Ornan David A, Chaudry Irshad H, Wang Ping
Center for Surgical Research and Department of Surgery, The University of Alabama at Birmingham, 1670 University Boulevard, Volker Hall, Room G094P, 35294, USA.
Biochim Biophys Acta. 2002 Apr 24;1586(3):299-306. doi: 10.1016/s0925-4439(01)00108-9.
Adrenomedullin (AM) is a potent vasodilator that plays a major role in the cardiovascular response during the progression of sepsis. Although pulmonary clearance of AM (i.e., the primary site of AM clearance) is reduced during the late, hypodynamic stage of sepsis, the role of AM receptors under such conditions remains unclear. This study was carried out to test the hypothesis that saturation of AM receptors is responsible for the decreased clearance of AM in the lungs during sepsis. Polymicrobial sepsis was induced in male adult rats by cecal ligation and puncture (CLP). At 20 h after CLP (i.e., the late phase), 125I-labeled rat AM was administered through the jugular vein, both with (+) and without (-) pre-injection of the human AM fragment AM(22-52) (an AM receptor antagonist). Pulmonary tissue samples were harvested after 30 min and the radioactivity was determined. In addition, lung levels of AM were determined at 5 and 20 h after CLP by radioimmunoassay. Alterations in gene expression of the recently identified AM receptor subunits calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein-2 and -3 (RAMP-2 and -3) were assessed in the lungs by reverse transcription-polymerase chain reaction (RT-PCR) at 5 and 20 h after CLP. The results indicate that there was a significant decrease in pulmonary [125I]AM clearance at 20 h in -AM(22-52) CLP animals. Lung clearance in +AM(22-52) sham animals was significantly lower than in -AM(22-52) sham animals and was not statistically different from the -AM(22-52) CLP group. There was no statistical difference between +AM(22-52) and -AM(22-52) CLP groups. However, there was a significant increase in lung AM levels at 20 but not 5 h after CLP. In addition, RAMP-3 expression was significantly upregulated at 5 but not 20 h after CLP. There were no alterations in the expression of CRLR or RAMP-2 at either time point. These results suggest that pulmonary AM receptors become saturated as more AM enters the bloodstream, thereby reducing the ability of the lungs to clear this peptide during late sepsis. Early upregulation of RAMP-3 may be a compensatory mechanism to help clear the upregulated AM from the bloodstream. The lack of upregulation of RAMP-3 during late sepsis could also contribute to the decreased clearance observed during this phase.
肾上腺髓质素（AM）是一种强效血管舒张剂，在脓毒症进展过程中的心血管反应中起主要作用。尽管在脓毒症晚期的低动力阶段，AM的肺清除率（即AM清除的主要部位）降低，但在这种情况下AM受体的作用仍不清楚。本研究旨在验证脓毒症期间AM受体饱和是肺部AM清除率降低的原因这一假设。通过盲肠结扎和穿刺（CLP）诱导成年雄性大鼠发生多微生物脓毒症。在CLP后20小时（即晚期），通过颈静脉注射125I标记的大鼠AM，同时预先注射（+）和不预先注射（-）人AM片段AM(22 - 52)（一种AM受体拮抗剂）。30分钟后采集肺组织样本并测定放射性。此外，通过放射免疫测定法在CLP后5小时和20小时测定肺中AM的水平。在CLP后5小时和20小时，通过逆转录聚合酶链反应（RT-PCR）评估肺中最近鉴定的AM受体亚基降钙素受体样受体（CRLR）以及受体活性修饰蛋白-2和-3（RAMP-2和-3）的基因表达变化。结果表明，在-AM(22 - 52) CLP动物中，20小时时肺中[125I]AM清除率显著降低。+AM(22 - 52)假手术动物的肺清除率显著低于-AM(22 - 52)假手术动物，且与-AM(22 - 52) CLP组无统计学差异。+AM(22 - 52)和-AM(22 - 52) CLP组之间无统计学差异。然而，CLP后20小时而非5小时肺中AM水平显著升高。此外，CLP后5小时而非20小时RAMP-3表达显著上调。在两个时间点CRLR或RAMP-2的表达均无变化。这些结果表明，随着更多AM进入血液，肺AM受体饱和，从而降低了脓毒症晚期肺清除该肽的能力。RAMP-3的早期上调可能是一种补偿机制，有助于从血液中清除上调的AM。脓毒症晚期RAMP-3缺乏上调也可能导致此阶段观察到的清除率降低。
