RETINOIC ACID EFFECT ON POSTPNEUMONECTOMY LUNG GROWTH

我们以前的研究表明，通过生理和形态测量的方法，新的肺泡和腺泡气道生长发生在肺切除术（PNX）后，在成年狗的剩余肺。左侧PNX（45%切除）后未发生再生性肺生长;生理补偿是通过招募现有毛细血管储备实现的，右侧PNX（55%切除）后发生功能显著性生长，但不完全，因此运动能力、气体交换和机械功能异常持续存在。当右PNX后通过可膨胀假体防止纵隔移位时，仍然发生再生肺生长，证明肺拉伸不是唯一的生长信号。在诱导肺气肿后的大鼠中，视黄酸也可以在没有施加拉伸的情况下增加肺生长;然而，大鼠的躯体生长在整个生命中持续存在。对视黄酸的结构反应与功能无关，也没有在成年后停止生长的大型成熟动物中测量。我们将使用我们的成年狗模型探索维甲酸对PNX后肺生长的体内作用和作用机制。假设：1）45%肺切除后，肺生长未能发生，维甲酸将诱导肺泡和腺泡气道生长。2)在发生不完全再生生长的55%肺切除后，视黄酸将显著增加生长。3)生长诱导的视黄酸将改善气体交换和机械功能。4)视黄酸的一种作用机制是在PNX后诱导表皮生长因子（EGF）和/或其受体（EGFR）和/或其受体（EGFR），增强肺生长。在左侧PNX、右侧PNX或SHAM手术后（6个实验组），将给予全反式维甲酸或其稀释剂，每周5天，持续3个月。每隔一段时间，将测量肺力学、肺弥散量、膜弥散量、毛细血管血容量和肺组织体积，并获得高分辨率CT扫描以评估体内肺组织体积和气道尺寸。在3个月或6个月时收获肺，用于肺泡隔的结构变化、腺泡气道的尺寸和数量、肺泡和毛细血管表面积以及形态测定扩散能力的形态测定定量。EGF和EGFR的解剖分布和体内表达将通过免疫组织化学、免疫金标记、免疫印迹和RNA印迹来确定。结果将定义维甲酸对大型完全发育的哺乳动物的成熟肺中再生生长的结构和生理作用，并确定维甲酸对EGF和EGFR的体内作用。

Our previous studies have shown by physiologic and morphometric methods that new alveolar and acinar airway growth occurs in the remaining lung after pneumonectomy (PNX) in adult dogs. Regenerative lung growth did not occur after left PNX (45% resection); physiologic compensation was by recruitment of existing capillary reserves functionally significant growth occurred after right PNX (55% resection) but was incomplete, so that abnormalities in exercise capacity, gas exchange and mechanical function persisted. Regenerative lung growth still occurred when mediastinal shift was prevented by an inflatable prosthesis after right PNX, proving that lung stretch was not the only growth signal. In rats after induction of emphysema, retinoic acid can also augment lung growth in the absence of applied stretch; however, somatic growth persists in rats throughout life. The structural response to retinoic acid has not been correlated with function, nor measured in large mature animals that stop growing as adults. We will explore in vivo effects and mechanisms of action of retinoic acid on post-PNX lung growth using our adult dog model. Hypotheses are: 1) After 45% lung resection where lung growth failed to occur, retinoic acid will induce alveolar and acinar airway growth. 2) After 55% lung resection where incomplete regenerative growth occurred, retinoic acid will significantly augment growth. 3) Growth induced retinoic acid will improve gas exchange and mechanical function. 4) One mechanism of action by retinoic acid will be induction of epidermal growth factor (EGF) and/or its receptor (EGFR) and/or its receptor (EGFR) after PNX, enhancing lung growth. All-trans retinoic acid or its diluent will be administered 5 days/week for 3 months after left PNX, right PNX or SHAM surgery (6 experimental groups). At intervals,. Lung mechanics, lung diffusing capacity, membrane diffusing capacity, capillary blood volume and lung tissue volume will be measured and high resolution CT scan obtained to asess in vivo lung tissue volume and airway dimensions. Lungs are harvested at 3 or 6 months for morphometric quantification of structural changes in alveolar septa, dimensions and number of acinar airways, alveolar and capillary surface areas, and morphometric diffusing capacity. Anatomic distribution and in vivo expression of EGF and EGFR will be determined by immunohistochemistry, immunogold labeling, immunoblots and RNA blots. Results will define both structural and physiological effects of retinoic acid on regenerative growth in the mature lung of a large fully grown mammal, and determine the in vivo effect of retinoic acid on EGF and EGFR.