POSTPNEUMONECTOMY LUNG GROWTH - A MODEL OF REINITIATION OF TROPOELASTIN AND TYPE-I COLLAGEN PRODUCTION IN A NORMAL PATTERN IN ADULT-RAT LUNG

Elastic and collagen fibers confer recoil and tensile strength on the pulmonary vasculature, airways, alveolar walls, and pleura. These dura ble extracellular matrix components are primarily synthesized during l ung development and growth, and are expressed at very low levels in he althy adult lung. However, reinitiation of elastin and collagen synthe sis in diseases of adult lung, such as idiopathic pulmonary fibrosis, often leads to excessive or aberrant deposition of elastin and collage n which contribute to the pathophysiology of these diseases. We used a n experimental model of postpneumonectomy lung growth to determine whe ther normal patterns of synthesis and deposition of these critical str uctural components can occur in the adult lung. Male Sprague-Dawley ra ts (250-300 grams) were subjected to left pneumonectomy and right lobe ctomy. The remaining lung tissue was harvested for analysis after 3, 7 , or 14 days, Compensatory growth of the remaining right lung progress ed throughout the time course. Total desmosine and hydroxyproline cont ent increased in the postpneumonectomy lung, reflecting increased elas tin and collagen accumulation, but both were normal in content per wei ght of lung tissue. Northern analysis demonstrated induction of tropoe lastin and type I procollagen mRNA expression in lungs of pneumonectom y rats. In situ hybridization localized tropoelastin and type I procol lagen mRNA expression to anatomical sites similar to those seen during lung development. These data indicate that the adult lung can reiniti ate elastin and collagen production and deposit these extracellular ma trix components in a normal pattern.