Role of Pulsatile Insulin Secretion

描述（由申请人提供）：1型和2型糖尿病的患病率都在增加。两者的特点都是分泌胰岛素的胰腺细胞减少。1型和2型糖尿病都以胰岛素抵抗为特征。虽然这可以通过注射更多的胰岛素来克服，但糖尿病患者的胰岛素抵抗会增加患心脏病、中风和截肢的风险。在拟议的研究中，我们将检验一个假设，即糖尿病患者产生胰岛素抵抗的原因之一是当β细胞数量减少到正常水平的50%以下时，胰岛素分泌模式受到干扰。在健康中，几乎所有的胰岛素都是在离散的胰岛素分泌爆发中分泌的。糖尿病患者分泌的胰岛素不足是因为分泌量太小。一旦β细胞的数量下降到正常水平的50%以下，我们假定胰岛素脉冲的大小会减小，因为剩余的β细胞无法产生足够的胰岛素来维持这些分泌爆发。然而，我们认为这并不明显，因为至少在最初，肝脏对胰岛素的胰岛素清除率随着胰岛素分泌的减少而减少，因此循环胰岛素的量保持相对正常。那么为什么这一切都很重要呢？人们早就认识到，当人们接近发展为糖尿病（空腹葡萄糖受损/葡萄糖耐受不良）时，这种状态相对不稳定，并迅速发展为糖尿病。我们认为，支持这一现象的原因是IFG/IGT暗示在许多情况下，β细胞质量下降到正常搏动胰岛素分泌的50%左右，因此胰岛素抵抗增加。我们认为，胰岛素需求的增加和维持胰岛素分泌能力的下降共同影响导致失代偿和糖尿病的发病。如果我们是正确的，那么针对β细胞质量下降的机制将是预防1型和2型糖尿病最基本的方法。在拟议的研究中，我们将首先检查50%胰腺切除术和IFG/IGT患者与对照组的搏动胰岛素分泌和胰岛素敏感性。其次，我们将直接建立脉冲胰岛素分泌在体内的生理作用，最后我们将研究脉冲胰岛素分泌增强靶组织胰岛素信号传导的机制。公共卫生相关性：2型糖尿病是美国过早死亡的主要原因，涉及超过2000万人。目前的拨款建议继续资助旨在为从空腹血糖受损到糖尿病的患者过渡建立基础的研究。如果知道这种转变的基础，那么建立预防2型糖尿病的策略将更加现实。

DESCRIPTION (provided by applicant): Both type 1 and type 2 diabetes are increasing in prevalence. Both are characterized by a loss of insulin secreting pancreatic beta cells. Type1 and Type 2 diabetes are both characterized by insulin resistance. Although this can be overcome by administering more insulin, insulin resistance in diabetes confers increased risk for heart disease, strokes and amputation. In the proposed studies, we will test the hypothesis that one of the reasons people with diabetes develops insulin resistance is because the pattern of insulin secretion is disturbed when the number of beta cells decreases below ~50% of normal. In health, almost all insulin is secreted in discrete insulin secretory bursts. In people with diabetes insufficient insulin is secreted because the size of the secretory bursts is too small. Once the number of beta cells drops below ~50% of normal, we postulate the size of the insulin pulses decreases as the remaining beta cells are unable to generate sufficient insulin to sustain these secretory bursts. However, we propose that this is not obvious because, at least initially, hepatic insulin clearance of insulin decreases as insulin secretion declines, so that the amount of circulating insulin remains relatively normal. So why does all this matter? It has long been appreciated that as people get close to developing diabetes (Impaired fasting glucose/glucose intolerance) this state is relatively unstable with rapid progression to diabetes. We propose that the reason underpinning this is that IFG/IGT imply in many cases that the beta cell mass has declined to ~50% of normal, pulsatile insulin secretion declines and as a consequence insulin resistance is increased. We suggest that the collective impact of this increment in insulin demand and decreased capacity to sustain insulin secretion leads to decompensation and onset of diabetes. If we are correct, then targeting the mechanisms subserving the decline in beta cell mass will be the most rationale approach to preventing type 1 and 2 diabetes. In the proposed studies, we will first examine humans with an ~50% pancreatectomy and those with IFG/IGT compared to controls for pulsatile insulin secretion and insulin sensitivity. Second we will directly establish the physiological role of pulsatile insulin secretion in vivo and finally we will examine the mechanism by which pulsatile insulin secretion enhances insulin signaling in target tissues. PUBLIC HEALTH RELEVANCE: Type 2 diabetes is a leading cause of premature death in the USA involving more than 20 million people. The present grant proposes continued funding of studied designed to establish the basis for the transition of patients from impaired fasting glucose to diabetes. If the basis of this transition was known it would be more realistic to establish strategies to prevent type 2 diabetes.