Vascular Connective Tissue is Rapidly Degraded During Early Regression of Pulmonary Hypertension

We conclude that proteolytic activity in pulmonary arteries transiently increases during early recovery from hypoxia. Procollagenase-positive material appears to be produced by mast cells that increase in number in late hypoxia and early recovery. We speculate that release of hypoxic vasoconstriction following return to normoxia results in a reduction in intraluminal wall tension in central pulmonary arteries, which may be a physiologic stimulus leading to the increase of proteolytic activity. Our data suggest that reversal of structural changes in central pulmonary arteries caused by chronic hypoxia is the result of local production of enzymes capable of degrading matrix proteins. Mechanical factors such as a reduction in intraluminal pressure may trigger processes leading to the release and/or activation of these proteases.