3的表达及低血糖反调节。我们将测试腹内侧下丘脑和海马的形成是否受到慢性低血糖和糖皮质激素过量导致的脑葡萄糖转运蛋白的调节。我们的实验室拥有适合精细免疫细胞化学定位的高亲和力抗体，能够独特地评估脑葡萄糖转运蛋白变化的精确解剖定位。我们将在大鼠中评估慢性低血糖后对单次低血糖的反调节反应。我们将测试糖皮质激素治疗是否会在低血糖后引起类似的缺陷反调节。最后，我们将评估阻断低血糖诱导的糖皮质激素过量是否可以防止大脑中这些关键区域GLUT表达的改变，从而防止急性低血糖时有缺陷的反调节反应。这些研究应该能让我们深入了解低血糖对大脑的影响。它们可能潜在地导致更安全的是实现良好的糖尿病控制。

Hypoglycemia is the barrier to excellent glycemic control for many patients with diabetes, especially those with Type 1 diabetes. The inability to perceive hypoglycemia, hypoglycemia unawareness, and the inability to mount a protective counter- insulin hormonal defense--- defective counterregulation--- are the most important risk factors for repeated and serious hypoglycemia in those with diabetes. Recent evidence from several differing lines of investigation suggest a common hormonal mechanism affecting the brain could underlie much of hypoglycemia unawareness and defective counterregulation. First, glucocorticoid stress hormones may be important in inducing hypoglycemia unawareness and defective counterregulation. Second, transport of nutrient glucose into brain cells may also underlie these two interrelated phenomena. Third, certain key areas of the brain, in particular the ventromedial hypothalamus and hippocampus, may be involved in the defective signal transduction that underlies hypoglycemia unawareness and defective counterregulation. Fourth, preliminary work shows that glucocorticoids modify brain glucose transporter expression. Thus, the studies proposed will test the hypothesis that hypoglycemia induces glucocorticoid stress hormones and that by doing so, these hormones help to alter brain glucose transport and metabolism in key areas of the brain that are a major basis for subsequent, defective counter-insulin protective hormonal responses. This project's specific aims are to: 1. Determine how mild and more marked stress levels of corticosterone administered to rats affect regional expression of brain GLUT1 and GLUT3 protein and mRNA. 2. Determine how repeated hypoglycemia affects regional brain GLUT1 and GLUT3 protein and mRNA expression. 3. Determine how stress levels of corticosterone administered to rats and chronic insulin hypoglycemia affect hypoglycemia-induced stress responses. 4. Determine how pharmacological blockade of glucocorticoid secretion after insulin hypoglycemia affects brain expression of GLUT1 and GLUT3 and hypoglycemia counterregulation. We will test whether the ventromedial hypothalamus and hippocampal formation, in particular, are subject to regulation of brain glucose transport proteins as a result of chronic hypoglycemia and glucocorticoid excess. With high affinity antibodies suitable for fine immunocytochemical localization, our lab is uniquely able to assess precise anatomic localization of brain glucose transporter changes. We will assess in rats the counterregulation response to a single bout of hypoglycemia after prior chronic hypoglycemia. We will test whether glucocorticoid treatment induces similar defective counterregulation after hypoglycemia. Finally, we will assess whether blockade of hypoglycemia induced glucocorticoid excess may prevent altered brain GLUT expression in these key areas and thereby prevent defective counterregulation responses to acute hypoglycemia. These studies should provide insight into hypoglycemia's impact upon the brain. They may potentially lead to safer was to achieve good diabetes control.