Remodeling of rat neonatal pulmonary artery: Role of matrix metalloproteinases

We studied whether rapid thinning of large pulmonary arteries of neonatal r ats is associated with breakdown of collagen. Pulmonary artery extracts fro m fetal to 21 days of age were assayed for collagen content and matrix meta lloproteinases. Within 3 days postpartum, no changes in collagen content, c ollagenolytic activity, or levels of stromelysin -1 or gelatinase A were ob served. After day 3, collagen content and total proteolytic activity increa sed with little change in matrix metalloproteinase expression. Thus, collag en was not degraded, and the late increases in collagen and total proteolyt ic activity were probably growth related. Unlike adult rats in which collag en is broken down after reversal of hypoxic pulmonary artery remodeling, co llagen is not broken down in neonatal pulmonary arteries during adaptation to extrauterine life.