Morning Meal-Associated Priming of the Liver

在人体器官中，肝脏在餐后条件下提取葡萄糖并将其作为糖原储存，以及在空腹或低血糖状态下保持大量葡萄糖生成的能力几乎是独一无二的。我们之前的工作已经清楚地表明，上午的高胰岛素血症会在下午的高胰岛素血症高血糖钳夹期间增强肝脏葡萄糖摄取和糖原储存，模拟第二餐。我们目前的目标是确定影响饮食反应的因素，这些因素可以用于改善胰岛素抵抗和2型糖尿病患者的护理。具体来说，在目的1中，我们将确定上午高胰岛素血症的哪个方面（对肝脏的直接影响或胰岛素对大脑和/或脂肪组织的间接影响）是参与下午肝糖摄取增强的关键因素。此外，在Aim 2中，我们将确定上午胰岛素输送途径（门静脉内与外周循环）对下午反应的重要性。这个问题与胰岛素依赖型糖尿病患者的治疗高度相关，因为目前大多数可用的胰岛素治疗都是通过外周途径给药。此外，我们将确定下午反应中哪些因素或哪些因素最明显地受到上午高胰岛素血症的影响（目的3）。我们将利用有意识的、长期插管的狗模型，它几乎是独一无二的，因为它不仅可以将葡萄糖和胰岛素输送到门静脉循环中，这是摄入营养物质和分泌胰岛素的通常途径，而且还可以从肝脏和门静脉中取样，以便评估肝脏对治疗的反应。重要的是，犬类模型显示出许多与人类非常相似的生理反应。提出的实验的创新之处包括这样一个事实，即该模型允许我们清楚地分离可能影响对一天中最初和随后的饭菜的反应的因素，并单独检查每个因素的影响。提出的研究非常重要，因为通过这些实验获得的知识有很大的潜力有助于开发新的治疗方法，更准确地为糖耐量受损（前驱糖尿病）和糖尿病患者带来正常的营养配置。

The liver is near-unique among the body organs in its ability to extract glucose and store it as glycogen under postprandial conditions, as well as to maintain a substantial rate of glucose production under fasting or hypoglycemic conditions. Our previous work has clearly shown that a morning period of hyperinsulinemia enhances hepatic glucose uptake and glycogen storage during an afternoon hyperinsulinemic hyperglycemic clamp mimicking a second meal. The goal of our current proposal is to identify factors influencing meal responses that can be utilized in improving the care of those with insulin resistance and type 2 diabetes. Specifically, in Aim 1 we will determine which aspect of morning hyperinsulinemia (direct effects on the liver or indirect effects brought about by insulin’s impact on the brain and/or fat tissues) is the key element involved in enhancement of afternoon hepatic glucose uptake. Furthermore, in Aim 2 we will determine the importance of the route of insulin delivery (intraportal vs peripheral circulation) in the morning on the afternoon response. This question is highly relevant to the treatment of those with insulin-dependent diabetes since most of the currently available insulin therapy involves delivery by a peripheral route. In addition, we will determine what factor or factors in the afternoon response are most clearly impacted by morning hyperinsulinemia (Aim 3). We will utilize the conscious, chronically catheterized dog model which is near-unique in that it not only makes possible the delivery of glucose and insulin into the portal circulation, the usual route of entry for ingested nutrients and secreted insulin, but also permits sampling from the hepatic and portal veins to allow the assessment of the liver’s response to the treatments. Importantly, the canine model has been shown to display many physiologic responses very similar to those in the human. The innovative aspects of the proposed experiments include the fact that the model allows us to clearly separate factors that may impact the response to the initial and subsequent meals of the day and examine the effect of each factor individually. The proposed studies are highly significant because the knowledge gained through these experiments has great potential to contribute to the development of new therapeutic approaches, more accurately tailored to bring about normal nutrient disposition, for those with impaired glucose tolerance (prediabetes) and diabetes.