Regulation of Renal Cortical Adenosine Levels

描述（由申请人提供）：由于肾皮质表达高亲和力的1型腺苷受体，可调节肾小球前微血管张力、肾素释放和钠重吸收，因此了解肾皮质间质腺苷水平是如何被调节的非常重要。由于我们对肾皮质间质腺苷调节的理解是初步的，本建议的总体目的是进一步我们在这方面的知识。胰腺的静脉引流直接进入门静脉循环，这种解剖结构使胰腺激素在肝细胞上的浓度最大化，从而发挥最大的作用。胰高血糖素是一种分泌到门静脉循环中的胰腺激素。重要的是，胰高血糖素是肝腺苷酸环化酶的强效兴奋剂，肝腺苷酸环化酶的激活会导致大量环AMP释放到体循环中。我们假设全身环AMP（由肝脏对胰高血糖素的反应分泌）通过致密的小管周围毛细血管网络传递到肾皮质，并通过外磷酸二酯酶（将环AMP转化为AMP）和外磷酸5′-核苷酸酶（将AMP转化为腺苷）的连续作用在肾皮质代谢为腺苷。根据这种观点，肝脏分泌一种内分泌促激素（环AMP），在靶组织（肾皮质间质间隙）中，通过一组特定的酶（外磷酸二酯酶和外磷酸5′-核苷酸酶）被局部代谢为一种具有生物活性的激素（腺苷）。本提案的具体目标是使用我们新开发的独特的LC/MS离子捕获法检测嘌呤来验证这一创新假设。所提出的机制将在体外和体内进行研究。在体外，我们将确定添加到近曲小管基底外侧的环AMP是否会被提议的酶迅速代谢为腺苷。在体内，我们将确定适当的操作是否通过涉及所提出的酶的机制适当地影响肾皮质间质室中环AMP和腺苷的水平。这项工作可能确定胰腺和肝脏调节肾皮质间质腺苷水平的新途径，并可能揭示诸如肝肾综合征和代谢综合征X等疾病的重要机制见解。

DESCRIPTION (provided by applicant): Because the renal cortex expresses high affinity type 1 adenosine receptors that modulate preglomerular microvascular tone, renin release and sodium reabsorption, it is important to understand how renal cortical interstitial levels of adenosine are regulated. Because our comprehension of the regulation of renal cortical interstitial adenosine is rudimentary, the overall purpose of this proposal is to further our knowledge in this regard. The venous drainage of the pancreas empties directly into the portal circulation, an anatomical arrangement that maximizes concentrations, and therefore effects, of pancreatic hormones on hepatocytes. Glucagon is a pancreatic hormone secreted into the portal circulation. Importantly, glucagon is a powerful stimulant of hepatic adenylyl cyclase, and activation of hepatic adenylyl cyclase causes release of large quantities of cyclic AMP into the systemic circulation. We hypothesize that systemic cyclic AMP (secreted from the liver in response to glucagon) is delivered to the renal cortex via the dense peritubular capillary network and is metabolized in the renal cortex to adenosine via the sequential actions of ectophosphodiesterase (converts cyclic AMP to AMP) and ecto-5'-nucleotidase (converts AMP to adenosine). In this view, the liver secretes an endocrine pro-hormone (cyclic AMP) that is metabolized locally in the target tissue (renal cortical interstitial space) to a biologically active hormone (adenosine) via a specific set of enzymes (ecto-phosphodiesterase and ecto-5'-nucleotidase). The specific goal of this proposal is to test this innovative hypothesis using our newly developed and unique LC/MS ion trapping assay for purines. The proposed mechanism will be addressed both in vitro and in vivo. In vitro we will determine whether cyclic AMP added to the basolateral aspect of proximal convoluted tubules is rapidly metabolized to adenosine by the proposed enzymes. In vivo we will determine whether the appropriate maneuvers appropriately influence the levels of cyclic AMP and adenosine in the renal cortical interstitial compartment by a mechanism involving the proposed enzymes. This work may identify a novel pathway by which the pancreas and liver regulate renal cortical interstitial levels of adenosine and may reveal important mechanistic insights into diseases such as the hepatorenal syndrome and the metabolic syndrome X.